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What's New in Python 3.11.2 final?
==================================

*Release date: 2023-02-07*

Core and Builtins
-----------------

- gh-issue-92173: Fix the ``defs`` and ``kwdefs`` arguments to
:c:func:`PyEval_EvalCodeEx` and a reference leak in that function.

- gh-issue-101400: Fix wrong lineno in exception message on
:keyword:`continue` or :keyword:`break` which are not in a loop. Patch by
Dong-hee Na.

- gh-issue-101372: Fix :func:`~unicodedata.is_normalized` to properly handle
the UCD 3.2.0 cases. Patch by Dong-hee Na.

- gh-issue-101046: Fix a possible memory leak in the parser when raising
:exc:`MemoryError`. Patch by Pablo Galindo

- gh-issue-101037: Fix potential memory underallocation issue for instances
of :class:`int` subclasses with value zero.

- gh-issue-100942: Fixed segfault in property.getter/setter/deleter that
occurred when a property subclass overrode the ``__new__`` method to
return a non-property instance.

- gh-issue-100892: Fix race while iterating over thread states in clearing
:class:`threading.local`. Patch by Kumar Aditya.

- gh-issue-100776: Fix misleading default value in :func:`input`'s
``__text_signature__``.

- gh-issue-100637: Fix :func:`int.__sizeof__` calculation to include the 1
element ob_digit array for 0 and False.

- gh-issue-100649: Update the native_thread_id field of PyThreadState after
fork.

- gh-issue-100374: Fix incorrect result and delay in :func:`socket.getfqdn`.
Patch by Dominic Socular.

- gh-issue-99110: Initialize frame->previous in frameobject.c to fix a
segmentation fault when accessing frames created by :c:func:`PyFrame_New`.

- gh-issue-100050: Honor existing errors obtained when searching for
mismatching parentheses in the tokenizer. Patch by Pablo Galindo

- bpo-32782: ``ctypes`` arrays of length 0 now report a correct itemsize
when a ``memoryview`` is constructed from them, rather than always giving
a value of 0.

Library
-------

- gh-issue-101541: [Enum] - fix psuedo-flag creation

- gh-issue-101326: Fix regression when passing ``None`` as second or third
argument to ``FutureIter.throw``.

- gh-issue-100795: Avoid potential unexpected ``freeaddrinfo`` call (double
free) in :mod:`socket` when when a libc ``getaddrinfo()`` implementation
leaves garbage in an output pointer when returning an error. Original
patch by Sergey G. Brester.

- gh-issue-101143: Remove unused references to :class:`~asyncio.TimerHandle`
in ``asyncio.base_events.BaseEventLoop._add_callback``.

- gh-issue-101144: Make :func:`zipfile.Path.open` and
:func:`zipfile.Path.read_text` also accept ``encoding`` as a positional
argument. This was the behavior in Python 3.9 and earlier. 3.10
introduced a regression where supplying it as a positional argument would
lead to a :exc:`TypeError`.

- gh-issue-101015: Fix :func:`typing.get_type_hints` on ``'*tuple[...]'``
and ``*tuple[...]``. It must not drop the ``Unpack`` part.

- gh-issue-100573: Fix a Windows :mod:`asyncio` bug with named pipes where a
client doing ``os.stat()`` on the pipe would cause an error in the server
that disabled serving future requests.

- gh-issue-100805: Modify :func:`random.choice` implementation to once again
work with NumPy arrays.

- gh-issue-90104: Avoid RecursionError on ``repr`` if a dataclass field
definition has a cyclic reference.

- gh-issue-100750: pass encoding kwarg to subprocess in platform

- gh-issue-100689: Fix crash in :mod:`pyexpat` by statically allocating
``PyExpat_CAPI`` capsule.

- gh-issue-100740: Fix ``unittest.mock.Mock`` not respecting the spec for
attribute names prefixed with ``assert``.

- gh-issue-86508: Fix :func:`asyncio.open_connection` to skip binding to
local addresses of different family. Patch by Kumar Aditya.

- gh-issue-100287: Fix the interaction of :func:`unittest.mock.seal` with
:class:`unittest.mock.AsyncMock`.

- gh-issue-100474: :mod:`http.server` now checks that an index page is
actually a regular file before trying to serve it. This avoids issues
with directories named ``index.html``.

- gh-issue-100160: Remove any deprecation warnings in
:func:`asyncio.get_event_loop`. They are deferred to Python 3.12.

- gh-issue-96290: Fix handling of partial and invalid UNC drives in
``ntpath.splitdrive()``, and in ``ntpath.normpath()`` on non-Windows
systems. Paths such as '\\server' and '\\' are now considered by
``splitdrive()`` to contain only a drive, and consequently are not
modified by ``normpath()`` on non-Windows systems. The behaviour of
``normpath()`` on Windows systems is unaffected, as native OS APIs are
used. Patch by Eryk Sun, with contributions by Barney Gale.

- gh-issue-78878: Fix crash when creating an instance of
:class:`!_ctypes.CField`.

- gh-issue-99952: Fix a reference undercounting issue in
:class:`ctypes.Structure` with ``from_param()`` results larger than a C
pointer.

- gh-issue-100133: Fix regression in :mod:`asyncio` where a subprocess would
sometimes lose data received from pipe.

- gh-issue-100098: Fix ``tuple`` subclasses being cast to ``tuple`` when
used as enum values.

- gh-issue-98778: Update :exc:`~urllib.error.HTTPError` to be initialized
properly, even if the ``fp`` is ``None``. Patch by Dong-hee Na.

- gh-issue-83035: Fix :func:`inspect.getsource` handling of decorator calls
with nested parentheses.

- gh-issue-99576: Fix ``.save()`` method for ``LWPCookieJar`` and
``MozillaCookieJar``: saved file was not truncated on repeated save.

- gh-issue-99433: Fix :mod:`doctest` failure on
:class:`types.MethodWrapperType` in modules.

- gh-issue-99240: Fix double-free bug in Argument Clinic ``str_converter``
by extracting memory clean up to a new ``post_parsing`` section.

- gh-issue-64490: Fix refcount error when arguments are packed to tuple in
Argument Clinic.

- gh-issue-85267: Several improvements to :func:`inspect.signature`'s
handling of ``__text_signature``. - Fixes a case where
:func:`inspect.signature` dropped parameters - Fixes a case where
:func:`inspect.signature` raised :exc:`tokenize.TokenError` - Allows
:func:`inspect.signature` to understand defaults involving binary
operations of constants - :func:`inspect.signature` is documented as only
raising :exc:`TypeError` or :exc:`ValueError`, but sometimes raised
:exc:`RuntimeError`. These cases now raise :exc:`ValueError` - Removed a
dead code path

- gh-issue-95882: Fix a 3.11 regression in
:func:`~contextlib.asynccontextmanager`, which caused it to propagate
exceptions with incorrect tracebacks and fix a 3.11 regression in
:func:`~contextlib.contextmanager`, which caused it to propagate
exceptions with incorrect tracebacks for :exc:`StopIteration`.

- bpo-44817: Ignore WinError 53 (ERROR_BAD_NETPATH), 65
(ERROR_NETWORK_ACCESS_DENIED) and 161 (ERROR_BAD_PATHNAME) when using
ntpath.realpath().

- bpo-40447: Accept :class:`os.PathLike` (such as :class:`pathlib.Path`) in
the ``stripdir`` arguments of :meth:`compileall.compile_file` and
:meth:`compileall.compile_dir`.

- bpo-36880: Fix a reference counting issue when a :mod:`ctypes` callback
with return type :class:`~ctypes.py_object` returns ``None``, which could
cause crashes.

Documentation
-------------

- gh-issue-100616: Document existing ``attr`` parameter to
:func:`curses.window.vline` function in :mod:`curses`.

- gh-issue-100472: Remove claim in documentation that the ``stripdir``,
``prependdir`` and ``limit_sl_dest`` parameters of
:func:`compileall.compile_dir` and :func:`compileall.compile_file` could
be :class:`bytes`.

- gh-issue-99931: Use `sphinxext-opengraph
<https://sphinxext-opengraph.readthedocs.io/>`__ to generate `OpenGraph
metadata <https://ogp.me/>`__.

Tests
-----

- gh-issue-101334: ``test_tarfile`` has been updated to pass when run as a
high UID.

- gh-issue-100454: Start running SSL tests with OpenSSL 3.1.0-beta1.

- gh-issue-96002: Add functional test for Argument Clinic.

Build
-----

- gh-issue-101522: Allow overriding Windows dependencies versions and paths
using MSBuild properties.

Windows
-------

- gh-issue-101543: Ensure the install path in the registry is only used when
the standard library hasn't been located in any other way.

- gh-issue-101467: The ``py.exe`` launcher now correctly filters when only a
single runtime is installed. It also correctly handles prefix matches on
tags so that ``-3.1`` does not match ``3.11``, but would still match
``3.1-32``.

- gh-issue-101135: Restore ability to launch older 32-bit versions from the
:file:`py.exe` launcher when both 32-bit and 64-bit installs of the same
version are available.

- gh-issue-82052: Fixed an issue where writing more than 32K of Unicode
output to the console screen in one go can result in mojibake.

- gh-issue-100320: Ensures the ``PythonPath`` registry key from an install
is used when launching from a different copy of Python that relies on an
existing install to provide a copy of its modules and standard library.

- gh-issue-100247: Restores support for the :file:`py.exe` launcher finding
shebang commands in its configuration file using the full command name.

- gh-issue-100180: Update Windows installer to OpenSSL 1.1.1s

- bpo-43984: :meth:`winreg.SetValueEx` now leaves the target value untouched
in the case of conversion errors. Previously, ``-1`` would be written in
case of such errors.

macOS
-----

- gh-issue-100180: Update macOS installer to OpenSSL 1.1.1s

Tools/Demos
-----------

- bpo-45256: Fix a bug that caused an :exc:`AttributeError` to be raised in
``python-gdb.py`` when ``py-locals`` is used without a frame.

- gh-issue-100342: Add missing ``NULL`` check for possible allocation
failure in ``*args`` parsing in Argument Clinic.

- gh-issue-64490: Argument Clinic varargs bugfixes

* Fix out-of-bounds error in :c:func:`!_PyArg_UnpackKeywordsWithVararg`.
* Fix incorrect check which allowed more than one varargs in clinic.py.
* Fix miscalculation of ``noptargs`` in generated code.
* Do not generate ``noptargs`` when there is a vararg argument and no optional argument.

C API
-----

- gh-issue-99240: In argument parsing, after deallocating newly allocated
memory, reset its pointer to NULL.

What's New in Python 3.11.1 final?
==================================

*Release date: 2022-12-06*

Security
--------

- gh-issue-100001: ``python -m http.server`` no longer allows terminal
control characters sent within a garbage request to be printed to the
stderr server log.

This is done by changing the :mod:`http.server`
:class:`BaseHTTPRequestHandler` ``.log_message`` method to replace control
characters with a ``\xHH`` hex escape before printing.

- gh-issue-87604: Avoid publishing list of active per-interpreter audit
hooks via the :mod:`gc` module

- gh-issue-98433: The IDNA codec decoder used on DNS hostnames by
:mod:`socket` or :mod:`asyncio` related name resolution functions no
longer involves a quadratic algorithm. This prevents a potential CPU
denial of service if an out-of-spec excessive length hostname involving
bidirectional characters were decoded. Some protocols such as
:mod:`urllib` http ``3xx`` redirects potentially allow for an attacker to
supply such a name.

- gh-issue-98739: Update bundled libexpat to 2.5.0

- gh-issue-97612: Fix a shell code injection vulnerability in the
``get-remote-certificate.py`` example script. The script no longer uses a
shell to run ``openssl`` commands. Issue reported and initial fix by Caleb
Shortt. Patch by Victor Stinner.

Core and Builtins
-----------------

- gh-issue-99886: Fix a crash when an object which does not have a
dictionary frees its instance values.

- gh-issue-99891: Fix a bug in the tokenizer that could cause infinite
recursion when showing syntax warnings that happen in the first line of
the source. Patch by Pablo Galindo

- gh-issue-99729: Fix an issue that could cause frames to be visible to
Python code as they are being torn down, possibly leading to memory
corruption or hard crashes of the interpreter.

- gh-issue-99578: Fix a reference bug in :func:`_imp.create_builtin()` after
the creation of the first sub-interpreter for modules ``builtins`` and
``sys``. Patch by Victor Stinner.

- gh-issue-99581: Fixed a bug that was causing a buffer overflow if the
tokenizer copies a line missing the newline caracter from a file that is
as long as the available tokenizer buffer. Patch by Pablo galindo

- gh-issue-99553: Fix bug where an :exc:`ExceptionGroup` subclass can wrap a
:exc:`BaseException`.

- gh-issue-99370: Fix zip path for venv created from a non-installed python
on POSIX platforms.

- gh-issue-99298: Fix an issue that could potentially cause incorrect error
handling for some bytecode instructions.

- gh-issue-99205: Fix an issue that prevented :c:type:`PyThreadState` and
:c:type:`PyInterpreterState` memory from being freed properly.

- gh-issue-99181: Fix failure in :keyword:`except* <except_star>` with
unhashable exceptions.

- gh-issue-99204: Fix calculation of :data:`sys._base_executable` when
inside a POSIX virtual environment using copies of the python binary when
the base installation does not provide the executable name used by the
venv. Calculation will fall back to alternative names ("python<MAJOR>",
"python<MAJOR>.<MINOR>").

- gh-issue-96055: Update :mod:`faulthandler` to emit an error message with
the proper unexpected signal number. Patch by Dong-hee Na.

- gh-issue-99153: Fix location of :exc:`SyntaxError` for a :keyword:`try`
block with both :keyword:`except` and :keyword:`except* <except_star>`.

- gh-issue-99103: Fix the error reporting positions of specialized traceback
anchors when the source line contains Unicode characters.

- gh-issue-98852: Fix subscription of type aliases containing bare generic
types or types like :class:`~typing.TypeVar`: for example ``tuple[A,
T][int]`` and ``tuple[TypeVar, T][int]``, where ``A`` is a generic type,
and ``T`` is a type variable.

- gh-issue-98925: Lower the recursion depth for marshal on WASI to support
wasmtime 2.0/main.

- gh-issue-98783: Fix multiple crashes in debug mode when ``str`` subclasses
are used instead of ``str`` itself.

- gh-issue-99257: Fix an issue where member descriptors (such as those for
:attr:`~object.__slots__`) could behave incorrectly or crash instead of
raising a :exc:`TypeError` when accessed via an instance of an invalid
type.

- gh-issue-98374: Suppress ImportError for invalid query for help() command.
Patch by Dong-hee Na.

- gh-issue-98415: Fix detection of MAC addresses for :mod:`uuid` on certain
OSs. Patch by Chaim Sanders

- gh-issue-92119: Print exception class name instead of its string
representation when raising errors from :mod:`ctypes` calls.

- gh-issue-96078: :func:`os.sched_yield` now release the GIL while calling
sched_yield(2). Patch by Dong-hee Na.

- gh-issue-93354: Fix an issue that could delay the specialization of
:opcode:`PRECALL` instructions.

- gh-issue-97943: Bugfix: :func:`PyFunction_GetAnnotations` should return a
borrowed reference. It was returning a new reference.

- gh-issue-97779: Ensure that all Python frame objects are backed by
"complete" frames.

- gh-issue-97591: Fixed a missing incref/decref pair in
``Exception.__setstate__()``. Patch by Ofey Chan.

- gh-issue-94526: Fix the Python path configuration used to initialized
:data:`sys.path` at Python startup. Paths are no longer encoded to
UTF-8/strict to avoid encoding errors if it contains surrogate characters
(bytes paths are decoded with the surrogateescape error handler). Patch by
Victor Stinner.

- gh-issue-95921: Fix overly-broad source position information for chained
comparisons used as branching conditions.

- gh-issue-96387: At Python exit, sometimes a thread holding the GIL can
wait forever for a thread (usually a daemon thread) which requested to
drop the GIL, whereas the thread already exited. To fix the race
condition, the thread which requested the GIL drop now resets its request
before exiting. Issue discovered and analyzed by Mingliang ZHAO. Patch by
Victor Stinner.

- gh-issue-96864: Fix a possible assertion failure, fatal error, or
:exc:`SystemError` if a line tracing event raises an exception while
opcode tracing is enabled.

- gh-issue-96678: Fix undefined behaviour in C code of null pointer
arithmetic.

- gh-issue-96754: Make sure that all frame objects created are created from
valid interpreter frames. Prevents the possibility of invalid frames in
backtraces and signal handlers.

- gh-issue-95196: Disable incorrect pickling of the C implemented
classmethod descriptors.

- gh-issue-96005: On WASI :data:`~errno.ENOTCAPABLE` is now mapped to
:exc:`PermissionError`. The :mod:`errno` modules exposes the new error
number. ``getpath.py`` now ignores :exc:`PermissionError` when it cannot
open landmark files ``pybuilddir.txt`` and ``pyenv.cfg``.

- gh-issue-93696: Allow :mod:`pdb` to locate source for frozen modules in
the standard library.

- bpo-31718: Raise :exc:`ValueError` instead of :exc:`SystemError` when
methods of uninitialized :class:`io.IncrementalNewlineDecoder` objects are
called. Patch by Oren Milman.

- bpo-38031: Fix a possible assertion failure in :class:`io.FileIO` when the
opener returns an invalid file descriptor.

Library
-------

- gh-issue-100001: Also \ escape \s in the http.server
BaseHTTPRequestHandler.log_message so that it is technically possible to
parse the line and reconstruct what the original data was. Without this a
\xHH is ambiguious as to if it is a hex replacement we put in or the
characters r"\x" came through in the original request line.

- gh-issue-93453: :func:`asyncio.get_event_loop` now only emits a
deprecation warning when a new event loop was created implicitly. It no
longer emits a deprecation warning if the current event loop was set.

- gh-issue-51524: Fix bug when calling trace.CoverageResults with valid
infile.

- gh-issue-99645: Fix a bug in handling class cleanups in
:class:`unittest.TestCase`. Now ``addClassCleanup()`` uses separate lists
for different ``TestCase`` subclasses, and ``doClassCleanups()`` only
cleans up the particular class.

- gh-issue-97001: Release the GIL when calling termios APIs to avoid
blocking threads.

- gh-issue-99341: Fix :func:`ast.increment_lineno` to also cover
:class:`ast.TypeIgnore` when changing line numbers.

- gh-issue-99418: Fix bug in :func:`urllib.parse.urlparse` that causes URL
schemes that begin with a digit, a plus sign, or a minus sign to be parsed
incorrectly.

- gh-issue-99382: Check the number of arguments in substitution in user
generics containing a :class:`~typing.TypeVarTuple` and one or more
:class:`~typing.TypeVar`.

- gh-issue-99379: Fix substitution of :class:`~typing.ParamSpec` followed by
:class:`~typing.TypeVarTuple` in generic aliases.

- gh-issue-99344: Fix substitution of :class:`~typing.TypeVarTuple` and
:class:`~typing.ParamSpec` together in user generics.

- gh-issue-74044: Fixed bug where :func:`inspect.signature` reported
incorrect arguments for decorated methods.

- gh-issue-99275: Fix ``SystemError`` in :mod:`ctypes` when exception was
not set during ``__initsubclass__``.

- gh-issue-99277: Remove older version of
``_SSLProtocolTransport.get_write_buffer_limits`` in
:mod:`!asyncio.sslproto`

- gh-issue-99248: fix negative numbers failing in verify()

- gh-issue-99155: Fix :class:`statistics.NormalDist` pickle with ``0`` and
``1`` protocols.

- gh-issue-93464: ``enum.auto()`` is now correctly activated when combined
with other assignment values. E.g. ``ONE = auto(), 'some text'`` will now
evaluate as ``(1, 'some text')``.

- gh-issue-99134: Update the bundled copy of pip to version 22.3.1.

- gh-issue-83004: Clean up refleak on failed module initialisation in
:mod:`_zoneinfo`

- gh-issue-83004: Clean up refleaks on failed module initialisation in in
:mod:`_pickle`

- gh-issue-83004: Clean up refleak on failed module initialisation in
:mod:`_io`.

- gh-issue-98897: Fix memory leak in :func:`math.dist` when both points
don't have the same dimension. Patch by Kumar Aditya.

- gh-issue-98706: [3.11] Applied changes from importlib_metadata `4.11.4
through 4.13
<https://importlib-metadata.readthedocs.io/en/latest/history.html#v4-13-0>`_,
including compatibility and robustness fixes for ``Distribution`` objects
without ``_normalized_name``, disallowing invalid inputs to
``Distribution.from_name``, and refined behaviors in
``PathDistribution._name_from_stem`` and
``PathDistribution._normalized_name``.

- gh-issue-98793: Fix argument typechecks in :func:`!_overlapped.WSAConnect`
and :func:`!_overlapped.Overlapped.WSASendTo` functions.

- gh-issue-98744: Prevent crashing in :mod:`traceback` when retrieving the
byte-offset for some source files that contain certain unicode characters.

- gh-issue-98740: Fix internal error in the :mod:`re` module which in very
rare circumstances prevented compilation of a regular expression
containing a :ref:`conditional expression <re-conditional-expression>`
without the "else" branch.

- gh-issue-98703: Fix :meth:`asyncio.StreamWriter.drain` to call
``protocol.connection_lost`` callback only once on Windows.

- gh-issue-98624: Add a mutex to unittest.mock.NonCallableMock to protect
concurrent access to mock attributes.

- gh-issue-89237: Fix hang on Windows in ``subprocess.wait_closed()`` in
:mod:`asyncio` with :class:`~asyncio.ProactorEventLoop`. Patch by Kumar
Aditya.

- gh-issue-98458: Fix infinite loop in unittest when a self-referencing
chained exception is raised

- gh-issue-97928: :meth:`tkinter.Text.count` raises now an exception for
options starting with "-" instead of silently ignoring them.

- gh-issue-97966: On ``uname_result``, restored expectation that ``_fields``
and ``_asdict`` would include all six properties including ``processor``.

- gh-issue-98307: A :meth:`~logging.handlers.SysLogHandler.createSocket`
method was added to :class:`~logging.handlers.SysLogHandler`.

- gh-issue-96035: Fix bug in :func:`urllib.parse.urlparse` that causes
certain port numbers containing whitespace, underscores, plus and minus
signs, or non-ASCII digits to be incorrectly accepted.

- gh-issue-98251: Allow :mod:`venv` to pass along :envvar:`PYTHON*`
variables to ``ensurepip`` and ``pip`` when they do not impact path
resolution

- gh-issue-98178: On macOS, fix a crash in :func:`syslog.syslog` in
multi-threaded applications. On macOS, the libc ``syslog()`` function is
not thread-safe, so :func:`syslog.syslog` no longer releases the GIL to
call it. Patch by Victor Stinner.

- gh-issue-96151: Allow ``BUILTINS`` to be a valid field name for frozen
dataclasses.

- gh-issue-87730: Wrap network errors consistently in urllib FTP support, so
the test suite doesn't fail when a network is available but the public
internet is not reachable.

- gh-issue-98086: Make sure ``patch.dict()`` can be applied on async
functions.

- gh-issue-90985: Earlier in 3.11 we deprecated
``asyncio.Task.cancel("message")``. We realized we were too harsh, and
have undeprecated it.

- gh-issue-97837: Change deprecate warning message in :mod:`unittest` from

``It is deprecated to return a value!=None``

``It is deprecated to return a value that is not None from a test case``

- gh-issue-97825: Fixes :exc:`AttributeError` when
:meth:`subprocess.check_output` is used with argument ``input=None`` and
either of the arguments *encoding* or *errors* are used.

- gh-issue-82836: Fix :attr:`~ipaddress.IPv4Address.is_private` properties
in the :mod:`ipaddress` module. Previously non-private networks
(0.0.0.0/0) would return True from this method; now they correctly return
False.

- gh-issue-96827: Avoid spurious tracebacks from :mod:`asyncio` when default
executor cleanup is delayed until after the event loop is closed (e.g. as
the result of a keyboard interrupt).

- gh-issue-97592: Avoid a crash in the C version of
:meth:`asyncio.Future.remove_done_callback` when an evil argument is
passed.

- gh-issue-97639: Remove ``tokenize.NL`` check from :mod:`tabnanny`.

- gh-issue-73588: Fix generation of the default name of
:class:`tkinter.Checkbutton`. Previously, checkbuttons in different parent
widgets could have the same short name and share the same state if
arguments "name" and "variable" are not specified. Now they are globally
unique.

- gh-issue-97005: Update bundled libexpat to 2.4.9

- gh-issue-85760: Fix race condition in :mod:`asyncio` where
:meth:`~asyncio.SubprocessProtocol.process_exited` called before the
:meth:`~asyncio.SubprocessProtocol.pipe_data_received` leading to
inconsistent output. Patch by Kumar Aditya.

- gh-issue-96819: Fixed check in :mod:`multiprocessing.resource_tracker`
that guarantees that the length of a write to a pipe is not greater than
``PIPE_BUF``.

- gh-issue-96741: Corrected type annotation for dataclass attribute
``pstats.FunctionProfile.ncalls`` to be ``str``.

- gh-issue-95987: Fix ``repr`` of ``Any`` subclasses.

- gh-issue-96388: Work around missing socket functions in
:class:`~socket.socket`'s ``__repr__``.

- gh-issue-96073: In :mod:`inspect`, fix overeager replacement of
"``typing.``" in formatting annotations.

- gh-issue-96192: Fix handling of ``bytes`` :term:`path-like objects
<path-like object>` in :func:`os.ismount()`.

- gh-issue-96052: Fix handling compiler warnings (SyntaxWarning and
DeprecationWarning) in :func:`codeop.compile_command` when checking for
incomplete input. Previously it emitted warnings and raised a SyntaxError.
Now it always returns ``None`` for incomplete input without emitting any
warnings.

- gh-issue-88863: To avoid apparent memory leaks when
:func:`asyncio.open_connection` raises, break reference cycles generated
by local exception and future instances (which has exception instance as
its member var). Patch by Dong Uk, Kang.

- gh-issue-91212: Fixed flickering of the turtle window when the tracer is
turned off. Patch by Shin-myoung-serp.

- gh-issue-88050: Fix :mod:`asyncio` subprocess transport to kill process
cleanly when process is blocked and avoid ``RuntimeError`` when loop is
closed. Patch by Kumar Aditya.

- gh-issue-93858: Prevent error when activating venv in nested fish
instances.

- gh-issue-91078: :meth:`TarFile.next` now returns ``None`` when called on
an empty tarfile.

- bpo-47220: Document the optional *callback* parameter of
:class:`WeakMethod`. Patch by Géry Ogam.

- bpo-46364: Restrict use of sockets instead of pipes for stdin of
subprocesses created by :mod:`asyncio` to AIX platform only.

- bpo-38523: :func:`shutil.copytree` now applies the
*ignore_dangling_symlinks* argument recursively.

- bpo-36267: Fix IndexError in :class:`argparse.ArgumentParser` when a
``store_true`` action is given an explicit argument.

Documentation
-------------

- gh-issue-92892: Document that calling variadic functions with ctypes
requires special care on macOS/arm64 (and possibly other platforms).

- gh-issue-85525: Remove extra row

- gh-issue-95588: Clarified the conflicting advice given in the :mod:`ast`
documentation about :func:`ast.literal_eval` being "safe" for use on
untrusted input while at the same time warning that it can crash the
process. The latter statement is true and is deemed unfixable without a
large amount of work unsuitable for a bugfix. So we keep the warning and
no longer claim that ``literal_eval`` is safe.

- bpo-41825: Restructured the documentation for the :func:`os.wait*
<os.wait>` family of functions, and improved the docs for
:func:`os.waitid` with more explanation of the possible argument
constants.

Tests
-----

- gh-issue-99892: Skip test_normalization() of test_unicodedata if it fails
to download NormalizationTest.txt file from pythontest.net. Patch by
Victor Stinner.

- gh-issue-99934: Correct test_marsh on (32 bit) x86: test_deterministic
sets was failing.

- gh-issue-99659: Optional big memory tests in ``test_sqlite3`` now catch
the correct :exc:`sqlite.DataError` exception type in case of too large
strings and/or blobs passed.

- gh-issue-98713: Fix a bug in the :mod:`typing` tests where a test relying
on CPython-specific implementation details was not decorated with
``@cpython_only`` and was not skipped on other implementations.

- gh-issue-87390: Add tests for star-unpacking with PEP 646, and some other
miscellaneous PEP 646 tests.

- gh-issue-96853: Added explicit coverage of ``Py_Initialize`` (and hence
``Py_InitializeEx``) back to the embedding tests (all other embedding
tests migrated to ``Py_InitializeFromConfig`` in Python 3.11)

- bpo-34272: Some C API tests were moved into the new Lib/test/test_capi/
directory.

Build
-----

- gh-issue-99086: Fix ``-Wimplicit-int``, ``-Wstrict-prototypes``, and
``-Wimplicit-function-declaration`` compiler warnings in
:program:`configure` checks.

- gh-issue-99337: Fix a compilation issue with GCC 12 on macOS.

- gh-issue-99086: Fix ``-Wimplicit-int`` compiler warning in
:program:`configure` check for ``PTHREAD_SCOPE_SYSTEM``.

- gh-issue-98872: Fix a possible fd leak in ``Programs/_freeze_module.c``
introduced in Python 3.11.

- gh-issue-99016: Fix build with ``PYTHON_FOR_REGEN=python3.8``.

- gh-issue-97731: Specify the full path to the source location for ``make
docclean`` (needed for cross-builds).

- gh-issue-98707: Don't use vendored ``libmpdec`` headers if
:option:`--with-system-libmpdec` is passed to :program:`configure`. Don't
use vendored ``libexpat`` headers if :option:`--with-system-expat` is
passed to :program:`!configure`.

- gh-issue-96761: Fix the build process of clang compiler for
:program:`_bootstrap_python` if LTO optimization is applied. Patch by
Matthias Görgens and Dong-hee Na.

- gh-issue-96883: ``wasm32-emscripten`` builds for browsers now include
:mod:`concurrent.futures` for :mod:`asyncio` and :mod:`unittest.mock`.

- gh-issue-84461: ``wasm32-emscripten`` platform no longer builds
:mod:`resource` module, :func:`~os.getresuid`, :func:`~os.getresgid`, and
their setters. The APIs are stubs and not functional.

- gh-issue-94280: Updated pegen regeneration script on Windows to find and
use Python 3.9 or higher. Prior to this, pegen regeneration already
required 3.9 or higher, but the script may have used lower versions of
Python.

Windows
-------

- gh-issue-99345: Use faster initialization functions to detect install
location for Windows Store package

- gh-issue-98629: Fix initialization of :data:`sys.version` and ``sys._git``
on Windows

- gh-issue-99442: Fix handling in :ref:`launcher` when ``argv[0]`` does not
include a file extension.

- gh-issue-98689: Update Windows builds to zlib v1.2.13. v1.2.12 has
CVE-2022-37434, but the vulnerable ``inflateGetHeader`` API is not used by
Python.

- gh-issue-98790: Assumes that a missing ``DLLs`` directory means that
standard extension modules are in the executable's directory.

- gh-issue-98745: Update :file:`py.exe` launcher to install 3.11 by default
and 3.12 on request.

- gh-issue-98692: Fix the :ref:`launcher` ignoring unrecognized shebang
lines instead of treating them as local paths

- gh-issue-94328: Update Windows installer to use SQLite 3.39.4.

- gh-issue-97728: Fix possible crashes caused by the use of uninitialized
variables when pass invalid arguments in :func:`os.system` on Windows and
in Windows-specific modules (like ``winreg``).

- gh-issue-96965: Update libffi to 3.4.3

- gh-issue-94781: Fix :file:`pcbuild.proj` to clean previous instances of
ouput files in ``Python\deepfreeze`` and ``Python\frozen_modules``
directories on Windows. Patch by Charlie Zhao.

- bpo-40882: Fix a memory leak in
:class:`multiprocessing.shared_memory.SharedMemory` on Windows.

macOS
-----

- gh-issue-87235: On macOS ``python3 /dev/fd/9 9</path/to/script.py`` failed
for any script longer than a couple of bytes.

- gh-issue-98940: Fix ``Mac/Extras.install.py`` file filter bug.

- gh-issue-94328: Update macOS installer to SQLite 3.39.4.

IDLE
----

- gh-issue-97527: Fix a bug in the previous bugfix that caused IDLE to not
start when run with 3.10.8, 3.12.0a1, and at least Microsoft Python
3.10.2288.0 installed without the Lib/test package. 3.11.0 was never
affected.

Tools/Demos
-----------

- gh-issue-95853: The ``wasm_build.py`` script now pre-builds Emscripten
ports, checks for broken EMSDK versions, and warns about pkg-config env
vars.

- gh-issue-95853: The new tool ``Tools/wasm/wasm_builder.py`` automates
configure, compile, and test steps for building CPython on WebAssembly
platforms.

- gh-issue-95731: Fix handling of module docstrings in
:file:`Tools/i18n/pygettext.py`.

C API
-----

- gh-issue-98680: ``PyBUF_*`` constants were marked as part of Limited API
of Python 3.11+. These were available in 3.11.0 with
:c:macro:`Py_LIMITED_API` defined for 3.11, and are necessary to use the
buffer API.

- gh-issue-98978: Fix use-after-free in ``Py_SetPythonHome(NULL)``,
``Py_SetProgramName(NULL)`` and ``_Py_SetProgramFullPath(NULL)`` function
calls. Issue reported by Benedikt Reinartz. Patch by Victor Stinner.

- gh-issue-96853: ``Py_InitializeEx`` now correctly calls ``PyConfig_Clear``
after initializing the interpreter (the omission didn't cause a memory
leak only because none of the dynamically allocated config fields are
populated by the wrapper function)

What's New in Python 3.11.0 final?
==================================

*Release date: 2022-10-24*

Security
--------

- gh-issue-97616: Fix multiplying a list by an integer (``list *= int``):
detect the integer overflow when the new allocated length is close to the
maximum size. Issue reported by Jordan Limor. Patch by Victor Stinner.

- gh-issue-97514: On Linux the :mod:`multiprocessing` module returns to
using filesystem backed unix domain sockets for communication with the
*forkserver* process instead of the Linux abstract socket namespace. Only
code that chooses to use the :ref:`"forkserver" start method
<multiprocessing-start-methods>` is affected.

Abstract sockets have no permissions and could allow any user on the
system in the same `network namespace
<https://man7.org/linux/man-pages/man7/network_namespaces.7.html>`_ (often
the whole system) to inject code into the multiprocessing *forkserver*
process. This was a potential privilege escalation. Filesystem based
socket permissions restrict this to the *forkserver* process user as was
the default in Python 3.8 and earlier.

This prevents Linux `CVE-2022-42919
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-42919>`_.

Core and Builtins
-----------------

- gh-issue-97002: Fix an issue where several frame objects could be backed
by the same interpreter frame, possibly leading to corrupted memory and
hard crashes of the interpreter.

- gh-issue-97752: Fix possible data corruption or crashes when accessing the
``f_back`` member of newly-created generator or coroutine frames.

- gh-issue-96975: Fix a crash occurring when :c:func:`PyEval_GetFrame` is
called while the topmost Python frame is in a partially-initialized state.

- gh-issue-96848: Fix command line parsing: reject :option:`-X
int_max_str_digits <-X>` option with no value (invalid) when the
:envvar:`PYTHONINTMAXSTRDIGITS` environment variable is set to a valid
limit. Patch by Victor Stinner.

- gh-issue-96821: Fix undefined behaviour in ``_testcapimodule.c``.

- gh-issue-95778: When :exc:`ValueError` is raised if an integer is larger
than the limit, mention the :func:`sys.set_int_max_str_digits` function in
the error message. Patch by Victor Stinner.

- gh-issue-96587: Correctly raise ``SyntaxError`` on exception groups
(:pep:`654`) on python versions prior to 3.11

- bpo-42316: Document some places where an assignment expression needs
parentheses.

Library
-------

- gh-issue-98331: Update the bundled copies of pip and setuptools to
versions 22.3 and 65.5.0 respectively.

- gh-issue-90985: Earlier in 3.11 we deprecated
``asyncio.Task.cancel("message")``. We realized we were too harsh, and
have undeprecated it.

- gh-issue-97545: Make Semaphore run faster.

- gh-issue-96865: fix Flag to use boundary CONFORM

This restores previous Flag behavior of allowing flags with non-sequential
values to be combined; e.g.

class Skip(Flag): TWO = 2 EIGHT = 8

Skip.TWO | Skip.EIGHT -> <Skip.TWO|EIGHT: 10>

- gh-issue-90155: Fix broken :class:`asyncio.Semaphore` when acquire is
cancelled.

Documentation
-------------

- gh-issue-97741: Fix ``!`` in c domain ref target syntax via a ``conf.py``
patch, so it works as intended to disable ref target resolution.

- gh-issue-93031: Update tutorial introduction output to use 3.10+
SyntaxError invalid range.

Tests
-----

- gh-issue-95027: On Windows, when the Python test suite is run with the
``-jN`` option, the ANSI code page is now used as the encoding for the
stdout temporary file, rather than using UTF-8 which can lead to decoding
errors. Patch by Victor Stinner.

Build
-----

- gh-issue-96729: Ensure that Windows releases built with
``Tools\msi\buildrelease.bat`` are upgradable to and from official Python
releases.

Windows
-------

- gh-issue-98360: Fixes :mod:`multiprocessing` spawning child processes on
Windows from a virtual environment to ensure that child processes that
also use :mod:`multiprocessing` to spawn more children will recognize that
they are in a virtual environment.

- gh-issue-98414: Fix :file:`py.exe` launcher handling of ``-V:<company>/``
option when default preferences have been set in environment variables or
configuration files.

- gh-issue-90989: Clarify some text in the Windows installer.

macOS
-----

- gh-issue-97897: The macOS 13 SDK includes support for the ``mkfifoat`` and
``mknodat`` system calls. Using the ``dir_fd`` option with either
:func:`os.mkfifo` or :func:`os.mknod` could result in a segfault if
cpython is built with the macOS 13 SDK but run on an earlier version of
macOS. Prevent this by adding runtime support for detection of these
system calls ("weaklinking") as is done for other newer syscalls on macOS.

What's New in Python 3.11.0 release candidate 2?
================================================

*Release date: 2022-09-11*

Security
--------

- gh-issue-95778: Converting between :class:`int` and :class:`str` in bases
other than 2 (binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base
10 (decimal) now raises a :exc:`ValueError` if the number of digits in
string form is above a limit to avoid potential denial of service attacks
due to the algorithmic complexity. This is a mitigation for
`CVE-2020-10735
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735>`_.

This new limit can be configured or disabled by environment variable,
command line flag, or :mod:`sys` APIs. See the :ref:`integer string
conversion length limitation <int_max_str_digits>` documentation. The
default limit is 4300 digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with
feedback from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and
Mark Dickinson.

Core and Builtins
-----------------

- gh-issue-96678: Fix case of undefined behavior in ceval.c

- gh-issue-96641: Do not expose ``KeyWrapper`` in :mod:`_functools`.

- gh-issue-96636: Ensure that tracing, ``sys.setrace()``, is turned on
immediately. In pre-release versions of 3.11, some tracing events might
have been lost when turning on tracing in a ``__del__`` method or
interrupt.

- gh-issue-96572: Fix use after free in trace refs build mode. Patch by
Kumar Aditya.

- gh-issue-96611: When loading a file with invalid UTF-8 inside a multi-line
string, a correct SyntaxError is emitted.

- gh-issue-96612: Make sure that incomplete frames do not show up in
tracemalloc traces.

- gh-issue-96569: Remove two cases of undefined behavior, by adding NULL
checks.

- gh-issue-96582: Fix possible ``NULL`` pointer dereference in
``_PyThread_CurrentFrames``. Patch by Kumar Aditya.

- gh-issue-96352: Fix :exc:`AttributeError` missing ``name`` and ``obj``
attributes in :meth:`object.__getattribute__`. Patch by Philip Georgi.

- gh-issue-96268: Loading a file with invalid UTF-8 will now report the
broken character at the correct location.

- gh-issue-96187: Fixed a bug that caused ``_PyCode_GetExtra`` to return
garbage for negative indexes. Patch by Pablo Galindo

- gh-issue-96071: Fix a deadlock in :c:func:`PyGILState_Ensure` when
allocating new thread state. Patch by Kumar Aditya.

- gh-issue-96046: :c:func:`PyType_Ready` now initializes ``ht_cached_keys``
and performs additional checks to ensure that type objects are properly
configured. This avoids crashes in 3rd party packages that don't use
regular API to create new types.

- gh-issue-95818: Skip over incomplete frames in
:c:func:`PyThreadState_GetFrame`.

- gh-issue-95876: Fix format string in
``_PyPegen_raise_error_known_location`` that can lead to memory corruption
on some 64bit systems. The function was building a tuple with ``i`` (int)
instead of ``n`` (Py_ssize_t) for Py_ssize_t arguments.

- gh-issue-95605: Fix misleading contents of error message when converting
an all-whitespace string to :class:`float`.

- gh-issue-94996: :func:`ast.parse` will no longer parse function
definitions with positional-only params when passed ``feature_version``
less than ``(3, 8)``. Patch by Shantanu Jain.

Library
-------

- gh-issue-96700: Fix incorrect error message in the :mod:`io` module.

- gh-issue-96652: Fix the faulthandler implementation of
``faulthandler.register(signal, chain=True)`` if the ``sigaction()``
function is not available: don't call the previous signal handler if it's
NULL. Patch by Victor Stinner.

- gh-issue-68163: Correct conversion of :class:`numbers.Rational`'s to
:class:`float`.

- gh-issue-96385: Fix ``TypeVarTuple.__typing_prepare_subst__``.
``TypeError`` was not raised when using more than one ``TypeVarTuple``,
like ``[*T, *V]`` in type alias substitutions.

- gh-issue-90467: Fix :class:`asyncio.streams.StreamReaderProtocol` to keep
a strong reference to the created task, so that it's not garbage collected

- gh-issue-96159: Fix a performance regression in logging
TimedRotatingFileHandler. Only check for special files when the rollover
time has passed.

- gh-issue-96175: Fix unused ``localName`` parameter in the ``Attr`` class
in :mod:`xml.dom.minidom`.

- gh-issue-96125: Fix incorrect condition that causes
``sys.thread_info.name`` to be wrong on pthread platforms.

- gh-issue-95463: Remove an incompatible change from :issue:`28080` that
caused a regression that ignored the utf8 in ``ZipInfo.flag_bits``. Patch
by Pablo Galindo.

- gh-issue-95899: Fix :class:`asyncio.Runner` to call
:func:`asyncio.set_event_loop` only once to avoid calling
:meth:`~asyncio.AbstractChildWatcher.attach_loop` multiple times on child
watchers. Patch by Kumar Aditya.

- gh-issue-95736: Fix :class:`unittest.IsolatedAsyncioTestCase` to set event
loop before calling setup functions. Patch by Kumar Aditya.

- gh-issue-95704: When a task catches :exc:`asyncio.CancelledError` and
raises some other error, the other error should generally not silently be
suppressed.

- gh-issue-95231: Fail gracefully if :data:`~errno.EPERM` or
:data:`~errno.ENOSYS` is raised when loading :mod:`crypt` methods. This
may happen when trying to load ``MD5`` on a Linux kernel with :abbr:`FIPS
(Federal Information Processing Standard)` enabled.

- gh-issue-74116: Allow :meth:`asyncio.StreamWriter.drain` to be awaited
concurrently by multiple tasks. Patch by Kumar Aditya.

- gh-issue-92986: Fix :func:`ast.unparse` when ``ImportFrom.level`` is None

Documentation
-------------

- gh-issue-96098: Improve discoverability of the higher level
concurrent.futures module by providing clearer links from the lower level
threading and multiprocessing modules.

- gh-issue-95957: What's New 3.11 now has instructions for how to provide
compiler and linker flags for Tcl/Tk and OpenSSL on RHEL 7 and CentOS 7.

Tests
-----

- gh-issue-95243: Mitigate the inherent race condition from using
find_unused_port() in testSockName() by trying to find an unused port a
few times before failing. Patch by Ross Burton.

Build
-----

- gh-issue-94682: Build and test with OpenSSL 1.1.1q

Windows
-------

- gh-issue-96577: Fixes a potential buffer overrun in :mod:`msilib`.

- gh-issue-96559: Fixes the Windows launcher not using the compatible
interpretation of default tags found in configuration files when no tag
was passed to the command.

What's New in Python 3.11.0 release candidate 1?
================================================

*Release date: 2022-08-05*

Core and Builtins
-----------------

- gh-issue-95150: Update code object hashing and equality to consider all
debugging and exception handling tables. This fixes an issue where certain
non-identical code objects could be "deduplicated" during compilation.

- gh-issue-95355: ``_PyPegen_Parser_New`` now properly detects token memory
allocation errors. Patch by Honglin Zhu.

- gh-issue-90081: Run Python code in tracer/profiler function at full speed.
Fixes slowdown in earlier versions of 3.11.

- gh-issue-95324: Emit a warning in debug mode if an object does not call
:c:func:`PyObject_GC_UnTrack` before deallocation. Patch by Pablo Galindo.

- gh-issue-95185: Prevented crashes in the AST constructor when compiling
some absurdly long expressions like ``"+0"*1000000``.
:exc:`RecursionError` is now raised instead. Patch by Pablo Galindo

- gh-issue-93351: :class:`ast.AST` node positions are now validated when
provided to :func:`compile` and other related functions. If invalid
positions are detected, a :exc:`ValueError` will be raised.

- gh-issue-94938: Fix error detection in some builtin functions when keyword
argument name is an instance of a str subclass with overloaded ``__eq__``
and ``__hash__``. Previously it could cause SystemError or other undesired
behavior.

Library
-------

- gh-issue-95609: Update bundled pip to 22.2.2.

- gh-issue-95289: Fix :class:`asyncio.TaskGroup` to propagate exception when
:exc:`asyncio.CancelledError` was replaced with another exception by a
context manger. Patch by Kumar Aditya and Guido van Rossum.

- gh-issue-95339: Update bundled pip to 22.2.1.

- gh-issue-95045: Fix GC crash when deallocating ``_lsprof.Profiler`` by
untracking it before calling any callbacks. Patch by Kumar Aditya.

- gh-issue-95097: Fix :func:`asyncio.run` for :class:`asyncio.Task`
implementations without :meth:`~asyncio.Task.uncancel` method. Patch by
Kumar Aditya.

- gh-issue-93899: Fix check for existence of :data:`os.EFD_CLOEXEC`,
:data:`os.EFD_NONBLOCK` and :data:`os.EFD_SEMAPHORE` flags on older kernel
versions where these flags are not present. Patch by Kumar Aditya.

- gh-issue-95166: Fix :meth:`concurrent.futures.Executor.map` to cancel the
currently waiting on future on an error - e.g. TimeoutError or
KeyboardInterrupt.

- gh-issue-95109: Ensure that timeouts scheduled with
:class:`asyncio.Timeout` that have already expired are delivered promptly.

- gh-issue-91810: Suppress writing an XML declaration in open files in
``ElementTree.write()`` with ``encoding='unicode'`` and
``xml_declaration=None``.

- gh-issue-91447: Fix findtext in the xml module to only give an empty
string when the text attribute is set to None.

Documentation
-------------

- gh-issue-91207: Fix stylesheet not working in Windows CHM htmlhelp docs
and add warning that they are deprecated. Contributed by C.A.M. Gerlach.

- gh-issue-95451: Update library documentation with :ref:`availability
information <wasm-availability>` on WebAssembly platforms
``wasm32-emscripten`` and ``wasm32-wasi``.

- gh-issue-95415: Use consistent syntax for platform availability. The
directive now supports a content body and emits a warning when it
encounters an unknown platform.

- gh-issue-86128: Document a limitation in ThreadPoolExecutor where its exit
handler is executed before any handlers in atexit.

Tests
-----

- gh-issue-95573: :source:`Lib/test/test_asyncio/test_ssl.py` exposed a bug
in the macOS kernel where intense concurrent load on non-blocking sockets
occasionally causes :const:`errno.ENOBUFS` ("No buffer space available")
to be emitted. FB11063974 filed with Apple, in the mean time as a
workaround buffer size used in tests on macOS is decreased to avoid
intermittent failures. Patch by Fantix King.

- gh-issue-95280: Fix problem with ``test_ssl`` ``test_get_ciphers`` on
systems that require perfect forward secrecy (PFS) ciphers.

- gh-issue-94675: Add a regression test for :mod:`re` exponentional slowdown
when using rjsmin.

Build
-----

- gh-issue-94801: Fix a regression in ``configure`` script that caused some
header checks to ignore custom ``CPPFLAGS``. The regression was introduced
in :gh:`94802`.

- gh-issue-95145: wasm32-wasi builds no longer depend on WASIX's pthread
stubs. Python now has its own stubbed pthread API.

- gh-issue-95174: Python now detects missing ``dup`` function in WASI and
works around some missing :mod:`errno`, :mod:`select`, and :mod:`socket`
constants.

- gh-issue-95174: Python now skips missing :mod:`socket` functions and
methods on WASI. WASI can only create sockets from existing fd / accept
and has no netdb.

- gh-issue-95085: Platforms ``wasm32-unknown-emscripten`` and
``wasm32-unknown-wasi`` have been promoted to :pep:`11` tier 3 platform
support.

Windows
-------

- gh-issue-95656: Enable the
:meth:`~sqlite3.Connection.enable_load_extension` :mod:`sqlite3` API.

- gh-issue-95587: Fixes some issues where the Windows installer would
incorrectly detect certain features of an existing install when upgrading.

- gh-issue-94399: Restores the behaviour of :ref:`launcher` for
``/usr/bin/env`` shebang lines, which will now search :envvar:`PATH` for
an executable matching the given command. If none is found, the usual
search process is used.

- gh-issue-95445: Fixes the unsuccessful removal of the HTML document
directory when uninstalling with Windows msi.

- gh-issue-95359: Fix :ref:`launcher` handling of :file:`py.ini` commands
(it was incorrectly expecting a ``py_`` prefix on keys) and crashes when
reading per-user configuration file.

- gh-issue-95285: Fix :ref:`launcher` handling of command lines where it is
only passed a short executable name.

IDLE
----

- gh-issue-65802: Document handling of extensions in Save As dialogs.

- gh-issue-95191: Include prompts when saving Shell (interactive input and
output).

- gh-issue-95511: Fix the Shell context menu copy-with-prompts bug of
copying an extra line when one selects whole lines.

- gh-issue-95471: In the Edit menu, move ``Select All`` and add a new
separator.

- gh-issue-95411: Enable using IDLE's module browser with .pyw files.

- gh-issue-89610: Add .pyi as a recognized extension for IDLE on macOS.
This allows opening stub files by double clicking on them in the Finder.

C API
-----

- gh-issue-92678: Restore the 3.10 behavior for multiple inheritance of C
extension classes that store their dictionary at the end of the struct.

- gh-issue-94936: Added :c:func:`PyCode_GetVarnames`,
:c:func:`PyCode_GetCellvars` and :c:func:`PyCode_GetFreevars` for
accessing ``co_varnames``, ``co_cellvars`` and ``co_freevars``
respectively via the C API.

What's New in Python 3.11.0 beta 5?
===================================

*Release date: 2022-07-25*

Core and Builtins
-----------------

- gh-issue-94438: Fix an issue that caused extended opcode arguments and
some conditional pops to be ignored when calculating valid jump targets
for assignments to the ``f_lineno`` attribute of frame objects. In some
cases, this could cause inconsistent internal state, resulting in a hard
crash of the interpreter.

- gh-issue-95060: Undocumented ``PyCode_Addr2Location`` function now
properly returns when ``addrq`` argument is less than zero.

- gh-issue-95113: Replace all ``EXTENDED_ARG_QUICK`` instructions with basic
:opcode:`EXTENDED_ARG` instructions in unquickened code. Consumers of
non-adaptive bytecode should be able to handle extended arguments the same
way they were handled in CPython 3.10 and older.

- gh-issue-91409: Fix incorrect source location info caused by certain
optimizations in the bytecode compiler.

- gh-issue-94036: Fix incorrect source location info for some multi-line
attribute accesses and method calls.

- gh-issue-94739: Allow jumping within, out of, and across exception
handlers in the debugger.

- gh-issue-94949: :func:`ast.parse` will no longer parse parenthesized
context managers when passed ``feature_version`` less than ``(3, 9)``.
Patch by Shantanu Jain.

- gh-issue-94947: :func:`ast.parse` will no longer parse assignment
expressions when passed ``feature_version`` less than ``(3, 8)``. Patch by
Shantanu Jain.

- gh-issue-91256: Ensures the program name is known for help text during
interpreter startup.

- gh-issue-94869: Fix the column offsets for some expressions in multi-line
f-strings :mod:`ast` nodes. Patch by Pablo Galindo.

- gh-issue-94822: Fix an issue where lookups of metaclass descriptors may be
ignored when an identically-named attribute also exists on the class
itself.

- gh-issue-91153: Fix an issue where a :class:`bytearray` item assignment
could crash if it's resized by the new value's :meth:`__index__` method.

- gh-issue-90699: Fix reference counting bug in :meth:`bool.__repr__`. Patch
by Kumar Aditya.

Library
-------

- gh-issue-95087: Fix IndexError in parsing invalid date in the :mod:`email`
module.

- gh-issue-95199: Upgrade bundled setuptools to 63.2.0.

- gh-issue-95194: Upgrade bundled pip to 22.2.

- gh-issue-95132: Fix a :mod:`sqlite3` regression where ``*args`` and
``**kwds`` were incorrectly relayed from :py:func:`~sqlite3.connect` to
the :class:`~sqlite3.Connection` factory. The regression was introduced in
3.11a1 with PR 24421 (:gh:`85128`). Patch by Erlend E. Aasland.`

- gh-issue-93157: Fix :mod:`fileinput` module didn't support ``errors``
option when ``inplace`` is true.

- gh-issue-95105: :meth:`wsgiref.types.InputStream.__iter__` should return
``Iterator[bytes]``, not ``Iterable[bytes]``. Patch by Shantanu Jain.

- gh-issue-94857: Fix refleak in ``_io.TextIOWrapper.reconfigure``. Patch by
Kumar Aditya.

- gh-issue-94821: Fix binding of unix socket to empty address on Linux to
use an available address from the abstract namespace, instead of "\0".

- gh-issue-89988: Fix memory leak in :class:`pickle.Pickler` when looking up
:attr:`dispatch_table`. Patch by Kumar Aditya.

- bpo-47025: Drop support for :class:`bytes` on :attr:`sys.path`.

Tests
-----

- gh-issue-95212: Make multiprocessing test case
``test_shared_memory_recreate`` parallel-safe.

Build
-----

- gh-issue-94847: Fixed ``_decimal`` module build issue on GCC when
compiling with LTO and pydebug. Debug builds no longer force inlining of
functions.

- gh-issue-94841: Fix the possible performance regression of
:c:func:`PyObject_Free` compiled with MSVC version 1932.

- gh-issue-94801: ``configure`` now uses custom flags like ``ZLIB_CFLAGS``
and ``ZLIB_LIBS`` when searching for headers and libraries.

- gh-issue-94773: ``deepfreeze.py`` now supports code object with frozensets
that contain incompatible, unsortable types.

Windows
-------

- gh-issue-90844: Allow virtual environments to correctly launch when they
have spaces in the path.

- gh-issue-94772: Fix incorrect handling of shebang lines in py.exe launcher

C API
-----

- gh-issue-92678: Adds unstable C-API functions
``_PyObject_VisitManagedDict`` and ``_PyObject_ClearManagedDict`` to allow
C extensions to allow the VM to manage their object's dictionaries.

- gh-issue-94930: Fix ``SystemError`` raised when
:c:func:`PyArg_ParseTupleAndKeywords` is used with ``#`` in ``(...)`` but
without ``PY_SSIZE_T_CLEAN`` defined.

- gh-issue-94864: Fix ``PyArg_Parse*`` with deprecated format units "u" and
"Z". It returned 1 (success) when warnings are turned into exceptions.

- gh-issue-94731: Python again uses C-style casts for most casting
operations when compiled with C++. This may trigger compiler warnings, if
they are enabled with e.g. ``-Wold-style-cast `` or
``-Wzero-as-null-pointer-constant`` options for ``g++``.

What's New in Python 3.11.0 beta 4?
===================================

*Release date: 2022-07-11*

Security
--------

- gh-issue-87389: :mod:`http.server`: Fix an open redirection vulnerability
in the HTTP server when an URI path starts with ``//``. Vulnerability
discovered, and initial fix proposed, by Hamza Avvan.

- gh-issue-79096: LWPCookieJar and MozillaCookieJar create files with file
mode 600 instead of 644 (Microsoft Windows is not affected)

- gh-issue-92888: Fix ``memoryview`` use after free when accessing the
backing buffer in certain cases.

- gh-issue-68966: The deprecated mailcap module now refuses to inject unsafe
text (filenames, MIME types, parameters) into shell commands. Instead of
using such text, it will warn and act as if a match was not found (or for
test commands, as if the test failed).

Core and Builtins
-----------------

- gh-issue-94694: Fix an issue that could cause code with multi-line method
lookups to have misleading or incorrect column offset information. In some
cases (when compiling a hand-built AST) this could have resulted in a hard
crash of the interpreter.

- gh-issue-93252: Fix an issue that caused internal frames to outlive failed
Python function calls, possibly resulting in memory leaks or hard
interpreter crashes.

- gh-issue-94215: Fix an issue where exceptions raised by line-tracing
events would cause frames to be left in an invalid state, possibly
resulting in a hard crash of the interpreter.

- gh-issue-92228: Disable the compiler's inline-small-exit-blocks
optimization for exit blocks that are associated with source code lines.
This fixes a bug where the debugger cannot tell where an exception handler
ends and the following code block begins.

- gh-issue-94485: Line number of a module's ``RESUME`` instruction is set to
0 as specified in :pep:`626`.

- gh-issue-94438: Account for instructions that can push NULL to the stack
when setting line number in a frame. Prevents some (unlikely) crashes.

- gh-issue-91719: Reload ``opcode`` when raising ``unknown opcode error`` in
the interpreter main loop, for C compilers to generate dispatching code
independently.

- gh-issue-94329: Compile and run code with unpacking of extremely large
sequences (1000s of elements). Such code failed to compile. It now
compiles and runs correctly.

- gh-issue-94360: Fixed a tokenizer crash when reading encoded files with
syntax errors from ``stdin`` with non utf-8 encoded text. Patch by Pablo
Galindo

- gh-issue-88116: Fix an issue when reading line numbers from code objects
if the encoded line numbers are close to ``INT_MIN``. Patch by Pablo
Galindo

- gh-issue-94262: Don't create frame objects for incomplete frames. Prevents
the creation of generators and closures from being observable to Python
and C extensions, restoring the behavior of 3.10 and earlier.

- gh-issue-94192: Fix error for dictionary literals with invalid expression
as value.

- gh-issue-93883: Revise the display strategy of traceback enhanced error
locations. The indicators are only shown when the location doesn't span
the whole line.

- gh-issue-94021: Fix unreachable code warning in ``Python/specialize.c``.

- gh-issue-93516: Store offset of first traceable instruction in code object
to avoid having to recompute it for each instruction when tracing.

- gh-issue-93516: Lazily create a table mapping bytecode offsets to line
numbers to speed up calculation of line numbers when tracing.

- gh-issue-89828: :class:`types.GenericAlias` no longer relays the
``__class__`` attribute. For example, ``isinstance(list[int], type)`` no
longer returns ``True``.

- gh-issue-93671: Fix some exponential backtrace case happening with deeply
nested sequence patterns in match statements. Patch by Pablo Galindo

- gh-issue-93662: Make sure that the end column offsets are correct in
multi-line method calls. Previously, the end column could precede the
column offset.

- gh-issue-93461: :func:`importlib.invalidate_caches` now drops entries from
:data:`sys.path_importer_cache` with a relative path as name. This solves
a caching issue when a process changes its current working directory.

``FileFinder`` no longer inserts a dot in the path, e.g. ``/egg/./spam``
is now ``/egg/spam``.

- gh-issue-93418: Fixed an assert where an f-string has an equal sign '='
following an expression, but there's no trailing brace. For example,
f"{i=".

- gh-issue-93382: Cache the result of :c:func:`PyCode_GetCode` function to
restore the O(1) lookup of the :attr:`~types.CodeType.co_code` attribute.

- gh-issue-93354: Use exponential backoff for specialization counters in the
interpreter. Can reduce the number of failed specializations significantly
and avoid slowdown for those parts of a program that are not suitable for
specialization.

- gh-issue-93021: Fix the :attr:`__text_signature__` for :meth:`__get__`
methods implemented in C. Patch by Jelle Zijlstra.

- gh-issue-92930: Fixed a crash in ``_pickle.c`` from mutating collections
during ``__reduce__`` or ``persistent_id``.

- gh-issue-92914: Always round the allocated size for lists up to the
nearest even number.

- gh-issue-92858: Improve error message for some suites with syntax error
before ':'

- bpo-46142: Make ``--help`` output shorter by moving some info to the new
``--help-env`` and ``--help-xoptions`` command-line options. Also add
``--help-all`` option to print complete usage.

Library
-------

- gh-issue-94736: Fix crash when deallocating an instance of a subclass of
``_multiprocessing.SemLock``. Patch by Kumar Aditya.

- gh-issue-94637: :meth:`SSLContext.set_default_verify_paths` now releases
the GIL around ``SSL_CTX_set_default_verify_paths`` call. The function
call performs I/O and CPU intensive work.

- gh-issue-94607: Fix subclassing complex generics with type variables in
:mod:`typing`. Previously an error message saying ``Some type variables
... are not listed in Generic[...]`` was shown. :mod:`typing` no longer
populates ``__parameters__`` with the ``__parameters__`` of a Python
class.

- gh-issue-93910: The ability to access the other values of an enum on an
enum (e.g. ``Color.RED.BLUE``) has been restored in order to fix a
performance regression.

- gh-issue-93896: Fix :func:`asyncio.run` and
:class:`unittest.IsolatedAsyncioTestCase` to always the set event loop as
it was done in Python 3.10 and earlier. Patch by Kumar Aditya.

- gh-issue-94510: Re-entrant calls to :func:`sys.setprofile` and
:func:`sys.settrace` now raise :exc:`RuntimeError`. Patch by Pablo
Galindo.

- gh-issue-92336: Fix bug where :meth:`linecache.getline` fails on bad files
with :exc:`UnicodeDecodeError` or :exc:`SyntaxError`. It now returns an
empty string as per the documentation.

- gh-issue-94398: Once a :class:`asyncio.TaskGroup` has started shutting
down (i.e., at least one task has failed and the task group has started
cancelling the remaining tasks), it should not be possible to add new
tasks to the task group.

- gh-issue-94254: Fixed types of :mod:`struct` module to be immutable. Patch
by Kumar Aditya.

- gh-issue-94207: Made :class:`_struct.Struct` GC-tracked in order to fix a
reference leak in the :mod:`_struct` module.

- gh-issue-91742: Fix :mod:`pdb` crash after jump caused by a null pointer
dereference. Patch by Kumar Aditya.

- gh-issue-94101: Manual instantiation of :class:`ssl.SSLSession` objects is
no longer allowed as it lead to misconfigured instances that crashed the
interpreter when attributes where accessed on them.

- gh-issue-84753: :func:`inspect.iscoroutinefunction`,
:func:`inspect.isgeneratorfunction`, and
:func:`inspect.isasyncgenfunction` now properly return ``True`` for
duck-typed function-like objects like instances of
:class:`unittest.mock.AsyncMock`.

This makes :func:`inspect.iscoroutinefunction` consistent with the
behavior of :func:`asyncio.iscoroutinefunction`. Patch by Mehdi ABAAKOUK.

- gh-issue-94028: Fix a regression in the :mod:`sqlite3` where statement
objects were not properly cleared and reset after use in cursor iters. The
regression was introduced by PR 27884 in Python 3.11a1. Patch by Erlend E.
Aasland.

- gh-issue-93820: Pickle :class:`enum.Flag` by name.

- gh-issue-93847: Fix repr of enum of generic aliases.

- gh-issue-91404: Revert the :mod:`re` memory leak when a match is
terminated by a signal or memory allocation failure as the implemented fix
caused a major performance regression.

- gh-issue-83499: Fix double closing of file description in :mod:`tempfile`.

- gh-issue-93820: Fixed a regression when :func:`copy.copy`-ing
:class:`enum.Flag` with multiple flag members.

- gh-issue-79512: Fixed names and ``__module__`` value of :mod:`weakref`
classes :class:`~weakref.ReferenceType`, :class:`~weakref.ProxyType`,
:class:`~weakref.CallableProxyType`. It makes them pickleable.

- gh-issue-91389: Fix an issue where :mod:`dis` utilities could report
missing or incorrect position information in the presence of ``CACHE``
entries.

- gh-issue-93626: Set ``__future__.annotations`` to have a ``None``
mandatoryRelease to indicate that it is currently 'TBD'.

- gh-issue-90473: Emscripten and WASI have no home directory and cannot
provide :pep:`370` user site directory.

- gh-issue-90494: :func:`copy.copy` and :func:`copy.deepcopy` now always
raise a TypeError if ``__reduce__()`` returns a tuple with length 6
instead of silently ignore the 6th item or produce incorrect result.

- gh-issue-90549: Fix a multiprocessing bug where a global named resource
(such as a semaphore) could leak when a child process is spawned (as
opposed to forked).

- gh-issue-93521: Fixed a case where dataclasses would try to add
``__weakref__`` into the ``__slots__`` for a dataclass that specified
``weakref_slot=True`` when it was already defined in one of its bases.
This resulted in a ``TypeError`` upon the new class being created.

- gh-issue-79579: :mod:`sqlite3` now correctly detects DML queries with
leading comments. Patch by Erlend E. Aasland.

- gh-issue-93421: Update :data:`sqlite3.Cursor.rowcount` when a DML
statement has run to completion. This fixes the row count for SQL queries
like ``UPDATE ... RETURNING``. Patch by Erlend E. Aasland.

- gh-issue-91162: Support splitting of unpacked arbitrary-length tuple over
``TypeVar`` and ``TypeVarTuple`` parameters. For example:

* ``A[T, *Ts][*tuple[int, ...]]`` -> ``A[int, *tuple[int, ...]]``
* ``A[*Ts, T][*tuple[int, ...]]`` -> ``A[*tuple[int, ...], int]``

- gh-issue-93353: Fix the :func:`importlib.resources.as_file` context
manager to remove the temporary file if destroyed late during Python
finalization: keep a local reference to the :func:`os.remove` function.
Patch by Victor Stinner.

- gh-issue-83658: Make :class:`multiprocessing.Pool` raise an exception if
``maxtasksperchild`` is not ``None`` or a positive int.

- gh-issue-93156: Accessing the :attr:`pathlib.PurePath.parents` sequence of
an absolute path using negative index values produced incorrect results.

- gh-issue-74696: :func:`shutil.make_archive` no longer temporarily changes
the current working directory during creation of standard ``.zip`` or tar
archives.

- gh-issue-89973: Fix :exc:`re.error` raised in :mod:`fnmatch` if the
pattern contains a character range with upper bound lower than lower bound
(e.g. ``[c-a]``). Now such ranges are interpreted as empty ranges.

- gh-issue-92932: Now :func:`~dis.dis` and :func:`~dis.get_instructions`
handle operand values for instructions prefixed by ``EXTENDED_ARG_QUICK``.
Patch by Sam Gross and Dong-hee Na.

- gh-issue-91577: Move imports in :class:`~multiprocessing.SharedMemory`
methods to module level so that they can be executed late in python
finalization.

- gh-issue-91456: Deprecate current default auto() behavior: In 3.13 the
default will be for for auto() to always return the largest member value
incremented by 1, and to raise if incompatible value types are used.

- bpo-47231: Fixed an issue with inconsistent trailing slashes in tarfile
longname directories.

- bpo-46755: In :class:`QueueHandler`, clear ``stack_info`` from
:class:`LogRecord` to prevent stack trace from being written twice.

- bpo-46197: Fix :mod:`ensurepip` environment isolation for subprocess
running ``pip``.

- bpo-45924: Fix :mod:`asyncio` incorrect traceback when future's exception
is raised multiple times. Patch by Kumar Aditya.

- bpo-34828: :meth:`sqlite3.Connection.iterdump` now handles databases that
use ``AUTOINCREMENT`` in one or more tables.

Documentation
-------------

- gh-issue-94321: Document the :pep:`246` style protocol type
:class:`sqlite3.PrepareProtocol`.

- gh-issue-61162: Clarify :mod:`sqlite3` behavior when
:ref:`sqlite3-connection-context-manager`.

- gh-issue-87260: Align :mod:`sqlite3` argument specs with the actual
implementation.

- gh-issue-86986: The minimum Sphinx version required to build the
documentation is now 3.2.

- gh-issue-88831: Augmented documentation of asyncio.create_task().
Clarified the need to keep strong references to tasks and added a code
snippet detailing how to to this.

- bpo-47161: Document that :class:`pathlib.PurePath` does not collapse
initial double slashes because they denote UNC paths.

Tests
-----

- gh-issue-91330: Added more tests for :mod:`dataclasses` to cover behavior
with data descriptor-based fields.

- gh-issue-94208: ``test_ssl`` is now checking for supported TLS version and
protocols in more tests.

- gh-issue-94315: Tests now check for DAC override capability instead of
relying on :func:`os.geteuid`.

- gh-issue-93951: In test_bdb.StateTestCase.test_skip, avoid including
auxiliary importers.

- gh-issue-93957: Provide nicer error reporting from subprocesses in
test_venv.EnsurePipTest.test_with_pip.

- gh-issue-84461: ``run_tests.py`` now handles cross compiling env vars
correctly and pass ``HOSTRUNNER`` to regression tests.

- gh-issue-93616: ``test_modulefinder`` now creates a temporary directory in
``ModuleFinderTest.setUp()`` instead of module scope.

- gh-issue-93575: Fix issue with test_unicode test_raiseMemError. The test
case now use ``test.support.calcobjsize`` to calculate size of PyUnicode
structs. :func:`sys.getsizeof` may return different size when string has
UTF-8 memory.

- gh-issue-90473: WASI does not have a ``chmod(2)`` syscall.
:func:`os.chmod` is now a dummy function on WASI. Skip all tests that
depend on working :func:`os.chmod`.

- gh-issue-90473: Skip tests on WASI that require symlinks with absolute
paths.

- gh-issue-57539: Increase calendar test coverage for
:meth:`calendar.LocaleTextCalendar.formatweekday`.

- gh-issue-90473: Skip symlink tests on WASI. wasmtime uses ``openat2(2)``
with ``RESOLVE_BENEATH`` flag, which prevents symlinks with absolute
paths.

- gh-issue-89858: Fix ``test_embed`` for out-of-tree builds. Patch by Kumar
Aditya.

- gh-issue-92886: Fixing tests that fail when running with optimizations
(``-O``) in ``test_imaplib.py``.

- gh-issue-92886: Fixing tests that fail when running with optimizations
(``-O``) in ``test_zipimport.py``

- bpo-47016: Create a GitHub Actions workflow for verifying bundled pip and
setuptools. Patch by Illia Volochii and Adam Turner.

Build
-----

- gh-issue-94404: ``makesetup`` now works around an issue with sed on macOS
and uses correct CFLAGS for object files that end up in a shared
extension. Module CFLAGS are used before PY_STDMODULE_CFLAGS to avoid
clashes with system headers.

- gh-issue-93584: Address race condition in ``Makefile`` when installing a
PGO build. All ``test`` and ``install`` targets now depend on ``all``
target.

- gh-issue-93491: ``configure`` now detects and reports :pep:`11` support
tiers.

Windows
-------

- gh-issue-93824: Drag and drop of files onto Python files in Windows
Explorer has been enabled for Windows ARM64.

- bpo-42658: Support native Windows case-insensitive path comparisons by
using ``LCMapStringEx`` instead of :func:`str.lower` in
:func:`ntpath.normcase`. Add ``LCMapStringEx`` to the :mod:`_winapi`
module.

Tools/Demos
-----------

- gh-issue-94538: Fix Argument Clinic output to custom file destinations.
Patch by Erlend E. Aasland.

- gh-issue-94430: Allow parameters named ``module`` and ``self`` with custom
C names in Argument Clinic. Patch by Erlend E. Aasland

C API
-----

- gh-issue-93937: The following frame functions and type are now directly
available with ``#include <Python.h>``, it's no longer needed to add
``#include <frameobject.h>``:

* :c:func:`PyFrame_Check`
* :c:func:`PyFrame_GetBack`
* :c:func:`PyFrame_GetBuiltins`
* :c:func:`PyFrame_GetGenerator`
* :c:func:`PyFrame_GetGlobals`
* :c:func:`PyFrame_GetLasti`
* :c:func:`PyFrame_GetLocals`
* :c:type:`PyFrame_Type`

Patch by Victor Stinner.

- gh-issue-91321: Fix the compatibility of the Python C API with C++ older
than C++11. Patch by Victor Stinner.

- gh-issue-91731: Avoid defining the ``static_assert`` when compiling with
C++ 11, where this is a keyword and redefining it can lead to undefined
behavior. Patch by Pablo Galindo

- gh-issue-93442: Add C++ overloads for _Py_CAST_impl() to handle 0/NULL.
This will allow C++ extensions that pass 0 or NULL to macros using
_Py_CAST() to continue to compile.

What's New in Python 3.11.0 beta 3?
===================================

*Release date: 2022-06-01*

Core and Builtins
-----------------

- gh-issue-93359: Ensure that custom :mod:`ast` nodes without explicit end
positions can be compiled. Patch by Pablo Galindo.

- gh-issue-93345: Fix a crash in substitution of a ``TypeVar`` in nested
generic alias after ``TypeVarTuple``.

Build
-----

- gh-issue-69093: Fix ``Modules/Setup.stdlib.in`` rule for ``_sqlite3``
extension.

What's New in Python 3.11.0 beta 2?
===================================

*Release date: 2022-05-30*

Core and Builtins
-----------------

- gh-issue-84694: The ``--experimental-isolated-subinterpreters`` configure
option and ``EXPERIMENTAL_ISOLATED_SUBINTERPRETERS`` macro have been
removed.

- gh-issue-91924: Fix ``__lltrace__`` debug feature if the stdout encoding
is not UTF-8. Patch by Victor Stinner.

- gh-issue-93061: Backward jumps after ``async for`` loops are no longer
given dubious line numbers.

- gh-issue-93065: Fix contextvars HAMT implementation to handle iteration
over deep trees.

The bug was discovered and fixed by Eli Libman. See
`MagicStack/immutables#84
<https://github.com/MagicStack/immutables/issues/84>`_ for more details.

- gh-issue-90473: Decrease default recursion limit on WASI to address
limited call stack size.

- gh-issue-92804: Fix memory leak in ``memoryview`` iterator as it was not
finalized at exit. Patch by Kumar Aditya.

- gh-issue-92236: Remove spurious "LINE" event when starting a generator or
coroutine, visible tracing functions implemented in C.

- gh-issue-92619: Make the compiler duplicate an exit block only if none of
its instructions have a lineno (previously only the first instruction in
the block was checked, leading to unnecessarily duplicated blocks).

- gh-issue-92261: Fix hang when trying to iterate over a ``typing.Union``.

Library
-------

- gh-issue-93297: Make asyncio task groups prevent child tasks from being
GCed

- gh-issue-90817: The :func:`locale.resetlocale` function is deprecated and
will be removed in Python 3.13. Use ``locale.setlocale(locale.LC_ALL,
"")`` instead. Patch by Victor Stinner.

- gh-issue-92728: The :func:`re.template` function and the corresponding
:const:`re.TEMPLATE` and :const:`re.T` flags are restored after they were
removed in 3.11.0b1, but they are now deprecated, so they might be removed
from Python 3.13.

- gh-issue-93044: No longer convert the database argument of
:func:`sqlite3.connect` to bytes before passing it to the factory.

- gh-issue-93010: In a very special case, the email package tried to append
the nonexistent ``InvalidHeaderError`` to the defect list. It should have
been ``InvalidHeaderDefect``.

- gh-issue-92675: Fix :func:`venv.ensure_directories` to accept
:class:`pathlib.Path` arguments in addition to :class:`str` paths. Patch
by David Foster.

- gh-issue-87901: Removed the ``encoding`` argument from :func:`os.popen`
that was added in 3.11b1.

- gh-issue-91922: Fix function :func:`sqlite.connect` and the
:class:`sqlite.Connection` constructor on non-UTF-8 locales. Also, they
now support bytes paths non-decodable with the current FS encoding.

- gh-issue-92839: Fixed crash resulting from calling bisect.insort() or
bisect.insort_left() with the key argument not equal to None.

- gh-issue-90473: :mod:`subprocess` now fails early on Emscripten and WASI
platforms to work around missing :func:`os.pipe` on WASI.

- gh-issue-92671: Fixed :func:`ast.unparse` for empty tuples in the
assignment target context.

- gh-issue-91581: :meth:`~datetime.datetime.utcfromtimestamp` no longer
attempts to resolve ``fold`` in the pure Python implementation, since the
fold is never 1 in UTC. In addition to being slightly faster in the common
case, this also prevents some errors when the timestamp is close to
:attr:`datetime.min <datetime.datetime.min>`. Patch by Paul Ganssle.

- gh-issue-92550: Fix :meth:`pathlib.Path.rglob` for empty pattern.

- gh-issue-92530: Fix an issue that occurred after interrupting
:func:`threading.Condition.notify`.

- gh-issue-92531: The statistics.median_grouped() function now always return
a float. Formerly, it did not convert the input type when for sequences of
length one.

- gh-issue-91810: :class:`~xml.etree.ElementTree.ElementTree` method
:meth:`~xml.etree.ElementTree.ElementTree.write` and function
:func:`~xml.etree.ElementTree.tostring` now use the text file's encoding
("UTF-8" if not available) instead of locale encoding in XML declaration
when ``encoding="unicode"`` is specified.

- gh-issue-90622: Worker processes for
:class:`concurrent.futures.ProcessPoolExecutor` are no longer spawned on
demand (a feature added in 3.9) when the multiprocessing context start
method is ``"fork"`` as that can lead to deadlocks in the child processes
due to a fork happening while threads are running.

- gh-issue-91581: Remove an unhandled error case in the C implementation of
calls to :meth:`datetime.fromtimestamp <datetime.datetime.fromtimestamp>`
with no time zone (i.e. getting a local time from an epoch timestamp).
This should have no user-facing effect other than giving a possibly more
accurate error message when called with timestamps that fall on
10000-01-01 in the local time. Patch by Paul Ganssle.

- bpo-39064: :class:`zipfile.ZipFile` now raises :exc:`zipfile.BadZipFile`
instead of ``ValueError`` when reading a corrupt zip file in which the
central directory offset is negative.

- bpo-45393: Fix the formatting for ``await x`` and ``not x`` in the
operator precedence table when using the :func:`help` system.

- bpo-28249: Set :attr:`doctest.DocTest.lineno` to ``None`` when object does
not have :attr:`__doc__`.

- bpo-45046: Add support of context managers in :mod:`unittest`: methods
:meth:`~unittest.TestCase.enterContext` and
:meth:`~unittest.TestCase.enterClassContext` of class
:class:`~unittest.TestCase`, method
:meth:`~unittest.IsolatedAsyncioTestCase.enterAsyncContext` of class
:class:`~unittest.IsolatedAsyncioTestCase` and function
:func:`unittest.enterModuleContext`.

- bpo-42627: Fix incorrect parsing of Windows registry proxy settings

Documentation
-------------

- gh-issue-86438: Clarify that :option:`-W` and :envvar:`PYTHONWARNINGS` are
matched literally and case-insensitively, rather than as regular
expressions, in :mod:`warnings`.

- gh-issue-92240: Added release dates for "What's New in Python 3.X" for
3.0, 3.1, 3.2, 3.8 and 3.10

- bpo-40838: Document that :func:`inspect.getdoc`,
:func:`inspect.getmodule`, and :func:`inspect.getsourcefile` might return
``None``.

- bpo-38056: Overhaul the :ref:`error-handlers` documentation in
:mod:`codecs`.

- bpo-13553: Document tkinter.Tk args.

Tests
-----

- gh-issue-92670: Skip
``test_shutil.TestCopy.test_copyfile_nonexistent_dir`` test on AIX as the
test uses a trailing slash to force the OS consider the path as a
directory, but on AIX the trailing slash has no effect and is considered
as a file.

Build
-----

- gh-issue-90473: Disable pymalloc and increase stack size on
``wasm32-wasi``.

- bpo-34449: Drop invalid compiler switch ``-fPIC`` for HP aCC on HP-UX.
Patch by Michael Osipov.

Windows
-------

- gh-issue-92817: Ensures that :file:`py.exe` will prefer an active virtual
environment over default tags specified with environment variables or
through a :file:`py.ini` file.

- gh-issue-92984: Explicitly disable incremental linking for non-Debug
builds

- gh-issue-92841: :mod:`asyncio` no longer throws ``RuntimeError: Event loop
is closed`` on interpreter exit after asynchronous socket activity. Patch
by Oleg Iarygin.

- bpo-46907: Update Windows installer to use SQLite 3.38.4.

C API
-----

- gh-issue-92898: Fix C++ compiler warnings when casting function arguments
to ``PyObject*``. Patch by Serge Guelton.

- gh-issue-92913: Ensures changes to
:c:member:`PyConfig.module_search_paths` are ignored unless
:c:member:`PyConfig.module_search_paths_set` is set

- gh-issue-92781: Avoid mixing declarations and code in the C API to fix the
compiler warning: "ISO C90 forbids mixed declarations and code"
[-Werror=declaration-after-statement]. Patch by Victor Stinner.

What's New in Python 3.11.0 beta 1?
===================================

*Release date: 2022-05-06*

Security
--------

- gh-issue-57684: Add the :option:`-P` command line option and the
:envvar:`PYTHONSAFEPATH` environment variable to not prepend a potentially
unsafe path to :data:`sys.path`. Patch by Victor Stinner.

Core and Builtins
-----------------

- gh-issue-89519: Chaining classmethod descriptors (introduced in bpo-19072)
is deprecated. It can no longer be used to wrap other descriptors such as
property(). The core design of this feature was flawed, and it caused a
number of downstream problems.

- gh-issue-92345: ``pymain_run_python()`` now imports ``readline`` and
``rlcompleter`` before sys.path is extended to include the current working
directory of an interactive interpreter. Non-interactive interpreters are
not affected.

- bpo-43857: Improve the :exc:`AttributeError` message when deleting a
missing attribute. Patch by Géry Ogam.

- gh-issue-92245: Make sure that PEP 523 is respected in all cases. In
3.11a7, specialization may have prevented Python-to-Python calls
respecting PEP 523.

- gh-issue-92203: Add a closure keyword-only parameter to exec(). It can
only be specified when exec-ing a code object that uses free variables.
When specified, it must be a tuple, with exactly the number of cell
variables referenced by the code object. closure has a default value of
None, and it must be None if the code object doesn't refer to any free
variables.

- gh-issue-91173: Disable frozen modules in debug builds. Patch by Kumar
Aditya.

- gh-issue-92114: Improve error message when subscript a type with
``__class_getitem__`` set to ``None``.

- gh-issue-92112: Fix crash triggered by an evil custom ``mro()`` on a
metaclass.

- gh-issue-92063: The ``PRECALL_METHOD_DESCRIPTOR_FAST_WITH_KEYWORDS``
instruction now ensures methods are called only on objects of the correct
type.

- gh-issue-92031: Deoptimize statically allocated code objects during
``Py_FINALIZE()`` so that future ``_PyCode_Quicken`` calls always start
with unquickened code.

- gh-issue-92036: Fix a crash in subinterpreters related to the garbage
collector. When a subinterpreter is deleted, untrack all objects tracked
by its GC. To prevent a crash in deallocator functions expecting objects
to be tracked by the GC, leak a strong reference to these objects on
purpose, so they are never deleted and their deallocator functions are not
called. Patch by Victor Stinner.

- gh-issue-92032: The interpreter can now autocomplete soft keywords, as of
now ``match``, ``case``, and ``_`` (wildcard pattern) from :pep:`634`.

- gh-issue-87999: The warning emitted by the Python parser for a numeric
literal immediately followed by keyword has been changed from deprecation
warning to syntax warning.

- gh-issue-91869: Fix an issue where specialized opcodes with extended
arguments could produce incorrect tracing output or lead to assertion
failures.

- gh-issue-91603: Speed up :class:`types.UnionType` instantiation. Based on
patch provided by Yurii Karabas.

- gh-issue-89373: If Python is built in debug mode, Python now ensures that
deallocator functions leave the current exception unchanged. Patch by
Victor Stinner.

- gh-issue-91632: Fix a minor memory leak at exit: release the memory of the
:class:`generic_alias_iterator` type. Patch by Dong-hee Na.

- gh-issue-81548: Octal escapes with value larger than ``0o377`` now produce
a :exc:`DeprecationWarning`. In a future Python version they will be a
:exc:`SyntaxWarning` and eventually a :exc:`SyntaxError`.

- bpo-43950: Use a single compact table for line starts, ends and column
offsets. Reduces memory consumption for location info by half

- gh-issue-91102: Use Argument Clinic for :class:`EncodingMap`. Patch by
Oleg Iarygin.

- gh-issue-91636: Fixed a crash in a garbage-collection edge-case, in which
a ``PyFunction_Type.tp_clear`` function could leave a python function
object in an inconsistent state.

- gh-issue-91603: Speed up :func:`isinstance` and :func:`issubclass` checks
for :class:`types.UnionType`. Patch by Yurii Karabas.

- gh-issue-91625: Fixed a bug in which adaptive opcodes ignored any
preceding ``EXTENDED_ARG``\ s on specialization failure.

- gh-issue-78607: The LLTRACE special build now looks for the name
``__lltrace__`` defined in module globals, rather than the name
``__ltrace__``, which had been introduced as a typo.

- gh-issue-91576: Speed up iteration of ascii strings by 50%. Patch by Kumar
Aditya.

- gh-issue-89279: Improve interpreter performance on Windows by inlining a
few specific macros.

- gh-issue-91502: Add a new :c:func:`_PyFrame_IsEntryFrame` API function, to
check if a :c:type:`PyFrameObject` is an entry frame. Patch by Pablo
Galindo.

- gh-issue-91266: Refactor the ``bytearray`` strip methods ``strip``,
``lstrip`` and ``rstrip`` to use a common implementation.

- gh-issue-91479: Replaced the ``__note__`` field of :exc:`BaseException`
(added in an earlier version of 3.11) with the final design of :pep:`678`.
Namely, :exc:`BaseException` gets an :meth:`add_note` method, and its
``__notes__`` field is created when necessary.

- gh-issue-46055: Speed up right shift of negative integers, by removing
unnecessary creation of temporaries. Original patch by Xinhang Xu,
reworked by Mark Dickinson.

- gh-issue-91462: Make the interpreter's low-level tracing (lltrace) feature
output more readable by displaying opcode names (rather than just
numbers), and by displaying stack contents before each opcode.

- gh-issue-89455: Fixed an uninitialized bool value in the traceback
printing code path that was introduced by the initial bpo-45292 exception
groups work.

- gh-issue-91421: Fix a potential integer overflow in _Py_DecodeUTF8Ex.

- gh-issue-91428: Add ``static const char *const _PyOpcode_OpName[256] =
{...};`` to ``opcode.h`` for debug builds to assist in debugging the
Python interpreter. It is now more convenient to make various forms of
debugging output more human-readable by including opcode names rather than
just the corresponding decimal digits.

- bpo-47120: Make :opcode:`POP_JUMP_IF_TRUE`, :opcode:`POP_JUMP_IF_FALSE`,
:opcode:`POP_JUMP_IF_NONE` and :opcode:`POP_JUMP_IF_NOT_NONE` virtual,
mapping to new relative jump opcodes.

- bpo-45317: Add internal documentation explaining design of new (for 3.11)
frame stack.

- bpo-47197: ctypes used to mishandle ``void`` return types, so that for
instance a function declared like ``ctypes.CFUNCTYPE(None, ctypes.c_int)``
would be called with signature ``int f(int)`` instead of ``void f(int)``.
Wasm targets require function pointers to be called with the correct
signatures so this led to crashes. The problem is now fixed.

- bpo-47120: Make opcodes :opcode:`JUMP_IF_TRUE_OR_POP` and
:opcode:`JUMP_IF_FALSE_OR_POP` relative rather than absolute.

- bpo-47177: Replace the ``f_lasti`` member of the internal
``_PyInterpreterFrame`` structure with a ``prev_instr`` pointer, which
reduces overhead in the main interpreter loop. The ``f_lasti`` attribute
of Python-layer frame objects is preserved for backward-compatibility.

- bpo-46961: Integer mod/remainder operations, including the three-argument
form of :func:`pow`, now consistently return ints from the global small
integer cache when applicable.

- bpo-46962: Classes and functions that unconditionally declared their
docstrings ignoring the `--without-doc-strings` compilation flag no longer
do so.

The classes affected are :class:`ctypes.UnionType`,
:class:`pickle.PickleBuffer`, :class:`testcapi.RecursingInfinitelyError`,
and :class:`types.GenericAlias`.

The functions affected are 24 methods in :mod:`ctypes`.

Patch by Oleg Iarygin.

- bpo-46942: Use Argument Clinic for the :class:`types.MethodType`
constructor. Patch by Oleg Iarygin.

- bpo-46764: Fix wrapping bound methods with @classmethod

- bpo-43464: Optimize :meth:`set.intersection` for non-set arguments.

- bpo-46721: Optimize :meth:`set.issuperset` for non-set argument.

- bpo-46509: Add type-specialized versions of the ``Py_DECREF()``, and use
them for ``float``, ``int``, ``str``, ``bool``, and ``None`` to avoid
pointer-chasing at runtime where types are known at C compile time.

- bpo-46045: Do not use POSIX semaphores on NetBSD

- bpo-36819: Fix crashes in built-in encoders with error handlers that
return position less or equal than the starting position of non-encodable
characters.

- bpo-34093: ``marshal.dumps()`` uses ``FLAG_REF`` for all interned strings.
This makes output more deterministic and helps reproducible build.

- bpo-26579: Added ``object.__getstate__`` which provides the default
implementation of the ``__getstate__()`` method.

Copying and pickling instances of subclasses of builtin types bytearray,
set, frozenset, collections.OrderedDict, collections.deque,
weakref.WeakSet, and datetime.tzinfo now copies and pickles instance
attributes implemented as slots.

Library
-------

- gh-issue-87901: Add the *encoding* parameter to :func:`os.popen`.

- gh-issue-90997: Fix an issue where :mod:`dis` utilities may interpret
populated inline cache entries as valid instructions.

- gh-issue-92332: Deprecate :class:`typing.Text` (removal of the class is
currently not planned). Patch by Alex Waygood.

- Deprecate nested classes in enum definitions becoming members -- in 3.13
they will be normal classes; add `member` and `nonmember` functions to
allow control over results now.

- gh-issue-92356: Fixed a performance regression in ctypes function calls.

- gh-issue-90997: Show the actual named values stored in inline caches when
``show_caches=True`` is passed to :mod:`dis` utilities.

- gh-issue-92301: Prefer ``close_range()`` to iterating over procfs for file
descriptor closing in :mod:`subprocess` for better performance.

- gh-issue-67248: Sort the miscellaneous topics in Cmd.do_help()

- gh-issue-92210: Port ``socket.__init__`` to Argument Clinic. Patch by
Cinder.

- gh-issue-80010: Add support for generalized ISO 8601 parsing to
:meth:`datetime.datetime.fromisoformat`,
:meth:`datetime.date.fromisoformat` and
:meth:`datetime.time.fromisoformat`. Patch by Paul Ganssle.

- gh-issue-92118: Fix a 3.11 regression in
:func:`~contextlib.contextmanager`, which caused it to propagate
exceptions with incorrect tracebacks.

- gh-issue-90887: Adding ``COPYFILE_STAT``, ``COPYFILE_ACL`` and
``COPYFILE_XATTR`` constants for :func:`os.fcopyfile` available in macOs.

- gh-issue-91215: For @dataclass, add weakref_slot. Default is False. If
True, and if slots=True, add a slot named "__weakref__", which will allow
instances to be weakref'd. Contributed by Eric V. Smith

- gh-issue-85984: New function os.login_tty() for Unix.

- gh-issue-92128: Add :meth:`~object.__class_getitem__` to
:class:`logging.LoggerAdapter` and :class:`logging.StreamHandler`,
allowing them to be parameterized at runtime. Patch by Alex Waygood.

- gh-issue-92049: Forbid pickling constants ``re._constants.SUCCESS`` etc.
Previously, pickling did not fail, but the result could not be unpickled.

- gh-issue-92062: :class:`inspect.Parameter` now raises :exc:`ValueError` if
``name`` is a keyword, in addition to the existing check that it is an
identifier.

- gh-issue-87390: Add an ``__unpacked__`` attribute to
:class:`types.GenericAlias`. Patch by Jelle Zijlstra.

- gh-issue-88089: Add support for generic :class:`typing.NamedTuple`.

- gh-issue-91996: New http.HTTPMethod enum to represent all the available
HTTP request methods in a convenient way

- gh-issue-91984: Modified test strings in test_argparse.py to not contain
trailing spaces before end of line.

- gh-issue-91952: Add ``encoding="locale"`` support to
:meth:`TextIOWrapper.reconfigure`.

- gh-issue-91954: Add *encoding* and *errors* arguments to
:func:`subprocess.getoutput` and :func:`subprocess.getstatusoutput`.

- bpo-47029: Always close the read end of the pipe used by
:class:`multiprocessing.Queue` *after* the last write of buffered data to
the write end of the pipe to avoid :exc:`BrokenPipeError` at garbage
collection and at :meth:`multiprocessing.Queue.close` calls. Patch by Géry
Ogam.

- gh-issue-91928: Add `datetime.UTC` alias for `datetime.timezone.utc`.

Patch by Kabir Kwatra.

- gh-issue-68966: The :mod:`mailcap` module is now deprecated and will be
removed in Python 3.13. See :pep:`594` for the rationale and the
:mod:`mimetypes` module for an alternative. Patch by Victor Stinner.

- gh-issue-91401: Provide a way to disable :mod:`subprocess` use of
``vfork()`` just in case it is ever needed and document the existing
mechanism for ``posix_spawn()``.

- gh-issue-64783: Fix :data:`signal.NSIG` value on FreeBSD to accept signal
numbers greater than 32, like :data:`signal.SIGRTMIN` and
:data:`signal.SIGRTMAX`. Patch by Victor Stinner.

- gh-issue-91910: Add missing f prefix to f-strings in error messages from
the :mod:`multiprocessing` and :mod:`asyncio` modules.

- gh-issue-91860: Add :func:`typing.dataclass_transform`, implementing
:pep:`681`. Patch by Jelle Zijlstra.

- gh-issue-91832: Add ``required`` attribute to :class:`argparse.Action`
repr output.

- gh-issue-91827: In the :mod:`tkinter` module add method
``info_patchlevel()`` which returns the exact version of the Tcl library
as a named tuple similar to :data:`sys.version_info`.

- gh-issue-84461: Add :option:`--enable-wasm-pthreads` to enable pthreads
support for WASM builds. ``Emscripten/node`` no longer has threading
enabled by default. Include additional file systems.

- gh-issue-91821: Fix unstable ``test_from_tuple`` test in
``test_decimal.py``.

- gh-issue-91217: Deprecate the xdrlib module.

- gh-issue-91217: Deprecate the uu module.

- gh-issue-91760: More strict rules will be applied for numerical group
references and group names in regular expressions. For now, a deprecation
warning is emitted for group references and group names which will be
errors in future Python versions.

- gh-issue-84461: Add provisional :data:`sys._emscripten_info` named tuple
with build-time and run-time information about Emscripten platform.

- gh-issue-90623: :func:`signal.raise_signal` and :func:`os.kill` now check
immediately for pending signals. Patch by Victor Stinner.

- gh-issue-91734: Fix OSS audio support on Solaris.

- gh-issue-90633: Include the passed value in the exception thrown by
:func:`typing.assert_never`. Patch by Jelle Zijlstra.

- gh-issue-91700: Compilation of regular expression containing a conditional
expression ``(?(group)...)`` now raises an appropriate :exc:`re.error` if
the group number refers to not defined group. Previously an internal
RuntimeError was raised.

- gh-issue-91231: Add an optional keyword *shutdown_timeout* parameter to
the :class:`multiprocessing.BaseManager` constructor. Kill the process if
terminate() takes longer than the timeout. Patch by Victor Stinner.

- gh-issue-91621: Fix :func:`typing.get_type_hints` for
:class:`collections.abc.Callable`. Patch by Shantanu Jain.

- gh-issue-90568: Parsing ``\N`` escapes of Unicode Named Character
Sequences in a :mod:`regular expression <re>` raises now :exc:`re.error`
instead of ``TypeError``.

- gh-issue-91670: Remove deprecated ``SO`` config variable in
:mod:`sysconfig`.

- gh-issue-91217: Deprecate the telnetlib module.

- gh-issue-91217: Deprecate the sunau module.

- gh-issue-91217: Deprecate the spwd module.

- gh-issue-91217: Deprecate the sndhdr module, as well as inline needed
functionality for ``email.mime.MIMEAudio``.

- gh-issue-91616: :mod:`re` module, fix :meth:`~re.Pattern.fullmatch`
mismatch when using Atomic Grouping or Possessive Quantifiers.

- gh-issue-91217: Deprecate the 'pipes' module.

- gh-issue-91217: Deprecate the ossaudiodev module.

- bpo-47256: :mod:`re` module, limit the maximum capturing group to
1,073,741,823 in 64-bit build, this increases the depth of backtracking.

- gh-issue-91217: Deprecate the nis module.

- gh-issue-91595: Fix the comparison of character and integer inside
:func:`Tools.gdb.libpython.write_repr`. Patch by Yu Liu.

- gh-issue-74166: Add option to raise all errors from
:meth:`~socket.create_connection` in an :exc:`ExceptionGroup` when it
fails to create a connection. The default remains to raise only the last
error that had occurred when multiple addresses were tried.

- gh-issue-91487: Optimize asyncio UDP speed, over 100 times faster when
transferring a large file.

- gh-issue-91575: Update case-insensitive matching in the :mod:`re` module
to the latest Unicode version.

- gh-issue-90622: In ``concurrent.futures.process.ProcessPoolExecutor``
disallow the "fork" multiprocessing start method when the new
``max_tasks_per_child`` feature is used as the mix of threads+fork can
hang the child processes. Default to using the safe "spawn" start method
in that circumstance if no ``mp_context`` was supplied.

- gh-issue-89022: In :mod:`sqlite3`, ``SQLITE_MISUSE`` result codes are now
mapped to :exc:`~sqlite3.InterfaceError` instead of
:exc:`~sqlite3.ProgrammingError`. Also, more accurate exceptions are
raised when binding parameters fail. Patch by Erlend E. Aasland.

- gh-issue-91526: Stop calling ``os.device_encoding(file.fileno())`` in
:class:`TextIOWrapper`. It was complex, never documented, and didn't work
for most cases. (Patch by Inada Naoki.)

- gh-issue-88116: Change the frame-related functions in the :mod:`inspect`
module to return a regular object (that is backwards compatible with the
old tuple-like interface) that include the extended :pep:`657` position
information (end line number, column and end column). The affected
functions are: :func:`inspect.getframeinfo`,
:func:`inspect.getouterframes`, :func:`inspect.getinnerframes`,
:func:`inspect.stack` and :func:`inspect.trace`. Patch by Pablo Galindo.

- gh-issue-69093: Add indexing and slicing support to :class:`sqlite3.Blob`.
Patch by Aviv Palivoda and Erlend E. Aasland.

- gh-issue-69093: Add :term:`context manager` support to
:class:`sqlite3.Blob`. Patch by Aviv Palivoda and Erlend E. Aasland.

- gh-issue-91217: Deprecate nntplib.

- gh-issue-91217: Deprecate msilib.

- gh-issue-91404: Improve the performance of :mod:`re` matching by using
computed gotos (or "threaded code") on supported platforms and removing
expensive pointer indirections.

- gh-issue-91217: Deprecate the imghdr module.

- gh-issue-91217: Deprecate the crypt module.

- gh-issue-91276: Make space for longer opcodes in :mod:`dis` output.

- bpo-47000: Make :class:`TextIOWrapper` uses locale encoding when
``encoding="locale"`` is specified even in UTF-8 mode.

- gh-issue-91230: :func:`warnings.catch_warnings` now accepts arguments for
:func:`warnings.simplefilter`, providing a more concise way to locally
ignore warnings or convert them to errors.

- gh-issue-91217: Deprecate the chunk module.

- Add the ``TCP_CONNECTION_INFO`` option (available on macOS) to
:mod:`socket`.

- bpo-47260: Fix ``os.closerange()`` potentially being a no-op in a Linux
seccomp sandbox.

- bpo-47087: Implement ``typing.Required`` and ``typing.NotRequired``
(:pep:`655`). Patch by David Foster and Jelle Zijlstra.

- bpo-47061: Deprecate cgi and cgitb.

- bpo-47061: Deprecate audioop.

- bpo-47000: Add :func:`locale.getencoding` to get the current locale
encoding. It is similar to ``locale.getpreferredencoding(False)`` but
ignores the :ref:`Python UTF-8 Mode <utf8-mode>`.

- bpo-42012: Add :mod:`wsgiref.types`, containing WSGI-specific types for
static type checking.

- bpo-47227: Suppress expression chaining for more :mod:`re` parsing errors.

- bpo-47211: Remove undocumented and never working function
``re.template()`` and flag ``re.TEMPLATE``. This was later reverted in
3.11.0b2 and deprecated instead.

- bpo-47135: :meth:`decimal.localcontext` now accepts context attributes via
keyword arguments

- bpo-43323: Fix errors in the :mod:`email` module if the charset itself
contains undecodable/unencodable characters.

- bpo-46841: Disassembly of quickened code.

- bpo-46681: Forward gzip.compress() compresslevel to zlib.

- bpo-45100: Add :func:`typing.get_overloads` and
:func:`typing.clear_overloads`. Patch by Jelle Zijlstra.

- bpo-44807: :class:`typing.Protocol` no longer silently replaces
:meth:`__init__` methods defined on subclasses. Patch by Adrian Garcia
Badaracco.

- bpo-46787: Fix :class:`concurrent.futures.ProcessPoolExecutor` exception
memory leak

- bpo-46720: Add support for path-like objects to
:func:`multiprocessing.set_executable` for Windows to be on a par with
Unix-like systems. Patch by Géry Ogam.

- bpo-46696: Add ``SO_INCOMING_CPU`` constant to :mod:`socket`.

- bpo-46053: Fix OSS audio support on NetBSD.

- bpo-45639: ``image/avif`` and ``image/webp`` were added to
:mod:`mimetypes`.

- bpo-46285: Add command-line option ``-p``/``--protocol`` to module
:mod:`http.server` which specifies the HTTP version to which the server is
conformant (HTTP/1.1 conformant servers can now be run from the
command-line interface of module :mod:`http.server`). Patch by Géry Ogam.

- bpo-44791: Accept ellipsis as the last argument of
:data:`typing.Concatenate`.

- bpo-46547: Remove variables leaking into ``pydoc.Helper`` class namespace.

- bpo-46415: Fix ipaddress.ip_{address,interface,network} raising TypeError
instead of ValueError if given invalid tuple as address parameter.

- bpo-46075: ``CookieJar`` with ``DefaultCookiePolicy`` now can process
cookies from localhost with domain=localhost explicitly specified in
Set-Cookie header.

- bpo-45995: Add a "z" option to the string formatting specification that
coerces negative zero floating-point values to positive zero after
rounding to the format precision. Contributed by John Belmonte.

- bpo-26175: Fully implement the :class:`io.BufferedIOBase` or
:class:`io.TextIOBase` interface for
:class:`tempfile.SpooledTemporaryFile` objects. This lets them work
correctly with higher-level layers (like compression modules). Patch by
Carey Metcalfe.

- bpo-45138: Fix a regression in the :mod:`sqlite3` trace callback where
bound parameters were not expanded in the passed statement string. The
regression was introduced in Python 3.10 by :issue:`40318`. Patch by
Erlend E. Aasland.

- bpo-44863: Allow :class:`~typing.TypedDict` subclasses to also include
:class:`~typing.Generic` as a base class in class based syntax. Thereby
allowing the user to define a generic ``TypedDict``, just like a
user-defined generic but with ``TypedDict`` semantics.

- bpo-44587: Fix BooleanOptionalAction to not automatically add a default
string. If a default string is desired, use a formatter to add it.

- bpo-43827: All positional-or-keyword parameters to ``ABCMeta.__new__`` are
now positional-only to avoid conflicts with keyword arguments to be passed
to :meth:`__init_subclass__`.

- bpo-43218: Prevent creation of a venv whose path contains the PATH
separator. This could affect the usage of the activate script. Patch by
Dustin Rodrigues.

- bpo-38435: Add a ``process_group`` parameter to :class:`subprocess.Popen`
to help move more things off of the unsafe ``preexec_fn`` parameter.

- bpo-42066: Fix cookies getting sorted in :func:`CookieJar.__iter__` which
is an extra behavior and not mentioned in RFC 2965 or Netscape cookie
protocol. Now the cookies in ``CookieJar`` follows the order of the
``Set-Cookie`` header. Patch by Iman Kermani.

- bpo-40617: Add :meth:`~sqlite3.Connection.create_window_function` to
:class:`sqlite3.Connection` for creating aggregate window functions. Patch
by Erlend E. Aasland.

- bpo-40676: Convert :mod:`csv` to use Argument Clinic for
:func:`csv.field_size_limit`, :func:`csv.get_dialect`,
:func:`csv.unregister_dialect` and :func:`csv.list_dialects`.

- bpo-39716: Raise an ArgumentError when the same subparser name is added
twice to an `argparse.ArgumentParser`. This is consistent with the
(default) behavior when the same option string is added twice to an
ArgumentParser.

- bpo-36073: Raise :exc:`~sqlite3.ProgrammingError` instead of segfaulting
on recursive usage of cursors in :mod:`sqlite3` converters. Patch by
Sergey Fedoseev.

- bpo-34975: Adds a ``start_tls()`` method to
:class:`~asyncio.streams.StreamWriter`, which upgrades the connection with
TLS using the given :class:`~ssl.SSLContext`.

- bpo-22276: :class:`~pathlib.Path` methods :meth:`~pathlib.Path.glob` and
:meth:`~pathlib.Path.rglob` return only directories if *pattern* ends with
a pathname components separator (``/`` or :data:`~os.sep`). Patch by
Eisuke Kawashima.

- bpo-24905: Add :meth:`~sqlite3.Connection.blobopen` to
:class:`sqlite3.Connection`. :class:`sqlite3.Blob` allows incremental I/O
operations on blobs. Patch by Aviv Palivoda and Erlend E. Aasland.

Documentation
-------------

- gh-issue-91888: Add a new `gh` role to the documentation to link to GitHub
issues.

- gh-issue-91783: Document security issues concerning the use of the
function :meth:`shutil.unpack_archive`

- gh-issue-91547: Remove "Undocumented modules" page.

- gh-issue-91298: In ``importlib.resources.abc``, refined the documentation
of the Traversable Protocol, applying changes from importlib_resources
5.7.1.

- bpo-44347: Clarify the meaning of *dirs_exist_ok*, a kwarg of
:func:`shutil.copytree`.

- bpo-36329: Remove 'make -C Doc serve' in favour of 'make -C Doc htmlview'

- bpo-47189: Add a What's New in Python 3.11 entry for the Faster CPython
project. Documentation by Ken Jin and Kumar Aditya.

- bpo-38668: Update the introduction to documentation for :mod:`os.path` to
remove warnings that became irrelevant after the implementations of
:pep:`383` and :pep:`529`.

- bpo-47115: The documentation now lists which members of C structs are part
of the :ref:`Limited API/Stable ABI <stable>`.

- bpo-46962: All docstrings in code snippets are now wrapped into
:func:`PyDoc_STR` to follow the guideline of `PEP 7's Documentation
Strings paragraph
<https://www.python.org/dev/peps/pep-0007/#documentation-strings>`_. Patch
by Oleg Iarygin.

- bpo-26792: Improve the docstrings of :func:`runpy.run_module` and
:func:`runpy.run_path`. Original patch by Andrew Brezovsky.

Tests
-----

- gh-issue-92169: Use ``warnings_helper.import_deprecated()`` to import
deprecated modules uniformly in tests. Patch by Hugo van Kemenade.

- gh-issue-84461: When multiprocessing is enabled, libregrtest can now use a
Python executable other than :code:`sys.executable` via the ``--python``
flag.

- gh-issue-91904: Fix initialization of
:envvar:`PYTHONREGRTEST_UNICODE_GUARD` which prevented running regression
tests on non-UTF-8 locale.

- gh-issue-91752: Added @requires_zlib to
test.test_tools.test_freeze.TestFreeze.

- gh-issue-91607: Fix ``test_concurrent_futures`` to test the correct
multiprocessing start method context in several cases where the test logic
mixed this up.

- bpo-40280: Threading tests are now skipped on WASM targets without pthread
support.

- bpo-47109: Test for :mod:`ctypes.macholib.dyld`,
:mod:`ctypes.macholib.dylib`, and :mod:`ctypes.macholib.framework` are
brought from manual pre-:mod:`unittest` times to :mod:`ctypes.test`
location and structure. Patch by Oleg Iarygin.

- bpo-29890: Add tests for :class:`ipaddress.IPv4Interface` and
:class:`ipaddress.IPv6Interface` construction with tuple arguments.
Original patch and tests by louisom.

Build
-----

- gh-issue-89452: gdbm-compat is now preferred over ndbm if both are
available on the system. This allows avoiding the problematic ndbm.h on
macOS.

- gh-issue-91731: Python is now built with ``-std=c11`` compiler option,
rather than ``-std=c99``. Patch by Victor Stinner.

- bpo-47152: Add script and make target for generating ``sre_constants.h``.

- bpo-47103: Windows ``PGInstrument`` builds now copy a required DLL into
the output directory, making it easier to run the profile stage of a PGO
build.

Windows
-------

- bpo-46907: Update Windows installer to use SQLite 3.38.3.

- bpo-47239: Fixed --list and --list-paths output for :ref:`launcher` when
used in an active virtual environment.

- bpo-46907: Update Windows installer to use SQLite 3.38.2.

- bpo-46785: Fix race condition between :func:`os.stat` and unlinking a file
on Windows, by using errors codes returned by ``FindFirstFileW()`` when
appropriate in ``win32_xstat_impl``.

- bpo-40859: Update Windows build to use xz-5.2.5

macOS
-----

- bpo-46907: Update macOS installer to SQLite 3.38.4.

Tools/Demos
-----------

- gh-issue-91583: Fix regression in the code generated by Argument Clinic
for functions with the ``defining_class`` parameter.

- gh-issue-91575: Add script ``Tools/scripts/generate_re_casefix.py`` and
the make target ``regen-re`` for generating additional data for
case-insensitive matching according to the current Unicode version.

- gh-issue-91551: Remove the ancient Pynche color editor. It has moved to
https://gitlab.com/warsaw/pynche

C API
-----

- gh-issue-88279: Deprecate the C functions: :c:func:`PySys_SetArgv`,
:c:func:`PySys_SetArgvEx`, :c:func:`PySys_SetPath`. Patch by Victor
Stinner.

- gh-issue-92154: Added the :c:func:`PyCode_GetCode` function. This function
does the equivalent of the Python code ``getattr(code_object,
'co_code')``.

- gh-issue-92173: Fix the ``closure`` argument to
:c:func:`PyEval_EvalCodeEx`.

- gh-issue-91320: Fix C++ compiler warnings about "old-style cast" (``g++
-Wold-style-cast``) in the Python C API. Use C++ ``reinterpret_cast<>``
and ``static_cast<>`` casts when the Python C API is used in C++. Patch by
Victor Stinner.

- gh-issue-80527: Mark functions as deprecated by :pep:`623`:
:c:func:`PyUnicode_AS_DATA`, :c:func:`PyUnicode_AS_UNICODE`,
:c:func:`PyUnicode_GET_DATA_SIZE`, :c:func:`PyUnicode_GET_SIZE`. Patch by
Victor Stinner.

- gh-issue-91768: :c:func:`Py_REFCNT`, :c:func:`Py_TYPE`, :c:func:`Py_SIZE`
and :c:func:`Py_IS_TYPE` functions argument type is now ``PyObject*``,
rather than ``const PyObject*``. Patch by Victor Stinner.

- gh-issue-91020: Add ``PyBytes_Type.tp_alloc`` to initialize
``PyBytesObject.ob_shash`` for bytes subclasses.

- bpo-40421: Add ``PyFrame_GetLasti`` C-API function to access frame
object's ``f_lasti`` attribute safely from C code.

- bpo-35134: Remove the ``Include/code.h`` header file. C extensions should
only include the main ``<Python.h>`` header file. Patch by Victor Stinner.

- bpo-47169: :c:func:`PyOS_CheckStack` is now exported in the Stable ABI on
Windows.

- bpo-47169: :c:func:`PyThread_get_thread_native_id` is excluded from the
stable ABI on platforms where it doesn't exist (like Solaris).

- bpo-46343: Added :c:func:`PyErr_GetHandledException` and
:c:func:`PyErr_SetHandledException` as simpler alternatives to
:c:func:`PyErr_GetExcInfo` and :c:func:`PyErr_SetExcInfo`.

They are included in the stable ABI.

What's New in Python 3.11.0 alpha 7?
====================================

*Release date: 2022-04-05*

Core and Builtins
-----------------

- bpo-47212: Raise :exc:`IndentationError` instead of :exc:`SyntaxError` for
a bare ``except`` with no following indent. Improve :exc:`SyntaxError`
locations for an un-parenthesized generator used as arguments. Patch by
Matthieu Dartiailh.

- bpo-47186: Replace :opcode:`JUMP_IF_NOT_EG_MATCH` by
:opcode:`CHECK_EG_MATCH` + jump.

- bpo-47176: Emscripten builds cannot handle signals in the usual way due to
platform limitations. Python can now handle signals. To use, set
Module.Py_EmscriptenSignalBuffer to be a single byte SharedArrayBuffer and
set Py_EMSCRIPTEN_SIGNAL_HANDLING to 1. Writing a number into the
SharedArrayBuffer will cause the corresponding signal to be raised into
the Python thread.

- bpo-47186: Replace :opcode:`JUMP_IF_NOT_EXC_MATCH` by
:opcode:`CHECK_EXC_MATCH` + jump.

- bpo-47120: Replace the absolute jump opcode :opcode:`JUMP_NO_INTERRUPT` by
the relative :opcode:`JUMP_BACKWARD_NO_INTERRUPT`.

- bpo-46841: Avoid unnecessary allocations when comparing code objects.

- bpo-47182: Fix a crash when using a named unicode character like
``"\N{digit nine}"`` after the main interpreter has been initialized a
second time.

- bpo-47162: WebAssembly cannot deal with bad function pointer casts
(different count or types of arguments). Python can now use call
trampolines to mitigate the problem. Define :c:macro:`PY_CALL_TRAMPOLINE`
to enable call trampolines.

- bpo-46775: Some Windows system error codes(>= 10000) are now mapped into
the correct errno and may now raise a subclass of :exc:`OSError`. Patch by
Dong-hee Na.

- bpo-47129: Improve error messages in f-string syntax errors concerning
empty expressions.

- bpo-47117: Fix a crash if we fail to decode characters in interactive mode
if the tokenizer buffers are uninitialized. Patch by Pablo Galindo.

- bpo-47127: Speed up calls to c functions with keyword arguments by 25%
with specialization. Patch by Kumar Aditya.

- bpo-47120: Replaced :opcode:`JUMP_ABSOLUTE` by the relative jump
:opcode:`JUMP_BACKWARD`.

- bpo-42197: :c:func:`PyFrame_FastToLocalsWithError` and
:c:func:`PyFrame_LocalsToFast` are no longer called during profiling nor
tracing. C code can access the ``f_locals`` attribute of
:c:type:`PyFrameObject` by calling :c:func:`PyFrame_GetLocals`.

- bpo-47070: Improve performance of ``array_inplace_repeat`` by reducing the
number of invocations of ``memcpy``. Refactor the ``repeat`` and inplace
``repeat`` methods of ``array``, ``bytes``, ``bytearray`` and
``unicodeobject`` to use the common ``_PyBytes_Repeat``.

- bpo-47053: Reduce de-optimization in the specialized
``BINARY_OP_INPLACE_ADD_UNICODE`` opcode.

- bpo-47045: Remove the ``f_state`` field from the _PyInterpreterFrame
struct. Add the ``owner`` field to the _PyInterpreterFrame struct to make
ownership explicit to simplify clearing and deallocing frames and
generators.

- bpo-46968: Check for the existence of the "sys/auxv.h" header in
:mod:`faulthandler` to avoid compilation problems in systems where this
header doesn't exist. Patch by Pablo Galindo

- bpo-46329: Use low bit of ``LOAD_GLOBAL`` to indicate whether to push a
``NULL`` before the global. Helps streamline the call sequence a bit.

- bpo-46841: Quicken bytecode in-place by storing it as part of the
corresponding ``PyCodeObject``.

- bpo-47012: Speed up iteration of :class:`bytes` and :class:`bytearray` by
30%. Patch by Kumar Aditya.

- bpo-47009: Improved the performance of :meth:`list.append()` and list
comprehensions by optimizing for the common case, where no resize is
needed. Patch by Dennis Sweeney.

- bpo-47005: Improve performance of ``bytearray_repeat`` and
``bytearray_irepeat`` by reducing the number of invocations of ``memcpy``.

- bpo-46829: Deprecate passing a message into :meth:`asyncio.Future.cancel`
and :meth:`asyncio.Task.cancel`

- bpo-46993: Speed up :class:`bytearray` creation from :class:`list` and
:class:`tuple` by 40%. Patch by Kumar Aditya.

- bpo-39829: Removed the ``__len__()`` call when initializing a list and
moved initializing to ``list_extend``. Patch by Jeremiah Pascual.

- bpo-46944: Speed up throwing exception in generator with
:const:`METH_FASTCALL` calling convention. Patch by Kumar Aditya.

- bpo-46841: Modify :opcode:`STORE_SUBSCR` to use an inline cache entry
(rather than its oparg) as an adaptive counter.

- bpo-46841: Use inline caching for :opcode:`PRECALL` and :opcode:`CALL`,
and remove the internal machinery for managing the (now unused) non-inline
caches.

- bpo-46881: Statically allocate and initialize the latin1 characters.

- bpo-46838: Improve syntax errors for incorrect function definitions. Patch
by Pablo Galindo

- bpo-43721: Fix docstrings of :attr:`~property.getter`,
:attr:`~property.setter`, and :attr:`~property.deleter` to clarify that
they create a new copy of the property.

- bpo-43224: Make grammar changes required for PEP 646.

Library
-------

- bpo-47208: Allow vendors to override :const:`CTYPES_MAX_ARGCOUNT`.

- bpo-23689: :mod:`re` module: fix memory leak when a match is terminated by
a signal or memory allocation failure. Patch by Ma Lin.

- bpo-47167: Allow overriding a future compliance check in
:class:`asyncio.Task`.

- bpo-47151: When subprocess tries to use vfork, it now falls back to fork
if vfork returns an error. This allows use in situations where vfork isn't
allowed by the OS kernel.

- bpo-47152: Convert the :mod:`re` module into a package. Deprecate modules
``sre_compile``, ``sre_constants`` and ``sre_parse``.

- bpo-4833: Add :meth:`ZipFile.mkdir`

- bpo-27929: Fix :meth:`asyncio.loop.sock_connect` to only resolve names for
:const:`socket.AF_INET` or :const:`socket.AF_INET6` families. Resolution
may not make sense for other families, like :const:`socket.AF_BLUETOOTH`
and :const:`socket.AF_UNIX`.

- bpo-14265: Adds the fully qualified test name to unittest output

- bpo-47061: Deprecate the aifc module.

- bpo-39622: Handle Ctrl+C in asyncio programs to interrupt the main task.

- bpo-47101: :const:`hashlib.algorithms_available` now lists only algorithms
that are provided by activated crypto providers on OpenSSL 3.0. Legacy
algorithms are not listed unless the legacy provider has been loaded into
the default OSSL context.

- bpo-47099: All :exc:`URLError` exception messages raised in
:class:`urllib.request.URLopener` now contain a colon between ``ftp
error`` and the rest of the message. Previously,
:func:`~urllib.request.URLopener.open_ftp` missed the colon. Patch by Oleg
Iarygin.

- bpo-47099: Exception chaining is changed from
:func:`Exception.with_traceback`/:func:`sys.exc_info` to :pep:`3134`.
Patch by Oleg Iarygin.

- bpo-47095: :mod:`hashlib`'s internal ``_blake2`` module now prefers
``libb2`` from https://www.blake2.net/ over Python's vendored copy of
blake2.

- bpo-47098: The Keccak Code Package for :mod:`hashlib`'s internal ``_sha3``
module has been replaced with tiny_sha3. The module is used as fallback
when Python is built without OpenSSL.

- bpo-47088: Implement :data:`typing.LiteralString`, part of :pep:`675`.
Patch by Jelle Zijlstra.

- bpo-42885: Optimize :func:`re.search`, :func:`re.split`,
:func:`re.findall`, :func:`re.finditer` and :func:`re.sub` for regular
expressions starting with ``\A`` or ``^``.

- bpo-23691: Protect the :func:`re.finditer` iterator from re-entering.

- bpo-47067: Optimize calling ``GenericAlias`` objects by using :pep:`590`
``vectorcall`` and by replacing ``PyObject_SetAttrString`` with
``PyObject_SetAttr``.

- bpo-28080: Add the *metadata_encoding* parameter in the
:class:`zipfile.ZipFile` constructor and the ``--metadata-encoding``
option in the :mod:`zipfile` CLI to allow reading zipfiles using
non-standard codecs to encode the filenames within the archive.

- bpo-47000: Make :func:`io.text_encoding` returns "utf-8" when UTF-8 mode
is enabled.

- bpo-42369: Fix thread safety of :meth:`zipfile._SharedFile.tell` to avoid
a "zipfile.BadZipFile: Bad CRC-32 for file" exception when reading a
:class:`ZipFile` from multiple threads.

- bpo-38256: Fix :func:`binascii.crc32` when it is compiled to use zlib'c
crc32 to work properly on inputs 4+GiB in length instead of returning the
wrong result. The workaround prior to this was to always feed the function
data in increments smaller than 4GiB or to just call the zlib module
function.

We also have :func:`binascii.crc32` release the GIL when computing on
larger inputs as :func:`zlib.crc32` and :mod:`hashlib` do.

This also boosts performance on Windows as it now uses the zlib crc32
implementation for :func:`binascii.crc32` for a 2-3x speedup.

That the stdlib has a crc32 API in two modules is a known historical
oddity. This moves us closer to a single implementation behind them.

- bpo-47066: Global inline flags (e.g. ``(?i)``) can now only be used at the
start of the regular expressions. Using them not at the start of
expression was deprecated since Python 3.6.

- bpo-39394: A warning about inline flags not at the start of the regular
expression now contains the position of the flag.

- bpo-433030: Add support of atomic grouping (``(?>...)``) and possessive
quantifiers (``*+``, ``++``, ``?+``, ``{m,n}+``) in :mod:`regular
expressions <re>`.

- bpo-47062: Implement :class:`asyncio.Runner` context manager.

- bpo-46382: :func:`~dataclasses.dataclass` ``slots=True`` now correctly
omits slots already defined in base classes. Patch by Arie Bovenberg.

- bpo-47057: Use FASTCALL convention for ``FutureIter.throw()``

- bpo-47061: Deprecate the various modules listed by :pep:`594`:

aifc, asynchat, asyncore, audioop, cgi, cgitb, chunk, crypt, imghdr,
msilib, nntplib, nis, ossaudiodev, pipes, smtpd, sndhdr, spwd, sunau,
telnetlib, uu, xdrlib

- bpo-34790: Remove passing coroutine objects to :func:`asyncio.wait`.

- bpo-47039: Normalize ``repr()`` of asyncio future and task objects.

- bpo-2604: Fix bug where doctests using globals would fail when run
multiple times.

- bpo-45150: Add :func:`hashlib.file_digest` helper for efficient hashing of
file object.

- bpo-34861: Made cumtime the default sorting key for cProfile

- bpo-45997: Fix :class:`asyncio.Semaphore` re-aquiring FIFO order.

- bpo-47022: The :mod:`asynchat`, :mod:`asyncore` and :mod:`smtpd` modules
have been deprecated since at least Python 3.6. Their documentation and
deprecation warnings and have now been updated to note they will removed
in Python 3.12 (:pep:`594`).

- bpo-43253: Fix a crash when closing transports where the underlying socket
handle is already invalid on the Proactor event loop.

- bpo-40280: :func:`select.select` now passes ``NULL`` to ``select`` for
each empty fdset.

- bpo-47004: Apply bugfixes from importlib_metadata 4.11.3, including bugfix
for EntryPoint.extras, which was returning match objects and not the
extras strings.

- bpo-46998: Allow subclassing of :class:`typing.Any`. Patch by Shantanu
Jain.

- bpo-46995: Deprecate missing :meth:`asyncio.Task.set_name` for third-party
task implementations, schedule making it mandatory in Python 3.13.

- bpo-46994: Accept explicit contextvars.Context in
:func:`asyncio.create_task` and :meth:`asyncio.loop.create_task`.

- bpo-46981: ``typing.get_args(typing.Tuple[()])`` now returns ``()``
instead of ``((),)``.

- bpo-46968: Add ``os.sysconf_names['SC_MINSIGSTKSZ']``.

- bpo-46985: Upgrade pip wheel bundled with ensurepip (pip 22.0.4)

- bpo-46968: :mod:`faulthandler`: On Linux 5.14 and newer, dynamically
determine size of signal handler stack size CPython allocates using
``getauxval(AT_MINSIGSTKSZ)``. This changes allows for Python extension's
request to Linux kernel to use AMX_TILE instruction set on Sapphire Rapids
Xeon processor to succeed, unblocking use of the ISA in frameworks.

- bpo-46917: The :data:`math.nan` value is now always available. Patch by
Victor Stinner.

- bpo-46955: Expose :class:`asyncio.base_events.Server` as
:class:`asyncio.Server`. Patch by Stefan Zabka.

- bpo-23325: The :mod:`signal` module no longer assumes that
:const:`~signal.SIG_IGN` and :const:`~signal.SIG_DFL` are small int
singletons.

- bpo-46932: Update bundled libexpat to 2.4.7

- bpo-46933: The :mod:`pwd` module is now optional.
:func:`os.path.expanduser` returns the path when the :mod:`pwd` module is
not available.

- bpo-40059: :pep:`680`, the :mod:`tomllib` module. Adds support for parsing
TOML.

- bpo-464471: :func:`asyncio.timeout` and :func:`asyncio.timeout_at` context
managers added. Patch by Tin Tvrtković and Andrew Svetlov.

- bpo-46805: Added raw datagram socket functions for asyncio:
:meth:`~asyncio.AbstractEventLoop.sock_sendto`,
:meth:`~asyncio.AbstractEventLoop.sock_recvfrom` and
:meth:`~asyncio.AbstractEventLoop.sock_recvfrom_into`.

- bpo-46644: No longer require valid typeforms to be callable. This allows
:data:`typing.Annotated` to wrap :data:`typing.ParamSpecArgs` and
:data:`dataclasses.InitVar`. Patch by Gregory Beauregard.

- bpo-46581: Brings :class:`ParamSpec` propagation for :class:`GenericAlias`
in line with :class:`Concatenate` (and others).

- bpo-45413: Define *posix_venv* and *nt_venv* :ref:`sysconfig installation
schemes <installation_paths>` to be used for bootstrapping new virtual
environments. Add *venv* sysconfig installation scheme to get the
appropriate one of the above. The schemes are identical to the
pre-existing *posix_prefix* and *nt* install schemes. The :mod:`venv`
module now uses the *venv* scheme to create new virtual environments
instead of hardcoding the paths depending only on the platform. Downstream
Python distributors customizing the *posix_prefix* or *nt* install scheme
in a way that is not compatible with the install scheme used in virtual
environments are encouraged not to customize the *venv* schemes. When
Python itself runs in a virtual environment,
:func:`sysconfig.get_default_scheme` and
:func:`sysconfig.get_preferred_scheme` with ``key="prefix"`` returns
*venv*.

- bpo-43224: Implement support for PEP 646 in typing.py.

- bpo-43224: Allow unpacking types.GenericAlias objects, e.g. ``*tuple[int,
str]``.

- bpo-46557: Warnings captured by the logging module are now logged without
a format string to prevent systems that group logs by the msg argument
from grouping captured warnings together.

- bpo-41370: :func:`typing.get_type_hints` now supports evaluating strings
as forward references in :ref:`PEP 585 generic aliases
<types-genericalias>`.

- bpo-46607: Add :exc:`DeprecationWarning` to :class:`LegacyInterpolation`,
deprecated in the docstring since Python 3.2. Will be removed in Python
3.13. Use :class:`BasicInterpolation` or :class:`ExtendedInterpolation`
instead.

- bpo-26120: :mod:`pydoc` now excludes __future__ imports from the module's
data items.

- bpo-46480: Add :func:`typing.assert_type`. Patch by Jelle Zijlstra.

- bpo-46421: Fix a unittest issue where if the command was invoked as
``python -m unittest`` and the filename(s) began with a dot (.), a
``ValueError`` is returned.

- bpo-46245: Add optional parameter *dir_fd* in :func:`shutil.rmtree`.

- bpo-22859: :meth:`~unittest.TestProgram.usageExit` is marked deprecated,
to be removed in 3.13.

- bpo-46170: Improve the error message when you try to subclass an instance
of :class:`typing.NewType`.

- bpo-40296: Fix supporting generic aliases in :mod:`pydoc`.

- bpo-20392: Fix inconsistency with uppercase file extensions in
:meth:`MimeTypes.guess_type`. Patch by Kumar Aditya.

- bpo-46030: Add ``LOCAL_CREDS``, ``LOCAL_CREDS_PERSISTENT`` and
``SCM_CREDS2`` FreeBSD constants to the socket module.

- bpo-44439: Fix ``.write()`` method of a member file in ``ZipFile``, when
the input data is an object that supports the buffer protocol, the file
length may be wrong.

- bpo-45171: Fix handling of the ``stacklevel`` argument to logging
functions in the :mod:`logging` module so that it is consistent across all
logging functions and, as advertised, similar to the ``stacklevel``
argument used in :meth:`~warnings.warn`.

- bpo-24959: Fix bug where :mod:`unittest` sometimes drops frames from
tracebacks of exceptions raised in tests.

- bpo-44859: Raise more accurate and :pep:`249` compatible exceptions in
:mod:`sqlite3`.

* Raise :exc:`~sqlite3.InterfaceError` instead of
:exc:`~sqlite3.ProgrammingError` for ``SQLITE_MISUSE`` errors.
* Don't overwrite :exc:`BufferError` with :exc:`ValueError` when conversion to
BLOB fails.
* Raise :exc:`~sqlite3.ProgrammingError` instead of :exc:`~sqlite3.Warning` if
user tries to :meth:`~sqlite3.Cursor.execute()` more than one SQL statement.
* Raise :exc:`~sqlite3.ProgrammingError` instead of :exc:`ValueError` if an SQL
query contains null characters.

- bpo-44493: Add missing terminated NUL in sockaddr_un's length

This was potentially observable when using non-abstract AF_UNIX datagram
sockets to processes written in another programming language.

- bpo-41930: Add :meth:`~sqlite3.Connection.serialize` and
:meth:`~sqlite3.Connection.deserialize` support to :mod:`sqlite3`. Patch
by Erlend E. Aasland.

- bpo-33178: Added :class:`ctypes.BigEndianUnion` and
:class:`ctypes.LittleEndianUnion` classes, as originally documented in the
library docs but not yet implemented.

- bpo-43352: Add an Barrier object in synchronization primitives of
*asyncio* Lib in order to be consistant with Barrier from *threading* and
*multiprocessing* libs*

- bpo-35859: :mod:`re` module, fix a few bugs about capturing group. In rare
cases, capturing group gets an incorrect string. Patch by Ma Lin.

Documentation
-------------

- bpo-45099: Document internal :mod:`asyncio` API.

- bpo-47126: Update PEP URLs to :pep:`676`'s new canonical form.

- bpo-47040: Clarified the old Python versions compatiblity note of
:func:`binascii.crc32` / :func:`zlib.adler32` / :func:`zlib.crc32`
functions.

- bpo-46033: Clarify ``for`` statement execution in its doc.

- bpo-45790: Adjust inaccurate phrasing in
:doc:`../extending/newtypes_tutorial` about the ``ob_base`` field and the
macros used to access its contents.

- bpo-42340: Document that in some circumstances :exc:`KeyboardInterrupt`
may cause the code to enter an inconsistent state. Provided a sample
workaround to avoid it if needed.

- bpo-41233: Link the errnos referenced in ``Doc/library/exceptions.rst`` to
their respective section in ``Doc/library/errno.rst``, and vice versa.
Previously this was only done for EINTR and InterruptedError. Patch by Yan
"yyyyyyyan" Orestes.

Tests
-----

- bpo-47205: Skip test for :func:`~os.sched_getaffinity` and
:func:`~os.sched_setaffinity` error case on FreeBSD.

- bpo-46126: Restore 'descriptions' when running tests internally.

- bpo-47104: Rewrite :func:`asyncio.to_thread` tests to use
:class:`unittest.IsolatedAsyncioTestCase`.

- bpo-40280: The test suite is now passing on the Emscripten platform. All
fork, socket, and subprocess-based tests are skipped.

- bpo-47037: Skip ``strftime("%4Y")`` feature test on Windows. It can cause
an assertion error in debug builds.

- bpo-46587: Skip tests if platform's ``strftime`` does not support
non-portable glibc extensions.

- bpo-47015: A test case for :func:`os.sendfile` is converted from
deprecated :mod:`asyncore` (see :pep:`594`) to :mod:`asyncio`. Patch by
Oleg Iarygin.

Build
-----

- bpo-40280: Add configure option :option:`--enable-wasm-dynamic-linking` to
enable ``dlopen`` and MAIN_MODULE / SIDE_MODULE on ``wasm32-emscripten``.

- bpo-46023: ``makesetup`` now detects and skips all duplicated module
definitions. The first entry wins.

- bpo-40280: Add SOABI ``wasm32-emscripten`` for Emscripten and
``wasm32-wasi`` for WASI on 32bit WASM as well as ``wasm64`` counter
parts.

- bpo-47032: Ensure Windows install builds fail correctly with a non-zero
exit code when part of the build fails.

- bpo-47024: Update OpenSSL to 1.1.1n for macOS installers and all Windows
builds.

- bpo-46996: The :mod:`tkinter` package now requires Tcl/Tk version 8.5.12
or newer.

- bpo-46973: Add ``regen-configure`` make target to regenerate configure
script with Christian's container image
``quay.io/tiran/cpython_autoconf:269``.

- bpo-46917: Building Python now requires support of IEEE 754 floating point
numbers. Patch by Victor Stinner.

- bpo-45774: ``configure`` now verifies that all SQLite C APIs needed for
the :mod:`sqlite3` extension module are found.

Windows
-------

- bpo-47194: Update ``zlib`` to v1.2.12 to resolve CVE-2018-25032.

- bpo-47171: Enables installing the :file:`py.exe` launcher on Windows
ARM64.

- bpo-46566: Upgraded :ref:`launcher` to support a new ``-V:company/tag``
argument for full :pep:`514` support and to detect ARM64 installs. The
``-64`` suffix on arguments is deprecated, but still selects any
non-32-bit install. Setting :envvar:`PYLAUNCHER_ALLOW_INSTALL` and
specifying a version that is not installed will attempt to install the
requested version from the Microsoft Store.

- bpo-47086: The installer for Windows now includes documentation as loose
HTML files rather than a single compiled :file:`.chm` file.

- bpo-46907: Update Windows installer to use SQLite 3.38.1.

- bpo-44549: Update bzip2 to 1.0.8 in Windows builds to mitigate
CVE-2016-3189 and CVE-2019-12900

- bpo-46948: Prevent CVE-2022-26488 by ensuring the Add to PATH option in
the Windows installer uses the correct path when being repaired.

macOS
-----

- bpo-46890: Fix a regression in the setting of ``sys._base_executable`` in
framework builds, and thereby fix a regression in :mod:`venv` virtual
environments with such builds.

- bpo-46907: Update macOS installer to SQLite 3.38.1.

Tools/Demos
-----------

- bpo-40280: Replace Emscripten's limited shell with Katie Bell's browser-ui
REPL from python-wasm project.

C API
-----

- bpo-40421: Add ``PyFrame_GetBuiltins``, ``PyFrame_GetGenerator`` and
``PyFrame_GetGlobals`` C-API functions to access frame object attributes
safely from C code.

- bpo-46850: Move the private ``_PyFrameEvalFunction`` type, and private
``_PyInterpreterState_GetEvalFrameFunc()`` and
``_PyInterpreterState_SetEvalFrameFunc()`` functions to the internal C
API. The ``_PyFrameEvalFunction`` callback function type now uses the
``_PyInterpreterFrame`` type which is part of the internal C API. Patch by
Victor Stinner.

- bpo-46850: Move the private undocumented ``_PyEval_EvalFrameDefault()``
function to the internal C API. The function now uses the
``_PyInterpreterFrame`` type which is part of the internal C API. Patch by
Victor Stinner.

- bpo-46850: Remove the private undocumented function
``_PyEval_CallTracing()`` from the C API. Call the public
:func:`sys.call_tracing` function instead. Patch by Victor Stinner.

- bpo-46850: Remove the private undocumented function
``_PyEval_GetCoroutineOriginTrackingDepth()`` from the C API. Call the
public :func:`sys.get_coroutine_origin_tracking_depth` function instead.
Patch by Victor Stinner.

- bpo-46850: Remove the following private undocumented functions from the C
API:

* ``_PyEval_GetAsyncGenFirstiter()``
* ``_PyEval_GetAsyncGenFinalizer()``
* ``_PyEval_SetAsyncGenFirstiter()``
* ``_PyEval_SetAsyncGenFinalizer()``

Call the public :func:`sys.get_asyncgen_hooks` and
:func:`sys.set_asyncgen_hooks` functions instead. Patch by Victor Stinner.

- bpo-46987: Remove private functions ``_PySys_GetObjectId()`` and
``_PySys_SetObjectId()``. Patch by Dong-hee Na.

- bpo-46906: Add new functions to pack and unpack C double (serialize and
deserialize): :c:func:`PyFloat_Pack2`, :c:func:`PyFloat_Pack4`,
:c:func:`PyFloat_Pack8`, :c:func:`PyFloat_Unpack2`,
:c:func:`PyFloat_Unpack4` and :c:func:`PyFloat_Unpack8`. Patch by Victor
Stinner.

What's New in Python 3.11.0 alpha 6?
====================================

*Release date: 2022-03-07*

Core and Builtins
-----------------

- bpo-46940: Avoid overriding :exc:`AttributeError` metadata information for
nested attribute access calls. Patch by Pablo Galindo.

- bpo-46927: Include the type's name in the error message for subscripting
non-generic types.

- bpo-46921: Support vectorcall for ``super()``. Patch by Ken Jin.

- bpo-46841: Fix incorrect handling of inline cache entries when
specializing :opcode:`BINARY_OP`.

- bpo-46841: Use an oparg to simplify the construction of helpful error
messages in :opcode:`GET_AWAITABLE`.

- bpo-46903: Make sure that str subclasses can be used as attribute names
for instances with virtual dictionaries. Fixes regression in 3.11alpha

- bpo-46841: Add more detailed specialization failure stats for
:opcode:`COMPARE_OP` followed by :opcode:`EXTENDED_ARG`.

- bpo-46891: Fix bug introduced during 3.11alpha where subclasses of
``types.ModuleType`` with ``__slots__`` were not initialized correctly,
resulting in an interpreter crash.

- bpo-46841: Use inline caching for :opcode:`LOAD_ATTR`,
:opcode:`LOAD_METHOD`, and :opcode:`STORE_ATTR`.

- bpo-46841: Use inline cache for :opcode:`BINARY_SUBSCR`.

- bpo-46841: Use inline caching for :opcode:`COMPARE_OP`.

- bpo-46864: Deprecate ``PyBytesObject.ob_shash``. It will be removed in
Python 3.13.

- bpo-46841: Use inline caching for :opcode:`UNPACK_SEQUENCE`.

- bpo-46845: Reduces dict size by removing hash value from hash table when
all inserted keys are Unicode. For example,
``sys.getsizeof(dict.fromkeys("abcdefg"))`` becomes 272 bytes from 352
bytes on 64bit platform.

- bpo-46841: Use inline cache for :opcode:`LOAD_GLOBAL`.

- bpo-46852: Rename the private undocumented ``float.__set_format__()``
method to ``float.__setformat__()`` to fix a typo introduced in Python
3.7. The method is only used by test_float. Patch by Victor Stinner.

- bpo-46852: Remove the undocumented private ``float.__set_format__()``
method, previously known as ``float.__setformat__()`` in Python 3.7. Its
docstring said: "You probably don't want to use this function. It exists
mainly to be used in Python's test suite." Patch by Victor Stinner.

- bpo-40116: Fix regression that dict.update(other) may don't respect
iterate order of other when other is key sharing dict.

- bpo-46712: Share global string identifiers in deep-frozen modules.

- bpo-46430: Fix memory leak in interned strings of deep-frozen modules.

- bpo-46841: Store :opcode:`BINARY_OP` caches inline using a new
:opcode:`CACHE` instruction.

- bpo-45107: Specialize ``LOAD_METHOD`` for instances with a dict.

- bpo-44337: Reduce the memory usage of specialized :opcode:`LOAD_ATTR` and
:opcode:`STORE_ATTR` instructions.

- bpo-46729: Add number of sub-exceptions to :meth:`BaseException.__str__`.

- bpo-45885: Don't un-adapt :opcode:`COMPARE_OP` when collecting
specialization stats.

- bpo-46329: Fix specialization stats gathering for :opcode:`PRECALL`
instructions.

- bpo-46794: Bump up the libexpat version into 2.4.6

- bpo-46823: Implement a specialized combined opcode
``LOAD_FAST__LOAD_ATTR_INSTANCE_VALUE``. Patch by Dennis Sweeney.

- bpo-46820: Fix parsing a numeric literal immediately (without spaces)
followed by "not in" keywords, like in ``1not in x``. Now the parser only
emits a warning, not a syntax error.

- bpo-46329: Move ``KW_NAMES`` before ``PRECALL`` instruction in call
sequence. Change ``operand`` of ``CALL`` to match ``PRECALL`` for easier
specialization.

- bpo-46808: Remove the ``NEXT_BLOCK`` macro from compile.c, and make the
compiler automatically generate implicit blocks when they are needed.

- bpo-46329: Add ``PUSH_NULL`` instruction. This is used as a prefix when
evaluating a callable, so that the stack has the same shape for methods
and other calls. ``PRECALL_FUNCTION`` and ``PRECALL_METHOD`` are merged
into a single ``PRECALL`` instruction.

There is no change in semantics.

- bpo-46762: Fix an assert failure in debug builds when a '<', '>', or '='
is the last character in an f-string that's missing a closing right brace.

- bpo-46730: Message of AttributeError caused by getting, setting or
deleting a property without the corresponding function now mentions that
the attribute is in fact a property and also specifies type of the class
that it belongs to.

- bpo-46724: Make sure that all backwards jumps use the ``JUMP_ABSOLUTE``
instruction, rather than ``JUMP_FORWARD`` with an argument of
``(2**32)+offset``.

- bpo-46732: Correct the docstring for the :meth:`__bool__` method. Patch by
Jelle Zijlstra.

- bpo-46072: Add more detailed specialization failure statistics for
:opcode:`BINARY_OP`.

- bpo-46707: Avoid potential exponential backtracking when producing some
syntax errors involving lots of brackets. Patch by Pablo Galindo.

- bpo-46323: :mod:`ctypes` now allocates memory on the stack instead of on
the heap to pass arguments while calling a Python callback function. Patch
by Dong-hee Na.

- bpo-45923: Add a quickened form of :opcode:`RESUME` that skips quickening
checks.

- bpo-46702: Specialize :opcode:`UNPACK_SEQUENCE` for :class:`tuple` and
:class:`list` unpackings.

- bpo-46072: Opcode pair stats are now gathered with ``--enable-pystats``.
Defining ``DYNAMIC_EXECUTION_PROFILE`` or ``DXPAIRS`` no longer has any
effect.

- bpo-46675: Allow more than 16 items in a split dict before it is combined.
The limit is now 254.

- bpo-40479: Add a missing call to ``va_end()`` in
``Modules/_hashopenssl.c``.

- bpo-46323: Use :c:func:`PyObject_Vectorcall` while calling ctypes callback
function. Patch by Dong-hee Na.

- bpo-46615: When iterating over sets internally in ``setobject.c``, acquire
strong references to the resulting items from the set. This prevents
crashes in corner-cases of various set operations where the set gets
mutated.

- bpo-45828: The bytecode compiler now attempts to apply runtime stack
manipulations at compile-time (whenever it is feasible to do so).

- bpo-30496: Fixed a minor portability issue in the implementation of
:c:func:`PyLong_FromLong`, and added a fast path for single-digit integers
to :c:func:`PyLong_FromLongLong`.

Library
-------

- bpo-25707: Fixed a file leak in :func:`xml.etree.ElementTree.iterparse`
when the iterator is not exhausted. Patch by Jacob Walls.

- bpo-46877: Export :func:`unittest.doModuleCleanups` in :mod:`unittest`.
Patch by Kumar Aditya.

- bpo-46848: For performance, use the optimized string-searching
implementations from :meth:`~bytes.find` and :meth:`~bytes.rfind` for
:meth:`~mmap.find` and :meth:`~mmap.rfind`.

- bpo-46736: :class:`~http.server.SimpleHTTPRequestHandler` now uses HTML5
grammar. Patch by Dong-hee Na.

- bpo-44886: Inherit asyncio proactor datagram transport from
:class:`asyncio.DatagramTransport`.

- bpo-46827: Support UDP sockets in :meth:`asyncio.loop.sock_connect` for
selector-based event loops. Patch by Thomas Grainger.

- bpo-46811: Make test suite support Expat >=2.4.5

- bpo-46252: Raise :exc:`TypeError` if :class:`ssl.SSLSocket` is passed to
transport-based APIs.

- bpo-46784: Fix libexpat symbols collisions with user dynamically loaded or
statically linked libexpat in embedded Python.

- bpo-46786: The HTML serialisation in xml.etree.ElementTree now writes
``embed``, ``source``, ``track`` and ``wbr`` as empty tags, as defined in
HTML 5.

- bpo-39327: :func:`shutil.rmtree` can now work with VirtualBox shared
folders when running from the guest operating-system.

- bpo-45390: Propagate :exc:`asyncio.CancelledError` message from inner task
to outer awaiter.

- bpo-46756: Fix a bug in
:meth:`urllib.request.HTTPPasswordMgr.find_user_password` and
:meth:`urllib.request.HTTPPasswordMgrWithPriorAuth.is_authenticated` which
allowed to bypass authorization. For example, access to URI
``example.org/foobar`` was allowed if the user was authorized for URI
``example.org/foo``.

- bpo-46737: :func:`random.gauss` and :func:`random.normalvariate` now have
default arguments.

- bpo-46752: Add task groups to asyncio (structured concurrency, inspired by
Trio's nurseries). This also introduces a change to task cancellation,
where a cancelled task can't be cancelled again until it calls
.uncancel().

- bpo-46724: Fix :mod:`dis` behavior on negative jump offsets.

- bpo-46333: The :meth:`__repr__` method of :class:`typing.ForwardRef` now
includes the ``module`` parameter of :class:`typing.ForwardRef` when it is
set.

- bpo-46643: In :func:`typing.get_type_hints`, support evaluating
stringified ``ParamSpecArgs`` and ``ParamSpecKwargs`` annotations. Patch
by Gregory Beauregard.

- bpo-45863: When the :mod:`tarfile` module creates a pax format archive, it
will put an integer representation of timestamps in the ustar header (if
possible) for the benefit of older unarchivers, in addition to the
existing full-precision timestamps in the pax extended header.

- bpo-46066: Deprecate kwargs-based syntax for :class:`typing.TypedDict`
definitions. It had confusing semantics when specifying totality, and was
largely unused. Patch by Jingchen Ye.

- bpo-46676: Make :data:`typing.ParamSpec` args and kwargs equal to
themselves. Patch by Gregory Beauregard.

- bpo-46323: ``ctypes.CFUNCTYPE()`` and ``ctypes.WINFUNCTYPE()`` now fail to
create the type if its ``_argtypes_`` member contains too many arguments.
Previously, the error was only raised when calling a function. Patch by
Victor Stinner.

- bpo-46672: Fix ``NameError`` in :func:`asyncio.gather` when initial type
check fails.

- bpo-46659: The :class:`calendar.LocaleTextCalendar` and
:class:`calendar.LocaleHTMLCalendar` classes now use
:func:`locale.getlocale`, instead of using
:func:`locale.getdefaultlocale`, if no locale is specified. Patch by
Victor Stinner.

- bpo-46659: The :func:`locale.getdefaultlocale` function is deprecated and
will be removed in Python 3.13. Use :func:`locale.setlocale`,
:func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`
and :func:`locale.getlocale` functions instead. Patch by Victor Stinner.

- bpo-46655: In :func:`typing.get_type_hints`, support evaluating bare
stringified ``TypeAlias`` annotations. Patch by Gregory Beauregard.

- bpo-45948: Fixed a discrepancy in the C implementation of the
:mod:`xml.etree.ElementTree` module. Now, instantiating an
:class:`xml.etree.ElementTree.XMLParser` with a ``target=None`` keyword
provides a default :class:`xml.etree.ElementTree.TreeBuilder` target as
the Python implementation does.

- bpo-46626: Expose Linux's ``IP_BIND_ADDRESS_NO_PORT`` option in
:mod:`socket`.

- bpo-46521: Fix a bug in the :mod:`codeop` module that was incorrectly
identifying invalid code involving string quotes as valid code.

- bpo-46571: Improve :func:`typing.no_type_check`.

Now it does not modify external classes and functions. We also now
correctly mark classmethods as not to be type checked.

- bpo-46400: expat: Update libexpat from 2.4.1 to 2.4.4

- bpo-46556: Deprecate undocumented support for using a
:class:`pathlib.Path` object as a context manager.

- bpo-46534: Implement :pep:`673` :class:`typing.Self`. Patch by James
Hilton-Balfe.

- bpo-46522: Make various module ``__getattr__`` AttributeErrors more
closely match a typical AttributeError

- bpo-46475: Add :data:`typing.Never` and :func:`typing.assert_never`. Patch
by Jelle Zijlstra.

- bpo-46333: The :meth:`__eq__` and :meth:`__hash__` methods of
:class:`typing.ForwardRef` now honor the ``module`` parameter of
:class:`typing.ForwardRef`. Forward references from different modules are
now differentiated.

- bpo-46246: Add missing ``__slots__`` to
``importlib.metadata.DeprecatedList``. Patch by Arie Bovenberg.

- bpo-46232: The :mod:`ssl` module now handles certificates with bit strings
in DN correctly.

- bpo-46195: :func:`typing.get_type_hints` no longer adds ``Optional`` to
parameters with ``None`` as a default. This aligns to changes to PEP 484
in https://github.com/python/peps/pull/689

- bpo-31369: Add :class:`~re.RegexFlag` to ``re.__all__`` and documented it.
Add :data:`~re.RegexFlag.NOFLAG` to indicate no flags being set.

- bpo-45898: :mod:`ctypes` no longer defines ``ffi_type_*`` symbols in
``cfield.c``. The symbols have been provided by libffi for over a decade.

- bpo-44953: Calling ``operator.itemgetter`` objects and
``operator.attrgetter`` objects is now faster due to use of the vectorcall
calling convention.

- bpo-44289: Fix an issue with :meth:`~tarfile.is_tarfile` method when using
*fileobj* argument: position in the *fileobj* was advanced forward which
made it unreadable with :meth:`tarfile.TarFile.open`.

- bpo-44011: Reimplement SSL/TLS support in asyncio, borrow the
implementation from uvloop library.

- bpo-41086: Make the :class:`configparser.ConfigParser` constructor raise
:exc:`TypeError` if the ``interpolation`` parameter is not of type
:class:`configparser.Interpolation`

- bpo-29418: Implement :func:`inspect.ismethodwrapper` and fix
:func:`inspect.isroutine` for cases where methodwrapper is given. Patch by
Hakan Çelik.

- bpo-14156: argparse.FileType now supports an argument of '-' in binary
mode, returning the .buffer attribute of sys.stdin/sys.stdout as
appropriate. Modes including 'x' and 'a' are treated equivalently to 'w'
when argument is '-'. Patch contributed by Josh Rosenberg

Documentation
-------------

- bpo-42238: ``Doc/tools/rstlint.py`` has moved to its own repository and is
now packaged on PyPI as ``sphinx-lint``.

Tests
-----

- bpo-46913: Fix test_faulthandler.test_sigfpe() if Python is built with
undefined behavior sanitizer (UBSAN): disable UBSAN on the
faulthandler_sigfpe() function. Patch by Victor Stinner.

- bpo-46760: Remove bytecode offsets from expected values in test.test_dis
module. Reduces the obstacles to modifying the VM or compiler.

- bpo-46708: Prevent default asyncio event loop policy modification warning
after ``test_asyncio`` execution.

- bpo-46678: The function ``make_legacy_pyc`` in
``Lib/test/support/import_helper.py`` no longer fails when
``PYTHONPYCACHEPREFIX`` is set to a directory on a different device from
where tempfiles are stored.

- bpo-46623: Skip test_pair() and test_speech128() of test_zlib on s390x
since they fail if zlib uses the s390x hardware accelerator. Patch by
Victor Stinner.

Build
-----

- bpo-46860: Respect `--with-suffix` when building on case-insensitive file
systems.

- bpo-46656: Building Python now requires a C11 compiler. Optional C11
features are not required. Patch by Victor Stinner.

- bpo-46656: Building Python now requires support for floating point
Not-a-Number (NaN): remove the ``Py_NO_NAN`` macro. Patch by by Victor
Stinner.

- bpo-46640: Building Python now requires a C99 ``<math.h>`` header file
providing a ``NAN`` constant, or the ``__builtin_nan()`` built-in
function. Patch by Victor Stinner.

- bpo-46608: Exclude marshalled-frozen data if deep-freezing to save 300 KB
disk space. This includes adding a new ``is_package`` field to
:c:struct:`_frozen`. Patch by Kumar Aditya.

- bpo-40280: Fix wasm32-emscripten test failures and platform issues. -
Disable syscalls that are not supported or don't work, e.g. wait,
getrusage, prlimit, mkfifo, mknod, setres[gu]id, setgroups. - Use fd_count
to cound open fds. - Add more checks for subprocess and fork. - Add
workarounds for missing _multiprocessing and failing socket.accept(). -
Enable bzip2. - Disable large file support. - Disable signal.alarm.

- bpo-46430: Intern strings in deep-frozen modules. Patch by Kumar Aditya.

Windows
-------

- bpo-46744: The default all users install directory for ARM64 is now under
the native ``Program Files`` folder, rather than ``Program Files (Arm)``
which is intended for ARM (32-bit) files.

- bpo-46567: Adds Tcl and Tk support for Windows ARM64. This also adds IDLE
to the installation.

- bpo-46638: Ensures registry virtualization is consistently disabled. For
3.10 and earlier, it remains enabled (some registry writes are protected),
while for 3.11 and later it is disabled (registry modifications affect all
applications).

IDLE
----

- bpo-46630: Make query dialogs on Windows start with a cursor in the entry
box.

- bpo-45447: Apply IDLE syntax highlighting to `.pyi` files. Patch by Alex
Waygood and Terry Jan Reedy.

C API
-----

- bpo-46748: Python's public headers no longer import ``<stdbool.h>``,
leaving code that embedd/extends Python free to define ``bool``, ``true``
and ``false``.

- bpo-46836: Move the :c:type:`PyFrameObject` type definition (``struct
_frame``) to the internal C API ``pycore_frame.h`` header file. Patch by
Victor Stinner.

- bpo-45459: Rename ``Include/buffer.h`` header file to
``Include/pybuffer.h`` to avoid conflits with projects having an existing
``buffer.h`` header file. Patch by Victor Stinner.

- bpo-45412: Remove the ``HAVE_PY_SET_53BIT_PRECISION`` macro (moved to the
internal C API). Patch by Victor Stinner.

- bpo-46613: Added function :c:func:`PyType_GetModuleByDef`, which allows
accesss to module state when a method's defining class is not available.

What's New in Python 3.11.0 alpha 5?
====================================

*Release date: 2022-02-03*

Core and Builtins
-----------------

- bpo-45773: Remove two invalid "peephole" optimizations from the bytecode
compiler.

- bpo-46564: Do not create frame objects when creating :class:`super`
object. Patch by Kumar Aditya.

- bpo-45885: Added more fined-grained specialization failure stats regarding
the ``COMPARE_OP`` bytecode.

- bpo-44977: The delegation of :func:`int` to :meth:`__trunc__` is now
deprecated. Calling ``int(a)`` when ``type(a)`` implements
:meth:`__trunc__` but not :meth:`__int__` or :meth:`__index__` now raises
a :exc:`DeprecationWarning`.

- bpo-46458: Reorder code emitted by the compiler for a
:keyword:`try`-:keyword:`except` block so that the :keyword:`else` block's
code immediately follows the :keyword:`try` body (without a jump). This is
more optimal for the happy path.

- bpo-46527: Allow passing ``iterable`` as a keyword argument to
:func:`enumerate` again. Patch by Jelle Zijlstra.

- bpo-46528: Replace several stack manipulation instructions (``DUP_TOP``,
``DUP_TOP_TWO``, ``ROT_TWO``, ``ROT_THREE``, ``ROT_FOUR``, and ``ROT_N``)
with new :opcode:`COPY` and :opcode:`SWAP` instructions.

- bpo-46329: Use two or three bytecodes to implement most calls.

Calls without named arguments are implemented as a sequence of two
instructions: ``PRECALL; CALL``. Calls with named arguments are
implemented as a sequence of three instructions: ``PRECALL; KW_NAMES;
CALL``. There are two different ``PRECALL`` instructions:
``PRECALL_FUNTION`` and ``PRECALL_METHOD``. The latter pairs with
``LOAD_METHOD``.

This partition into pre-call and call allows better specialization, and
thus better performance ultimately.

There is no change in semantics.

- bpo-46503: Fix an assert when parsing some invalid \N escape sequences in
f-strings.

- bpo-46431: Improve error message on invalid calls to
:meth:`BaseExceptionGroup.__new__`.

- bpo-46476: Fix memory leak in code objects generated by deepfreeze. Patch
by Kumar Aditya.

- bpo-46481: Speed up calls to :meth:`weakref.ref.__call__` by using the
:pep:`590` ``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-46417: Fix a race condition on setting a type ``__bases__`` attribute:
the internal function ``add_subclass()`` now gets the
``PyTypeObject.tp_subclasses`` member after calling
:c:func:`PyWeakref_NewRef` which can trigger a garbage collection which
can indirectly modify ``PyTypeObject.tp_subclasses``. Patch by Victor
Stinner.

- bpo-46417: ``python -X showrefcount`` now shows the total reference count
after clearing and destroyed the main Python interpreter. Previously, it
was shown before. Patch by Victor Stinner.

- bpo-43683: Add ASYNC_GEN_WRAP opcode to wrap the value to be yielded in
async generators. Removes the need to special case async generators in the
``YIELD_VALUE`` instruction.

- bpo-46407: Optimize some modulo operations in ``Objects/longobject.c``.
Patch by Jeremiah Vivian.

- bpo-46409: Add new ``RETURN_GENERATOR`` bytecode to make generators.
Simplifies calling Python functions in the VM, as they no longer any need
to special case generator functions.

Also add ``JUMP_NO_INTERRUPT`` bytecode that acts like ``JUMP_ABSOLUTE``,
but does not check for interrupts.

- bpo-46406: The integer division ``//`` implementation has been optimized
to better let the compiler understand its constraints. It can be 20%
faster on the amd64 platform when dividing an int by a value smaller than
``2**30``.

- bpo-46383: Fix invalid signature of ``_zoneinfo``'s ``module_free``
function to resolve a crash on wasm32-emscripten platform.

- bpo-46361: Ensure that "small" integers created by :meth:`int.from_bytes`
and :class:`decimal.Decimal` are properly cached.

- bpo-46161: Fix the class building error when the arguments are constants
and CALL_FUNCTION_EX is used.

- bpo-46028: Fixes calculation of :data:`sys._base_executable` when inside a
virtual environment that uses symlinks with different binary names than
the base environment provides.

- bpo-46091: Correctly calculate indentation levels for lines with
whitespace character that are ended by line continuation characters. Patch
by Pablo Galindo

- bpo-30512: Add CAN Socket support for NetBSD.

- bpo-46045: Do not use POSIX semaphores on NetBSD

- bpo-44024: Improve the exc:`TypeError` message for non-string second
arguments passed to the built-in functions :func:`getattr` and
:func:`hasattr`. Patch by Géry Ogam.

Library
-------

- bpo-46624: Restore support for non-integer arguments of
:func:`random.randrange` and :func:`random.randint`.

- bpo-46591: Make the IDLE doc URL on the About IDLE dialog clickable.

- bpo-46565: Remove loop variables that are leaking into modules'
namespaces.

- bpo-46553: In :func:`typing.get_type_hints`, support evaluating bare
stringified ``ClassVar`` annotations. Patch by Gregory Beauregard.

- bpo-46544: Don't leak ``x`` & ``uspace`` intermediate vars in
:class:`textwrap.TextWrapper`.

- bpo-46487: Add the ``get_write_buffer_limits`` method to
:class:`asyncio.transports.WriteTransport` and to the SSL transport.

- bpo-45173: Note the configparser deprecations will be removed in Python
3.12.

- bpo-45162: The deprecated :mod:`unittest` APIs removed in 3.11a1 have been
temporarily restored to be removed in 3.12 while cleanups in external
projects go in.

- bpo-46539: In :func:`typing.get_type_hints`, support evaluating
stringified ``ClassVar`` and ``Final`` annotations inside ``Annotated``.
Patch by Gregory Beauregard.

- bpo-46510: Add missing test for :class:`types.TracebackType` and
:class:`types.FrameType`. Calculate them directly from the caught
exception without calling :func:`sys.exc_info`.

- bpo-46491: Allow :data:`typing.Annotated` to wrap :data:`typing.Final` and
:data:`typing.ClassVar`. Patch by Gregory Beauregard.

- bpo-46483: Remove :meth:`~object.__class_getitem__` from
:class:`pathlib.PurePath` as this class was not supposed to be generic.

- bpo-46436: Fix command-line option ``-d``/``--directory`` in module
:mod:`http.server` which is ignored when combined with command-line option
``--cgi``. Patch by Géry Ogam.

- bpo-41403: Make :meth:`mock.patch` raise a :exc:`TypeError` with a
relevant error message on invalid arg. Previously it allowed a cryptic
:exc:`AttributeError` to escape.

- bpo-46474: In ``importlib.metadata.EntryPoint.pattern``, avoid potential
REDoS by limiting ambiguity in consecutive whitespace.

- bpo-46474: Removed private method from ``importlib.metadata.Path``. Sync
with importlib_metadata 4.10.0.

- bpo-46470: Remove unused branch from ``typing._remove_dups_flatten``

- bpo-46469: :mod:`asyncio` generic classes now return
:class:`types.GenericAlias` in ``__class_getitem__`` instead of the same
class.

- bpo-41906: Support passing filter instances in the ``filters`` values of
``handlers`` and ``loggers`` in the dictionary passed to
:func:`logging.config.dictConfig`.

- bpo-46422: Use ``dis.Positions`` in ``dis.Instruction`` instead of a
regular ``tuple``.

- bpo-46434: :mod:`pdb` now gracefully handles ``help`` when :attr:`__doc__`
is missing, for example when run with pregenerated optimized ``.pyc``
files.

- bpo-43869: Python uses the same time Epoch on all platforms. Add an
explicit unit test to ensure that it's the case. Patch by Victor Stinner.

- bpo-46414: Add :func:`typing.reveal_type`. Patch by Jelle Zijlstra.

- bpo-40280: :mod:`subprocess` now imports Windows-specific imports when
``msvcrt`` module is available, and POSIX-specific imports on all other
platforms. This gives a clean exception when ``_posixsubprocess`` is not
available (e.g. Emscripten browser target).

- bpo-40066: ``IntEnum``, ``IntFlag``, and ``StrEnum`` use the mixed-in type
for their ``str()`` and ``format()`` output.

- bpo-46316: Optimize :meth:`pathlib.Path.iterdir` by removing an
unnecessary check for special entries.

- bpo-29688: Document :meth:`pathlib.Path.absolute` (which has always
existed).

- bpo-43012: The pathlib module's obsolete and internal ``_Accessor`` class
has been removed to prepare the terrain for upcoming enhancements to the
module.

- bpo-46258: Speed up :func:`math.isqrt` for small positive integers by
replacing two division steps with a lookup table.

- bpo-46242: Improve error message when creating a new :class:`enum.Enum`
type subclassing an existing ``Enum`` with ``_member_names_`` using
:meth:`enum.Enum.__call__`.

- bpo-43118: Fix a bug in :func:`inspect.signature` that was causing it to
fail on some subclasses of classes with a ``__text_signature__``
referencing module globals. Patch by Weipeng Hong.

- bpo-26552: Fixed case where failing :func:`asyncio.ensure_future` did not
close the coroutine. Patch by Kumar Aditya.

- bpo-21987: Fix an issue with :meth:`tarfile.TarFile.getmember` getting a
directory name with a trailing slash.

- bpo-46124: Update :mod:`zoneinfo` to rely on importlib.resources
traversable API.

- bpo-46103: Now :func:`inspect.getmembers` only gets :attr:`__bases__`
attribute from class type. Patch by Weipeng Hong.

- bpo-46080: Fix exception in argparse help text generation if a
:class:`argparse.BooleanOptionalAction` argument's default is
``argparse.SUPPRESS`` and it has ``help`` specified. Patch by Felix
Fontein.

- bpo-44791: Fix substitution of :class:`~typing.ParamSpec` in
:data:`~typing.Concatenate` with different parameter expressions.
Substitution with a list of types returns now a tuple of types.
Substitution with ``Concatenate`` returns now a ``Concatenate`` with
concatenated lists of arguments.

Documentation
-------------

- bpo-46463: Fixes :file:`escape4chm.py` script used when building the CHM
documentation file

Tests
-----

- bpo-43478: Mocks can no longer be provided as the specs for other Mocks.
As a result, an already-mocked object cannot be passed to `mock.Mock()`.
This can uncover bugs in tests since these Mock-derived Mocks will always
pass certain tests (e.g. isinstance) and builtin assert functions (e.g.
assert_called_once_with) will unconditionally pass.

- bpo-46616: Ensures ``test_importlib.test_windows`` cleans up registry keys
after completion.

- bpo-44359: test_ftplib now silently ignores socket errors to prevent
logging unhandled threading exceptions. Patch by Victor Stinner.

- bpo-46600: Fix test_gdb.test_pycfunction() for Python built with ``clang
-Og``. Tolerate inlined functions in the gdb traceback. Patch by Victor
Stinner.

- bpo-46542: Fix a Python crash in test_lib2to3 when using Python built in
debug mode: limit the recursion limit. Patch by Victor Stinner.

- bpo-46576: test_peg_generator now disables compiler optimization when
testing compilation of its own C extensions to significantly speed up the
testing on non-debug builds of CPython.

- bpo-46542: Fix ``test_json`` tests checking for :exc:`RecursionError`:
modify these tests to use ``support.infinite_recursion()``. Patch by
Victor Stinner.

- bpo-13886: Skip test_builtin PTY tests on non-ASCII characters if the
readline module is loaded. The readline module changes input() behavior,
but test_builtin is not intented to test the readline module. Patch by
Victor Stinner.

- bpo-40280: Add :func:`test.support.requires_fork` decorators to mark tests
that require a working :func:`os.fork`.

- bpo-40280: Add :func:`test.support.requires_subprocess` decorator to mark
tests which require working :mod:`subprocess` module or ``os.spawn*``. The
wasm32-emscripten platform has no support for processes.

- bpo-46126: Disable 'descriptions' when running tests internally.

Build
-----

- bpo-46602: Tidied up configure.ac so that conftest.c is truncated rather
than appended. This assists in the case where the 'rm' of conftest.c fails
to happen between tests. Downstream issues such as a clobbered SOABI can
result.

- bpo-46600: Fix the test checking if the C compiler supports ``-Og`` option
in the ``./configure`` script to also use ``-Og`` on clang which supports
it. Patch by Victor Stinner.

- bpo-38472: Fix GCC detection in setup.py when cross-compiling. The C
compiler is now run with LC_ALL=C. Previously, the detection failed with a
German locale.

- bpo-46513: :program:`configure` no longer uses ``AC_C_CHAR_UNSIGNED``
macro and ``pyconfig.h`` no longer defines reserved symbol
``__CHAR_UNSIGNED__``.

- bpo-46471: Use global singletons for single byte bytes objects in
deepfreeze.

- bpo-46443: Deepfreeze now uses cached small integers as it saves some
space for common small integers.

- bpo-46429: Merge all deep-frozen files into one for space savings. Patch
by Kumar Aditya.

- bpo-45569: The build now defaults to using 30-bit digits for Python
integers. Previously either 15-bit or 30-bit digits would be selected,
depending on the platform. 15-bit digits may still be selected using the
``--enable-big-digits=15`` option to the ``configure`` script, or by
defining ``PYLONG_BITS_IN_DIGIT`` in ``pyconfig.h``.

- bpo-45925: Update Windows installer to use SQLite 3.37.2.

- bpo-43112: Detect musl libc as a separate SOABI (tagged as
``linux-musl``).

Windows
-------

- bpo-33125: The traditional EXE/MSI based installer for Windows is now
available for ARM64

- bpo-46362: os.path.abspath("C:\CON") is now fixed to return "\\.\CON", not
the same path. The regression was true of all legacy DOS devices such as
COM1, LPT1, or NUL.

- bpo-44934: The installer now offers a command-line only option to add the
installation directory to the end of :envvar:`PATH` instead of at the
start.

macOS
-----

- bpo-45925: Update macOS installer to SQLite 3.37.2.

IDLE
----

- bpo-45296: Clarify close, quit, and exit in IDLE. In the File menu,
'Close' and 'Exit' are now 'Close Window' (the current one) and 'Exit' is
now 'Exit IDLE' (by closing all windows). In Shell, 'quit()' and 'exit()'
mean 'close Shell'. If there are no other windows, this also exits IDLE.

C API
-----

- bpo-40170: Remove the ``PyHeapType_GET_MEMBERS()`` macro. It was exposed
in the public C API by mistake, it must only be used by Python internally.
Use the ``PyTypeObject.tp_members`` member instead. Patch by Victor
Stinner.

- bpo-40170: Move _Py_GetAllocatedBlocks() and _PyObject_DebugMallocStats()
private functions to the internal C API. Patch by Victor Stinner.

- bpo-46433: The internal function _PyType_GetModuleByDef now correctly
handles inheritance patterns involving static types.

- bpo-45459: :c:type:`Py_buffer` and various ``Py_buffer`` related functions
are now part of the limited API and stable ABI.

- bpo-14916: Fixed bug in the tokenizer that prevented
``PyRun_InteractiveOne`` from parsing from the provided FD.

What's New in Python 3.11.0 alpha 4?
====================================

*Release date: 2022-01-13*

Core and Builtins
-----------------

- bpo-46070: :c:func:`Py_EndInterpreter` now explicitly untracks all objects
currently tracked by the GC. Previously, if an object was used later by
another interpreter, calling :c:func:`PyObject_GC_UnTrack` on the object
crashed if the previous or the next object of the :c:type:`PyGC_Head`
structure became a dangling pointer. Patch by Victor Stinner.

- bpo-46347: Fix memory leak in PyEval_EvalCodeEx.

- bpo-46339: Fix a crash in the parser when retrieving the error text for
multi-line f-strings expressions that do not start in the first line of
the string. Patch by Pablo Galindo

- bpo-46331: Do not set line number of instruction storing doc-string. Fixes
regression introduced in 3.11 alpha.

- bpo-46314: Remove spurious "call" event when creating a lambda function
that was accidentally introduced in 3.11a4.

- bpo-46289: ASDL declaration of ``FormattedValue`` has changed to reflect
``conversion`` field is not optional.

- bpo-46297: Fixed an interpreter crash on bootup with multiple PythonPaths
set in the Windows registry. Patch by Derzsi Dániel.

- bpo-46237: Fix the line number of tokenizer errors inside f-strings. Patch
by Pablo Galindo.

- bpo-46263: We always expect the "use_frozen_modules" config to be set, now
that getpath.c was rewritten in pure Python and the logic improved.

- bpo-46006: Fix a regression when a type method like ``__init__()`` is
modified in a subinterpreter. Fix a regression in
``_PyUnicode_EqualToASCIIId()`` and type ``update_slot()``. Revert the
change which made the Unicode dictionary of interned strings compatible
with subinterpreters: the internal interned dictionary is shared again by
all interpreters. Patch by Victor Stinner.

- bpo-45923: Add RESUME opcode. This is a logical no-op. It is emitted by
the compiler anywhere a Python function can be entered. It is used by the
interpreter to perform tracing and optimizer checks.

- bpo-46208: Fix the regression of os.path.normpath("A/../../B") not
returning expected "../B" but "B".

- bpo-46240: Correct the error message for unclosed parentheses when the
tokenizer doesn't reach the end of the source when the error is reported.
Patch by Pablo Galindo

- bpo-46009: Remove the ``GEN_START`` opcode.

- bpo-46235: Certain sequence multiplication operations like ``[0] * 1_000``
are now faster due to reference-counting optimizations. Patch by Dennis
Sweeney.

- bpo-46221: :opcode:`PREP_RERAISE_STAR` no longer pushes ``lasti`` to the
stack.

- bpo-46202: Remove :opcode:`POP_EXCEPT_AND_RERAISE` and replace it by an
equivalent sequence of other opcodes.

- bpo-46085: Fix iterator cache mechanism of :class:`OrderedDict`.

- bpo-46055: Speed up shifting operation involving integers less than
:c:macro:`PyLong_BASE`. Patch by Xinhang Xu.

- bpo-46110: Add a maximum recursion check to the PEG parser to avoid stack
overflow. Patch by Pablo Galindo

- bpo-46107: Fix bug where :meth:`ExceptionGroup.split` and
:meth:`ExceptionGroup.subgroup` did not copy the exception group's
``__note__`` field to the parts.

- bpo-45711: The interpreter state's representation of handled exceptions
(a.k.a exc_info, or _PyErr_StackItem) now has only the ``exc_value``
field, ``exc_type`` and ``exc_traceback`` have been removed as their
values can be derived from ``exc_value``.

- bpo-44525: Replace the four call bytecode instructions which one pre-call
instruction and two call instructions.

Removes ``CALL_FUNCTION``, ``CALL_FUNCTION_KW``, ``CALL_METHOD`` and
``CALL_METHOD_KW``.

Adds ``CALL_NO_KW`` and ``CALL_KW`` call instructions, and
``PRECALL_METHOD`` prefix for pairing with ``LOAD_METHOD``.

- bpo-46039: Remove the ``YIELD_FROM`` instruction and replace it with the
``SEND`` instruction which performs the same operation, but without the
loop.

- bpo-45635: The code called from :c:func:`_PyErr_Display` was refactored to
improve error handling. It now exits immediately upon an unrecoverable
error.

- bpo-46054: Fix parser error when parsing non-utf8 characters in source
files. Patch by Pablo Galindo.

- bpo-46042: Improve the location of the caret in :exc:`SyntaxError`
exceptions emitted by the symbol table. Patch by Pablo Galindo.

- bpo-46049: Ensure :file:`._pth` files work as intended on platforms other
than Windows.

- bpo-46048: Fixes parsing of :file:`._pth` files on startup so that
single-character paths are correctly read.

- bpo-37971: Fix a bug where the line numbers given in a traceback when a
decorator application raised an exception were wrong.

- bpo-46031: Add :opcode:`POP_JUMP_IF_NOT_NONE` and
:opcode:`POP_JUMP_IF_NONE` opcodes to speed up conditional jumps.

- bpo-45654: Deepfreeze :mod:`runpy`, patch by Kumar Aditya.

- bpo-46025: Fix a crash in the :mod:`atexit` module involving functions
that unregister themselves before raising exceptions. Patch by Pablo
Galindo.

- bpo-46000: Improve compatibility of the :mod:`curses` module with NetBSD
curses.

- bpo-44525: Specialize the CALL_FUNCTION instruction for calls to builtin
types with a single argument. Speeds up ``range(x)``, ``list(x)``, and
specifically ``type(obj)``.

- bpo-42918: Fix bug where the built-in :func:`compile` function did not
always raise a :exc:`SyntaxError` when passed multiple statements in
'single' mode. Patch by Weipeng Hong.

- bpo-45953: The main interpreter in _PyRuntimeState.interpreters is now
statically allocated (as part of _PyRuntime). Likewise for the initial
thread state of each interpreter. This means less allocation during
runtime init, as well as better memory locality for these key state
objects.

- bpo-45292: Complete the :pep:`654` implementation: add ``except*``.

- bpo-43413: Revert changes in ``set.__init__``. Subclass of :class:`set`
needs to define a ``__init__()`` method if it defines a ``__new__()``
method with additional keyword parameters.

- bpo-43931: Added the :c:data:`Py_Version` constant which bears the same
value as :c:macro:`PY_VERSION_HEX`. Patch by Gabriele N. Tornetta.

Library
-------

- bpo-46342: The ``@typing.final`` decorator now sets the ``__final__``
attribute on the decorated object to allow runtime introspection. Patch by
Jelle Zijlstra.

- bpo-46328: Added the :meth:`sys.exception` method which returns the active
exception instance.

- bpo-46307: Add :meth:`string.Template.is_valid` and
:meth:`string.Template.get_identifiers` methods.

- bpo-46306: Assume that :class:`types.CodeType` always has
:attr:`types.CodeType.co_firstlineno` in :mod:`doctest`.

- bpo-40479: Fix :mod:`hashlib` *usedforsecurity* option to work correctly
with OpenSSL 3.0.0 in FIPS mode.

- bpo-46070: Fix possible segfault when importing the :mod:`asyncio` module
from different sub-interpreters in parallel. Patch by Erlend E. Aasland.

- bpo-46244: Removed ``__slots__`` from :class:`typing.ParamSpec` and
:class:`typing.TypeVar`. They served no purpose. Patch by Arie Bovenberg.

- bpo-46278: Reflect ``context`` argument in ``AbstractEventLoop.call_*()``
methods. Loop implementations already support it.

- bpo-46269: Remove special-casing of ``__new__`` in
:meth:`enum.Enum.__dir__`.

- bpo-46266: Improve day constants in :mod:`calendar`.

Now all constants (`MONDAY` ... `SUNDAY`) are documented, tested, and
added to ``__all__``.

- bpo-46257: Optimized the mean, variance, and stdev functions in the
statistics module. If the input is an iterator, it is consumed in a single
pass rather than eating memory by conversion to a list. The single pass
algorithm is about twice as fast as the previous two pass code.

- bpo-41011: Added two new variables to *pyvenv.cfg* which is generated by
:mod:`venv` module: *executable* for the executable and *command* for the
command line used to create the environment.

- bpo-46239: Improve error message when importing
:mod:`asyncio.windows_events` on non-Windows.

- bpo-46238: Reuse ``_winapi`` constants in ``asyncio.windows_events``.

- bpo-46222: Adding ``SF_NOCACHE`` sendfile constant for FreeBSD for the
posixmodule.

- bpo-37295: Add fast path for ``0 <= k <= n <= 67`` for :func:`math.comb`.

- bpo-46176: Adding the ``MAP_STACK`` constant for the mmap module.

- bpo-43424: Deprecate :attr:`webbrowser.MacOSXOSAScript._name` and use
``name`` instead.

- bpo-45321: Added missing error codes to module
``xml.parsers.expat.errors``.

- bpo-46125: Refactor tests to test traversable API directly. Includes
changes from importlib 5.4.0.

- bpo-46118: Moved importlib.resources and its related functionality to a
package.

- bpo-37578: Add *include_hidden* parameter to :func:`~glob.glob` and
:func:`~glob.iglob` to match hidden files and directories when using
special characters like ``*``, ``**``, ``?`` and ``[]``.

- bpo-20369: :func:`concurrent.futures.wait` no longer blocks forever when
given duplicate Futures. Patch by Kumar Aditya.

- bpo-46105: Honor spec when generating requirement specs with urls and
extras (importlib_metadata 4.8.3).

- bpo-44893: EntryPoint objects are no longer tuples. Recommended means to
access is by attribute ('.name', '.group') or accessor ('.load()'). Access
by index is deprecated and will raise deprecation warning.

- bpo-22815: Print unexpected successes together with failures and errors in
summary in :class:`unittest.TextTestResult`.

- bpo-22047: Calling :meth:`add_argument_group` on an argument group is
deprecated. Calling :meth:`add_argument_group` or
:meth:`add_mutually_exclusive_group` on a mutually exclusive group is
deprecated.

These features were never supported and do not always work correctly. The
functions exist on the API by accident through inheritance and will be
removed in the future.

- bpo-26952: :mod:`argparse` raises :exc:`ValueError` with clear message
when trying to render usage for an empty mutually exclusive group.
Previously it raised a cryptic :exc:`IndexError`.

- bpo-45615: Functions in the :mod:`traceback` module raise :exc:`TypeError`
rather than :exc:`AttributeError` when an exception argument is not of
type :exc:`BaseException`.

- bpo-16594: Add allow allow_reuse_port flag in socketserver.

- bpo-27718: Fix help for the :mod:`signal` module. Some functions (e.g.
``signal()`` and ``getsignal()``) were omitted.

- bpo-46032: The ``registry()`` method of :func:`functools.singledispatch`
functions checks now the first argument or the first parameter annotation
and raises a TypeError if it is not supported. Previously unsupported
"types" were ignored (e.g. ``typing.List[int]``) or caused an error at
calling time (e.g. ``list[int]``).

- bpo-46014: Add ability to use ``typing.Union`` and ``types.UnionType`` as
dispatch argument to ``functools.singledispatch``. Patch provided by Yurii
Karabas.

- bpo-27062: Add :attr:`__all__` to :mod:`inspect`, patch by Kumar Aditya.

- bpo-46018: Ensure that :func:`math.expm1` does not raise on underflow.

- bpo-46016: Adding :attr:`F_DUP2FD` and :attr:`F_DUP2FD_CLOEXEC` constants
from FreeBSD into the fcntl module.

- bpo-45755: :mod:`typing` generic aliases now reveal the class attributes
of the original generic class when passed to ``dir()``. This was the
behavior up to Python 3.6, but was changed in 3.7-3.9.

- bpo-45874: The empty query string, consisting of no query arguments, is
now handled correctly in ``urllib.parse.parse_qsl``. This caused problems
before when strict parsing was enabled.

- bpo-44674: Change how dataclasses disallows mutable default values. It
used to use a list of known types (list, dict, set). Now it disallows
unhashable objects to be defaults. It's using unhashability as a proxy
for mutability. Patch by Eric V. Smith, idea by Raymond Hettinger.

- bpo-23882: Remove namespace package (PEP 420) support from unittest
discovery. It was introduced in Python 3.4 but has been broken since
Python 3.7.

- bpo-25066: Added a :meth:`__repr__` method to
:class:`multiprocessing.Event` objects, patch by Kumar Aditya.

- bpo-45643: Added :data:`signal.SIGSTKFLT` on platforms where this signal
is defined.

- bpo-44092: Fetch across rollback no longer raises
:exc:`~sqlite3.InterfaceError`. Instead we leave it to the SQLite library
to handle these cases. Patch by Erlend E. Aasland.

- bpo-42413: Replace ``concurrent.futures.TimeoutError`` and
``asyncio.TimeoutError`` with builtin :exc:`TimeoutError`, keep these
names as deprecated aliases.

Documentation
-------------

- bpo-46196: Document method :meth:`cmd.Cmd.columnize`.

- bpo-46120: State that ``|`` is preferred for readability over ``Union`` in
the :mod:`typing` docs.

- bpo-46109: Extracted ``importlib.resources`` and
``importlib.resources.abc`` documentation into separate files.

- bpo-19737: Update the documentation for the :func:`globals` function.

Tests
-----

- bpo-46296: Add a test case for :mod:`enum` with ``_use_args_ == True`` and
``_member_type_ == object``.

- bpo-46205: Fix hang in runtest_mp due to race condition

- bpo-46263: Fix test_capi on FreeBSD 14-dev: instruct jemalloc to not fill
freed memory with junk byte.

- bpo-46262: Cover ``ValueError`` path in tests for
:meth:`enum.Flag._missing_`.

- bpo-46150: Now ``fakename`` in
``test_pathlib.PosixPathTest.test_expanduser`` is checked to be
non-existent.

- bpo-46129: Rewrite ``asyncio.locks`` tests with
:class:`unittest.IsolatedAsyncioTestCase` usage.

- bpo-23819: Fixed :mod:`asyncio` tests in python optimized mode. Patch by
Kumar Aditya.

- bpo-46114: Fix test case for OpenSSL 3.0.1 version. OpenSSL 3.0 uses
``0xMNN00PP0L``.

Build
-----

- bpo-44133: When Python is configured with
:option:`--without-static-libpython`, the Python static library
(libpython.a) is no longer built. Patch by Victor Stinner.

- bpo-44133: When Python is built without :option:`--enable-shared`, the
``python`` program is now linked to object files, rather than being linked
to the Python static library (libpython.a), to make sure that all symbols
are exported. Previously, the linker omitted some symbols like the
:c:func:`Py_FrozenMain` function. Patch by Victor Stinner.

- bpo-40280: The ``configure`` script has a new option
``--with-emscripten-target`` to select browser or node as Emscripten build
target.

- bpo-46315: Added and fixed ``#ifdef HAVE_FEATURE`` checks for
functionality that is not available on WASI platform.

- bpo-45723: Fixed a regression in ``configure`` check for
:func:`select.epoll`.

- bpo-46263: ``configure`` no longer sets ``MULTIARCH`` on FreeBSD
platforms.

- bpo-46106: Updated OpenSSL to 1.1.1m in Windows builds, macOS installer
builds, and CI. Patch by Kumar Aditya.

- bpo-46088: Automatically detect or install bootstrap Python runtime when
building from Visual Studio.

- bpo-46072: Add a --with-pystats configure option to turn on internal
statistics gathering.

- bpo-40280: A new directory ``Tools/wasm`` contains WebAssembly-related
helpers like ``config.site`` override for wasm32-emscripten, wasm assets
generator to bundle the stdlib, and a README.

- bpo-46023: :program:`makesetup` no longer builds extensions that have been
marked as *disabled*. This allows users to disable modules in
``Modules/Setup.local``.

- bpo-45949: Use pure Python ``freeze_module`` for all but importlib
bootstrap files. ``--with-freeze-module`` :program:`configure` option is
no longer needed for cross builds.

Windows
-------

- bpo-46217: Removed parameter that is unsupported on Windows 8.1 and early
Windows 10 and may have caused build or runtime failures.

macOS
-----

- bpo-40477: The Python Launcher app for macOS now properly launches scripts
and, if necessary, the Terminal app when running on recent macOS releases.

C API
-----

- bpo-46236: Fix a bug in :c:func:`PyFunction_GetAnnotations` that caused it
to return a ``tuple`` instead of a ``dict``.

- bpo-46140: :c:func:`PyBuffer_GetPointer`,
:c:func:`PyBuffer_FromContiguous`, :c:func:`PyBuffer_ToContiguous` and
:c:func:`PyMemoryView_FromBuffer` now take buffer info by ``const
Py_buffer *`` instead of ``Py_buffer *``, as they do not need mutability.
:c:func:`PyBuffer_FromContiguous` also now takes the source buffer as
``const void *``, and similarly :c:func:`PyBuffer_GetPointer` takes the
strides as ``const Py_ssize_t *``.

- bpo-45855: Document that the *no_block* argument to
:c:func:`PyCapsule_Import` is a no-op now.

- bpo-45855: Replaced deprecated usage of
:c:func:`PyImport_ImportModuleNoBlock` with
:c:func:`PyImport_ImportModule` in stdlib modules. Patch by Kumar Aditya.

- bpo-46007: The :c:func:`PyUnicode_CHECK_INTERNED` macro has been excluded
from the limited C API. It was never usable there, because it used
internal structures which are not available in the limited C API. Patch by
Victor Stinner.

What's New in Python 3.11.0 alpha 3?
====================================

*Release date: 2021-12-08*

Core and Builtins
-----------------

- bpo-46009: Restore behavior from 3.9 and earlier when sending non-None to
newly started generator. In 3.9 this did not affect the state of the
generator. In 3.10.0 and 3.10.1 ``gen_func().send(0)`` is equivalent to
``gen_func().throw(TypeError(...)`` which exhausts the generator. In
3.10.2 onward, the behavior has been reverted to that of 3.9.

- bpo-46004: Fix the :exc:`SyntaxError` location for errors involving for
loops with invalid targets. Patch by Pablo Galindo

- bpo-45711: :c:func:`_PyErr_ChainStackItem` no longer normalizes
``exc_info`` (including setting the traceback on the exception instance)
because ``exc_info`` is always normalized.

- bpo-45607: The ``__note__`` field was added to :exc:`BaseException`. It is
``None`` by default but can be set to a string which is added to the
exception's traceback.

- bpo-45947: Place pointers to dict and values immediately before GC header.
This reduces number of dependent memory loads to access either dict or
values from 3 to 1.

- bpo-45915: ``is_valid_fd`` now uses faster ``fcntl(fd, F_GETFD)`` on
Linux, macOS, and Windows.

- bpo-44530: Reverts a change to the ``code.__new__`` :ref:`audit event
<audit-events>` from an earlier prerelease.

- bpo-42268: Fail the configure step if the selected compiler doesn't
support memory sanitizer. Patch by Pablo Galindo

- bpo-45711: The three values of ``exc_info`` are now always consistent with
each other. In particular, the ``type`` and ``traceback`` fields are now
derived from the exception instance. This impacts the return values of
:func:`sys.exc_info` and :c:func:`PyErr_GetExcInfo()` if the exception
instance is modified while the exception is handled, as well as
:c:func:`PyErr_SetExcInfo()`, which now ignores the ``type`` and
``traceback`` arguments provided to it.

- bpo-45727: Refine the custom syntax error that suggests that a comma may
be missing to trigger only when the expressions are detected between
parentheses or brackets. Patch by Pablo Galindo

- bpo-45885: Specialized the ``COMPARE_OP`` opcode using the PEP 659
machinery.

- bpo-45786: Allocate space for the interpreter frame in the frame object,
to avoid an additional allocation when the frame object outlives the frame
activation.

- bpo-45614: Fix :mod:`traceback` display for exceptions with invalid module
name.

- bpo-45813: Fix crash when calling coro.cr_frame.clear() after coroutine
has been freed.

- bpo-45811: Improve the tokenizer errors when encountering invisible
control characters in the parser. Patch by Pablo Galindo

- bpo-45848: Allow the parser to obtain error lines directly from encoded
files. Patch by Pablo Galindo

- bpo-45709: Restore behavior from 3.10 when tracing an exception raised
within a with statement.

- bpo-44525: Adds new :opcode:`COPY_FREE_VARS` opcode, to make copying of
free variables from function to frame explicit. Helps optimization of
calls to Python function.

- bpo-45829: Specialize :opcode:`BINARY_SUBSCR` for classes with a
``__getitem__`` method implemented in Python

- bpo-45826: Fixed a crash when calling ``.with_traceback(None)`` on
``NameError``. This occurs internally in
``unittest.TestCase.assertRaises()``.

- bpo-45822: Fixed a bug in the parser that was causing it to not respect
:pep:`263` coding cookies when no flags are provided. Patch by Pablo
Galindo

- bpo-45820: Fix a segfault when the parser fails without reading any input.
Patch by Pablo Galindo

- bpo-45636: Simplify the implementation of :opcode:`BINARY_OP` by indexing
into an array of function pointers (rather than switching on the oparg).

- bpo-42540: Fix crash when :func:`os.fork` is called with an active
non-default memory allocator.

- bpo-45738: Fix computation of error location for invalid continuation
characters in the parser. Patch by Pablo Galindo.

- bpo-45636: Remove an existing "fast path" for old-style string formatting,
since it no longer appears to have any measurable impact.

- bpo-45753: Make recursion checks a bit more efficient by tracking amount
of calls left before overflow.

- bpo-45773: Fix a compiler hang when attempting to optimize certain jump
patterns.

- bpo-45764: The parser now gives a better error message when leaving out
the opening parenthesis ``(`` after a ``def``-statement::

>>> def f:
File "<stdin>", line 1
def f:
^
SyntaxError: expected '('

- bpo-45609: Specialized the ``STORE_SUBSCR`` opcode using the PEP 659
machinery.

- bpo-45636: Replace all numeric ``BINARY_*`` and ``INPLACE_*`` instructions
with a single :opcode:`BINARY_OP` implementation.

- bpo-45582: Path calculation (known as ``getpath``) has been reimplemented
as a frozen Python module. This should have no visible impact, but may
affect calculation of all paths referenced in :mod:`sys` and
:mod:`sysconfig`.

- bpo-45450: Improve the syntax error message for parenthesized arguments.
Patch by Pablo Galindo.

Library
-------

- bpo-27946: Fix possible crash when getting an attribute of
class:`xml.etree.ElementTree.Element` simultaneously with replacing the
``attrib`` dict.

- bpo-45711: Make :mod:`asyncio` normalize exceptions as soon as they are
captured with :c:func:`PyErr_Fetch`, and before they are stored as an
exc_info triplet. This brings :mod:`asyncio` in line with the rest of the
codebase, where an exc_info triplet is always normalized.

- bpo-23819: Replaced asserts with exceptions in asyncio, patch by Kumar
Aditya.

- bpo-13236: :class:`unittest.TextTestResult` and
:class:`unittest.TextTestRunner` flush now the output stream more often.

- bpo-45917: Added :func:`math.exp2`:, which returns 2 raised to the power
of x.

- bpo-37658: Fix issue when on certain conditions ``asyncio.wait_for()`` may
allow a coroutine to complete successfully, but fail to return the result,
potentially causing memory leaks or other issues.

- bpo-45876: Improve the accuracy of stdev() and pstdev() in the statistics
module. When the inputs are floats or fractions, the output is a
correctly rounded float

- bpo-44649: Handle dataclass(slots=True) with a field that has default a
default value, but for which init=False.

- bpo-45803: Added missing kw_only parameter to
dataclasses.make_dataclass().

- bpo-45837: The :meth:`turtle.RawTurtle.settiltangle` is deprecated since
Python 3.1, it now emits a deprecation warning and will be removed in
Python 3.13.

Use :meth:`turtle.RawTurtle.tiltangle` instead.

:meth:`turtle.RawTurtle.tiltangle` was earlier incorrectly marked as
deprecated, its docstring has been corrected.

Patch by Hugo van Kemenade.

- bpo-45831: :mod:`faulthandler` can now write ASCII-only strings (like
filenames and function names) with a single write() syscall when dumping a
traceback. It reduces the risk of getting an unreadable dump when two
threads or two processes dump a traceback to the same file (like stderr)
at the same time. Patch by Victor Stinner.

- bpo-45828: :mod:`sqlite` C callbacks now use unraisable exceptions if
callback tracebacks are enabled. Patch by Erlend E. Aasland.

- bpo-41735: Fix thread lock in ``zlib.Decompress.flush()`` method before
``PyObject_GetBuffer``.

- bpo-45235: Reverted an argparse bugfix that caused regression in the
handling of default arguments for subparsers. This prevented leaf level
arguments from taking precedence over root level arguments.

- bpo-45754: Fix a regression in Python 3.11a1 and 3.11a2 where
:mod:`sqlite3` incorrectly would use ``SQLITE_LIMIT_LENGTH`` when checking
SQL statement lengths. Now, ``SQLITE_LIMIT_SQL_LENGTH`` is used. Patch by
Erlend E. Aasland.

- bpo-45766: Added *proportional* option to
:meth:`statistics.linear_regression`.

- bpo-45765: In importlib.metadata, fix distribution discovery for an empty
path.

- bpo-45757: Fix bug where :mod:`dis` produced an incorrect oparg when
:opcode:`EXTENDED_ARG` is followed by an opcode that does not use its
argument.

- bpo-45644: In-place JSON file formatting using ``python3 -m json.tool
infile infile`` now works correctly, previously it left the file empty.
Patch by Chris Wesseling.

- bpo-45703: When a namespace package is imported before another module from
the same namespace is created/installed in a different :data:`sys.path`
location while the program is running, calling the
:func:`importlib.invalidate_caches` function will now also guarantee the
new module is noticed.

- bpo-45535: Improve output of ``dir()`` with Enums.

- bpo-45664: Fix :func:`types.resolve_bases` and :func:`types.new_class` for
:class:`types.GenericAlias` instance as a base.

- bpo-45663: Fix :func:`dataclasses.is_dataclass` for dataclasses which are
subclasses of :class:`types.GenericAlias`.

- bpo-45662: Fix the repr of :data:`dataclasses.InitVar` with a type alias
to the built-in class, e.g. ``InitVar[list[int]]``.

- bpo-43137: Launch GNOME web browsers via gio tool instead of obsolete
gvfs-open

- bpo-45429: On Windows, :func:`time.sleep` now uses a waitable timer which
supports high-resolution timers. Patch by Dong-hee Na and Eryk Sun.

- bpo-37295: Optimize :func:`math.comb` and :func:`math.perm`.

- bpo-45514: Deprecated legacy functions in :mod:`importlib.resources`.

- bpo-45507: Add tests for truncated/missing trailers in gzip.decompress
implementation.

- bpo-45359: Implement :pep:`585` for :class:`graphlib.TopologicalSorter`.

- bpo-44733: Add ``max_tasks_per_child`` to
:class:`concurrent.futures.ProcessPoolExecutor`. This allows users to
specify the maximum number of tasks a single process should execute before
the process needs to be restarted.

- bpo-28806: Improve netrc library. netrc file no longer needs to contain
all tokens. And if the login name is anonymous, security check is no
longer need.

- bpo-43498: Avoid a possible *"RuntimeError: dictionary changed size during
iteration"* when adjusting the process count of
:class:`ProcessPoolExecutor`.

- bpo-42158: Add MIME types for N-quads, N-triples, Notation3 and TriG to
``mimetypes``.

- bpo-30533: Add :func:`inspect.getmembers_static` , it return all members
without triggering dynamic lookup via the descriptor protocol. Patch by
Weipeng Hong.

Documentation
-------------

- bpo-42238: ``make -C Doc suspicious`` will be removed soon in favor of
``make -C Doc check``, mark it as deprecated.

- bpo-45840: Improve cross-references in the documentation for the data
model.

- bpo-45640: Properly marked-up grammar tokens in the documentation are now
clickable and take you to the definition of a given piece of grammar.
Patch by Arthur Milchior.

- bpo-45788: Link doc for sys.prefix to sysconfig doc on installation paths.

- bpo-45772: ``socket.socket`` documentation is corrected to a class from a
function.

- bpo-45392: Update the docstring of the :class:`type` built-in to remove a
redundant line and to mention keyword arguments for the constructor.

- bpo-45250: Update the documentation to note that CPython does not
consistently require iterators to define ``__iter__``.

- bpo-25381: In the extending chapter of the extending doc, update a
paragraph about the global variables containing exception information.

- bpo-43905: Expanded :func:`~dataclasses.astuple` and
:func:`~dataclasses.asdict` docs, warning about deepcopy being applied and
providing a workaround.

Tests
-----

- bpo-45695: Out-of-tree builds with a read-only source directory are now
tested by CI.

- bpo-19460: Add new Test for
``Lib/email/mime/nonmultipart.py::MIMENonMultipart``.

- bpo-45835: Fix race condition in test_queue tests with multiple "feeder"
threads.

- bpo-45783: The test for the freeze tool now handles file moves and
deletions.

- bpo-45745: Remove the ``--findleaks`` command line option of regrtest: use
the ``--fail-env-changed`` option instead. Since Python 3.7, it was a
deprecated alias to the ``--fail-env-changed`` option.

- bpo-45701: Add tests with ``tuple`` type with :func:`functools.lru_cache`
to ``test_functools``.

Build
-----

- bpo-44035: CI now verifies that autoconf files have been regenerated with
a current and unpatched autoconf package.

- bpo-45950: The build system now uses a :program:`_bootstrap_python`
interpreter for freezing and deepfreezing again. To speed up build process
the build tools :program:`_bootstrap_python` and :program:`_freeze_module`
are no longer build with LTO.

- bpo-45881: The :program:`configure` script now accepts
``--with-build-python`` and ``--with-freeze-module`` options to make cross
compiling easier.

- bpo-40280: Emscripten platform now uses ``.wasm`` suffix by default.

- bpo-40280: Disable unusable core extension modules on WASM/Emscripten
targets.

- bpo-40280: ``configure`` now checks for socket ``shutdown`` function. The
check makes it possible to disable ``SYS_shutdown`` with
``ac_cv_func_shutdown=no`` in CONFIG_SITE.

- bpo-40280: ``configure`` now checks for functions ``fork1, getegid,
geteuid, getgid, getppid, getuid, opendir, pipe, system, wait, ttyname``.

- bpo-33393: Update ``config.guess`` to 2021-06-03 and ``config.sub`` to
2021-08-14. ``Makefile`` now has an ``update-config`` target to make
updating more convenient.

- bpo-45866: ``make regen-all`` now produces the same output when run from a
directory other than the source tree: when building Python out of the
source tree. pegen now strips directory of the "generated by pygen from
<FILENAME>" header Patch by Victor Stinner.

- bpo-40280: ``configure`` now accepts machine ``wasm32`` or ``wasm64`` and
OS ``wasi`` or ``emscripten`` for cross building, e.g.
``wasm32-unknown-emscripten``, ``wasm32-wasi``, or
``wasm32-unknown-wasi``.

- bpo-41498: Python now compiles on platforms without ``sigset_t``. Several
functions in :mod:`signal` are not available when ``sigset_t`` is missing.

Based on patch by Roman Yurchak for pyodide.

- bpo-45881: ``setup.py`` now uses ``CC`` from environment first to discover
multiarch and cross compile paths.

- bpo-45886: The ``_freeze_module`` program path can now be overridden on
the command line, e.g. ``make
FREEZE_MODULE=../x86_64/Program/_freeze_module``.

- bpo-45873: Get rid of the ``_bootstrap_python`` build step. The
deepfreeze.py script is now run using ``$(PYTHON_FOR_REGEN)`` which can be
Python 3.7 or newer (on Windows, 3.8 or newer).

- bpo-45847: Port builtin hashlib extensions to ``PY_STDLIB_MOD`` macro and
``addext()``.

- bpo-45723: Add ``autoconf`` helpers for saving and restoring environment
variables:

* ``SAVE_ENV``: Save ``$CFLAGS``, ``$LDFLAGS``, ``$LIBS``, and
``$CPPFLAGS``.
* ``RESTORE_ENV``: Restore ``$CFLAGS``, ``$LDFLAGS``, ``$LIBS``, and
``$CPPFLAGS``.
* ``WITH_SAVE_ENV([SCRIPT])``: Run ``SCRIPT`` wrapped with ``SAVE_ENV`` and
``RESTORE_ENV``.

Patch by Erlend E. Aasland.

- bpo-45573: Mandatory core modules, that are required to bootstrap Python,
are now in ``Modules/Setup.bootstrap``.

- bpo-45573: ``configure`` now creates ``Modules/Setup.stdlib`` with
conditionally enabled/disabled extension module lines. The file is not
used, yet.

- bpo-45573: ``configure`` now uses a unified format to set state, compiler
flags, and linker flags in Makefile. The new macro ``PY_STDLIB_MOD`` sets
three variables that are consumed by ``Modules/Setup`` and ``setup.py``.

- bpo-45816: Python now supports building with Visual Studio 2022 (MSVC
v143, VS Version 17.0). Patch by Jeremiah Vivian.

- bpo-45800: Settings for :mod:`pyexpat` C extension are now detected by
``configure``. The bundled ``expat`` library is built in ``Makefile``.

- bpo-45798: Settings for :mod:`decimal` internal C extension are now
detected by ``configure``. The bundled ``libmpdec`` library is built in
``Makefile``.

- bpo-45723: :program:`configure` has a new option ``--with-pkg-config`` to
disable or require pkg-config.

- bpo-45774: The build dependencies for :mod:`sqlite3` are now detected by
``configure`` and ``pkg-config``. Patch by Erlend E. Aasland.

- bpo-45763: The build dependencies for :mod:`zlib`, :mod:`bz2`, and
:mod:`lzma` are now detected by ``configure``.

- bpo-45747: gdbm and dbm build dependencies are now detected by
``configure``.

- bpo-45743: On macOS, the build system no longer passes
``search_paths_first`` to the linker. The flag has been the default since
Xcode 4 / macOS 10.6.

- bpo-45723: ``configure.ac`` is now compatible with autoconf 2.71.
Deprecated checks ``STDC_HEADERS`` and ``AC_HEADER_TIME`` have been
removed.

- bpo-45723: ``configure`` now prints a warning when pkg-config is missing.

- bpo-45731: ``configure --enable-loadable-sqlite-extensions`` is now
handled by new ``PY_SQLITE_ENABLE_LOAD_EXTENSION`` macro instead of logic
in setup.py.

- bpo-45723: configure.ac now uses custom helper macros and
``AC_CACHE_CHECK`` to simplify and speed up configure runs.

- bpo-45696: Skip the marshal step for frozen modules by generating C code
that produces a set of ready-to-use code objects. This speeds up startup
time by another 10% or more.

- bpo-45561: Run smelly.py tool from $(srcdir).

Windows
-------

- bpo-46105: Fixed calculation of :data:`sys.path` in a venv on Windows.

- bpo-45901: When installed through the Microsoft Store and set as the
default app for :file:`*.py` files, command line arguments will now be
passed to Python when invoking a script without explicitly launching
Python (that is, ``script.py args`` rather than ``python script.py
args``).

- bpo-45616: Fix Python Launcher's ability to distinguish between versions
3.1 and 3.10 when either one is explicitly requested. Previously, 3.1
would be used if 3.10 was requested but not installed, and 3.10 would be
used if 3.1 was requested but 3.10 was installed.

- bpo-45850: Implement changes to build with deep-frozen modules on Windows.
Note that we now require Python 3.10 as the "bootstrap" or "host" Python.

- bpo-45732: Updates bundled Tcl/Tk to 8.6.12.

- bpo-45720: Internal reference to :file:`shlwapi.dll` was dropped to help
improve startup time. This DLL will no longer be loaded at the start of
every Python process.

macOS
-----

- bpo-45732: Update python.org macOS installer to use Tcl/Tk 8.6.12.

C API
-----

- bpo-39026: Fix Python.h to build C extensions with Xcode: remove a
relative include from ``Include/cpython/pystate.h``.

What's New in Python 3.11.0 alpha 2?
====================================

*Release date: 2021-11-05*

Core and Builtins
-----------------

- bpo-45716: Improve the :exc:`SyntaxError` message when using ``True``,
``None`` or ``False`` as keywords in a function call. Patch by Pablo
Galindo.

- bpo-45688: :data:`sys.stdlib_module_names` now contains the macOS-specific
module :mod:`_scproxy`.

- bpo-45379: Clarify :exc:`ImportError` message when we try to explicitly
import a frozen module but frozen modules are disabled.

- bpo-44525: Specialize simple calls to Python functions (no starargs,
keyowrd dict, or closure)

- bpo-45530: Cases of sorting using tuples as keys may now be significantly
faster in some cases. Patch by Tim Peters.

The order of the result may differ from earlier releases if the tuple
elements don't define a total ordering (see
:ref:`expressions-value-comparisons` for information on total ordering).
It's generally true that the result of sorting simply isn't well-defined
in the absence of a total ordering on list elements.

- bpo-45526: In obmalloc, set ADDRESS_BITS to not ignore any bits (ignored
16 before). That is safer in the case that the kernel gives user-space
virtual addresses that span a range greater than 48 bits.

- bpo-30570: Fixed a crash in ``issubclass()`` from infinite recursion when
searching pathological ``__bases__`` tuples.

- bpo-45521: Fix a bug in the obmalloc radix tree code. On 64-bit machines,
the bug causes the tree to hold 46-bits of virtual addresses, rather than
the intended 48-bits.

- bpo-45494: Fix parser crash when reporting errors involving invalid
continuation characters. Patch by Pablo Galindo.

- bpo-45445: Python now fails to initialize if it finds an invalid
:option:`-X` option in the command line. Patch by Pablo Galindo.

- bpo-45340: Object attributes are held in an array instead of a dictionary.
An object's dictionary are created lazily, only when needed. Reduces the
memory consumption of a typical Python object by about 30%. Patch by Mark
Shannon.

- bpo-45408: Fix a crash in the parser when reporting tokenizer errors that
occur at the same time unclosed parentheses are detected. Patch by Pablo
Galindo.

- bpo-29410: Add SipHash13 for string hash algorithm and use it by default.

- bpo-45385: Fix reference leak from descr_check. Patch by Dong-hee Na.

- bpo-45367: Specialized the ``BINARY_MULTIPLY`` opcode to
``BINARY_MULTIPLY_INT`` and ``BINARY_MULTIPLY_FLOAT`` using the PEP 659
machinery.

- bpo-21736: Frozen stdlib modules now have ``__file__`` to the .py file
they would otherwise be loaded from, if possible. For packages,
``__path__`` now has the correct entry instead of being an empty list,
which allows unfrozen submodules to be imported. These are set only if
the stdlib directory is known when the runtime is initialized. Note that
the file at ``__file__`` is not guaranteed to exist. None of this affects
non-stdlib frozen modules nor, for now, frozen modules imported using
``PyImport_ImportFrozenModule()``. Also, at the moment ``co_filename`` is
not updated for the module.

- bpo-45020: For frozen stdlib modules, record the original module name as
``module.__spec__.loader_state.origname``. If the value is different than
``module.__spec__.name`` then the module was defined as an alias in
Tools/scripts/freeze_modules.py. If it is ``None`` then the module comes
from a source file outside the stdlib.

- bpo-45324: In FrozenImporter.find_spec(), we now preserve the information
needed in exec_module() to load the module. This change mostly impacts
internal details, rather than changing the importer's behavior.

- bpo-45292: Implement :pep:`654`. Add :class:`ExceptionGroup` and
:class:`BaseExceptionGroup`. Update traceback display code.

- bpo-40116: Change to the implementation of split dictionaries. Classes
where the instances differ either in the exact set of attributes, or in
the order in which those attributes are set, can still share keys. This
should have no observable effect on users of Python or the C-API. Patch by
Mark Shannon.

- bpo-44050: Extensions that indicate they use global state (by setting
``m_size`` to -1) can again be used in multiple interpreters. This reverts
to behavior of Python 3.8.

- bpo-44525: Setup initial specialization infrastructure for the
``CALL_FUNCTION`` opcode. Implemented initial specializations for C
function calls:

* ``CALL_FUNCTION_BUILTIN_O`` for ``METH_O`` flag.

* ``CALL_FUNCTION_BUILTIN_FAST`` for ``METH_FASTCALL`` flag without keywords.

* ``CALL_FUNCTION_LEN`` for ``len(o)``.

* ``CALL_FUNCTION_ISINSTANCE`` for ``isinstance(o, t)``.

- bpo-44511: Improve the generated bytecode for class and mapping patterns.

- bpo-43706: Speed up calls to ``enumerate()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

Library
-------

- bpo-45679: Fix caching of multi-value :data:`typing.Literal`.
``Literal[True, 2]`` is no longer equal to ``Literal[1, 2]``.

- bpo-42064: Convert :mod:`sqlite3` to multi-phase initialisation (PEP 489).
Patches by Erlend E. Aasland.

- bpo-45438: Fix typing.Signature string representation for generic builtin
types.

- bpo-45613: :mod:`sqlite3` now sets :attr:`sqlite3.threadsafety` based on
the default threading mode the underlying SQLite library has been compiled
with. Patch by Erlend E. Aasland.

- bpo-45574: Fix warning about ``print_escape`` being unused.

- bpo-45581: :meth:`sqlite3.connect` now correctly raises :exc:`MemoryError`
if the underlying SQLite API signals memory error. Patch by Erlend E.
Aasland.

- bpo-45557: pprint.pprint() now handles underscore_numbers correctly.
Previously it was always setting it to False.

- bpo-44019: Add :func:`operator.call` to ``operator.__all__``. Patch by
Kreusada.

- bpo-42174: :meth:`shutil.get_terminal_size` now falls back to sane values
if the column or line count are 0.

- bpo-35673: Improve the introspectability of the ``__loader__`` attribute
for namespace packages. :class:`importlib.machinery.NamespaceLoader` is
now public, and implements the :class:`importlib.abc.InspectLoader`
interface. ``_NamespaceLoader`` is kept for backward compatibility.

- bpo-45515: Add references to :mod:`zoneinfo` in the :mod:`datetime`
documentation, mostly replacing outdated references to ``dateutil.tz``.
Change by Paul Ganssle.

- bpo-45475: Reverted optimization of iterating :class:`gzip.GzipFile`,
:class:`bz2.BZ2File`, and :class:`lzma.LZMAFile` (see bpo-43787) because
it caused regression when user iterate them without having reference of
them. Patch by Inada Naoki.

- bpo-45489: Update :class:`~typing.ForwardRef` to support ``|`` operator.
Patch by Dong-hee Na.

- bpo-42222: Removed deprecated support for float arguments in
*randrange()*.

- bpo-45428: Fix a regression in py_compile when reading filenames from
standard input.

- bpo-45467: Fix incremental decoder and stream reader in the
"raw-unicode-escape" codec. Previously they failed if the escape sequence
was split.

- bpo-45461: Fix incremental decoder and stream reader in the
"unicode-escape" codec. Previously they failed if the escape sequence was
split.

- bpo-45239: Fixed :func:`email.utils.parsedate_tz` crashing with
:exc:`UnboundLocalError` on certain invalid input instead of returning
``None``. Patch by Ben Hoyt.

- bpo-45417: Fix quadratic behaviour in the enum module: Creation of enum
classes with a lot of entries was quadratic.

- bpo-45249: Fix the behaviour of :func:`traceback.print_exc` when
displaying the caret when the ``end_offset`` in the exception is set to 0.
Patch by Pablo Galindo

- bpo-45416: Fix use of :class:`asyncio.Condition` with explicit
:class:`asyncio.Lock` objects, which was a regression due to removal of
explicit loop arguments. Patch by Joongi Kim.

- bpo-20028: Empty escapechar/quotechar is not allowed when initializing
:class:`csv.Dialect`. Patch by Vajrasky Kok and Dong-hee Na.

- bpo-44904: Fix bug in the :mod:`doctest` module that caused it to fail if
a docstring included an example with a ``classmethod`` ``property``. Patch
by Alex Waygood.

- bpo-45406: Make :func:`inspect.getmodule` catch ``FileNotFoundError``
raised by :'func:`inspect.getabsfile`, and return ``None`` to indicate
that the module could not be determined.

- bpo-45411: Add extensions for files containing subtitles - .srt & .vtt -
to the mimetypes.py module.

- bpo-10716: Migrated pydoc to HTML5 (without changing the look of it). Side
effect is to update xmlrpc's ``ServerHTMLDoc`` which now uses the CSS too.
cgitb now relies less on pydoc (as it can't use the CSS file).

- bpo-27580: Add support of null characters in :mod:`csv`.

- bpo-45262: Prevent use-after-free in asyncio. Make sure the cached running
loop holder gets cleared on dealloc to prevent use-after-free in
get_running_loop

- bpo-45386: Make :mod:`xmlrpc.client` more robust to C runtimes where the
underlying C ``strftime`` function results in a ``ValueError`` when
testing for year formatting options.

- bpo-20028: Improve error message of :class:`csv.Dialect` when
initializing. Patch by Vajrasky Kok and Dong-hee Na.

- bpo-45343: Update bundled pip to 21.2.4 and setuptools to 58.1.0

- bpo-45328: Fixed :class:`http.client.HTTPConnection` to work properly in
OSs that don't support the ``TCP_NODELAY`` socket option.

- bpo-45243: Add :meth:`~sqlite3.Connection.setlimit` and
:meth:`~sqlite3.Connection.getlimit` to :class:`sqlite3.Connection` for
setting and getting SQLite limits by connection basis. Patch by Erlend E.
Aasland.

- bpo-45320: Removed from the :mod:`inspect` module:

* the ``getargspec`` function, deprecated since Python 3.0;
use :func:`inspect.signature` or :func:`inspect.getfullargspec` instead.

* the ``formatargspec`` function, deprecated since Python 3.5;
use the :func:`inspect.signature` function and :class:`Signature` object
directly.

* the undocumented ``Signature.from_callable`` and ``Signature.from_function``
functions, deprecated since Python 3.5; use the
:meth:`Signature.from_callable() <inspect.Signature.from_callable>` method
instead.

Patch by Hugo van Kemenade.

- bpo-45192: Fix the ``tempfile._infer_return_type`` function so that the
``dir`` argument of the :mod:`tempfile` functions accepts an object
implementing the ``os.PathLike`` protocol.

Patch by Kyungmin Lee.

- bpo-45160: When tracing a tkinter variable used by a ttk OptionMenu,
callbacks are no longer made twice.

- bpo-25625: Added non parallel-safe :func:`~contextlib.chdir` context
manager to change the current working directory and then restore it on
exit. Simple wrapper around :func:`~os.chdir`.

- bpo-24139: Add support for SQLite extended result codes in
:exc:`sqlite3.Error`. Patch by Erlend E. Aasland.

- bpo-24444: Fixed an error raised in :mod:`argparse` help display when help
for an option is set to 1+ blank spaces or when *choices* arg is an empty
container.

- bpo-44547: Implement ``Fraction.__int__``, so that a
:class:`fractions.Fraction` instance ``f`` passes an ``isinstance(f,
typing.SupportsInt)`` check.

- bpo-40321: Adds support for HTTP 308 redirects to :mod:`urllib`. See
:rfc:`7538` for details. Patch by Jochem Schulenklopper.

- bpo-41374: Ensure that ``socket.TCP_*`` constants are exposed on Cygwin
3.1.6 and greater.

- bpo-35970: Add help flag to the base64 module's command line interface.
Patch contributed by Robert Kuska.

Documentation
-------------

- bpo-45726: Improve documentation for :func:`functools.singledispatch` and
:class:`functools.singledispatchmethod`.

- bpo-45680: Amend the docs on ``GenericAlias`` objects to clarify that
non-container classes can also implement ``__class_getitem__``. Patch
contributed by Alex Waygood.

- bpo-45618: Update Sphinx version used to build the documentation to 4.2.0.
Patch by Maciej Olko.

- bpo-45655: Add a new "relevant PEPs" section to the top of the
documentation for the ``typing`` module. Patch by Alex Waygood.

- bpo-45604: Add ``level`` argument to ``multiprocessing.log_to_stderr``
function docs.

- bpo-45516: Add protocol description to the
:class:`importlib.abc.TraversableResources` documentation.

- bpo-45464: Mention in the documentation of :ref:`Built-in Exceptions
<bltin-exceptions>` that inheriting from multiple exception types in a
single subclass is not recommended due to possible memory layout
incompatibility.

- bpo-45449: Add note about :pep:`585` in :mod:`collections.abc`.

- bpo-45516: Add protocol description to the
:class:`importlib.abc.Traversable` documentation.

- bpo-20692: Add Programming FAQ entry explaining that int literal attribute
access requires either a space after or parentheses around the literal.

Tests
-----

- bpo-45678: Add tests for scenarios in which
:class:`functools.singledispatchmethod` is stacked on top of a method that
has already been wrapped by two other decorators. Patch by Alex Waygood.

- bpo-45578: Add tests for :func:`dis.distb`

- bpo-45678: Add tests to ensure that ``functools.singledispatchmethod``
correctly wraps the attributes of the target function.

- bpo-45668: PGO tests now pass when Python is built without test extension
modules.

- bpo-45577: Add subtests for all ``pickle`` protocols in ``test_zoneinfo``.

- bpo-45566: Fix ``test_frozen_pickle`` in ``test_dataclasses`` to check all
``pickle`` versions.

- bpo-43592: :mod:`test.libregrtest` now raises the soft resource limit for
the maximum number of file descriptors when the default is too low for our
test suite as was often the case on macOS.

- bpo-39679: Add more test cases for `@functools.singledispatchmethod` when
combined with `@classmethod` or `@staticmethod`.

- bpo-45410: When libregrtest spawns a worker process, stderr is now written
into stdout to keep messages order. Use a single pipe for stdout and
stderr, rather than two pipes. Previously, messages were out of order
which made analysis of buildbot logs harder Patch by Victor Stinner.

- bpo-45402: Fix test_tools.test_sundry() when Python is built out of tree:
fix how the freeze_modules.py tool locates the _freeze_module program.
Patch by Victor Stinner.

- bpo-45403: Fix test_sys.test_stdlib_dir() when Python is built outside the
source tree: compare normalized paths. Patch by Victor Stinner.

- bpo-45400: Fix
test_name_error_suggestions_do_not_trigger_for_too_many_locals() of
test_exceptions if a directory name contains "a1" (like
"Python-3.11.0a1"): use a stricter regular expression. Patch by Victor
Stinner.

- bpo-10572: Rename :mod:`sqlite3` tests from ``test_sqlite`` to
``test_sqlite3``, and relocate them to ``Lib/test/test_sqlite3``. Patch by
Erlend E. Aasland.

Build
-----

- bpo-43158: ``setup.py`` now uses values from configure script to build the
``_uuid`` extension module. Configure now detects util-linux's
``libuuid``, too.

- bpo-45666: Fix warning of ``swprintf`` and ``%s`` usage in
``_testembed.c``

- bpo-45548: ``Modules/Setup`` and ``Modules/makesetup`` have been improved.
The ``Setup`` file now contains working rules for all extensions. Outdated
comments have been removed. Rules defined by ``makesetup`` track
dependencies correctly.

- bpo-45548: The :mod:`math` and :mod:`cmath` implementation now require a
C99 compatible ``libm`` and no longer ship with workarounds for missing
acosh, asinh, atanh, expm1, and log1p functions.

- bpo-45595: ``setup.py`` and ``makesetup`` now track build dependencies on
all Python header files and module specific header files.

- bpo-45571: ``Modules/Setup`` now use ``PY_CFLAGS_NODIST`` instead of
``PY_CFLAGS`` to compile shared modules.

- bpo-45570: :mod:`pyexpat` and :mod:`_elementtree` no longer define
obsolete macros ``HAVE_EXPAT_CONFIG_H`` and ``USE_PYEXPAT_CAPI``.
``XML_POOR_ENTROPY`` is now defined in ``expat_config.h``.

- bpo-43974: ``setup.py`` no longer defines ``Py_BUILD_CORE_MODULE``.
Instead every module, that uses the internal API, defines the macro.

- bpo-45548: Fill in missing entries in Modules/Setup.

- bpo-45532: Update :data:`sys.version` to use ``main`` as fallback
information. Patch by Jeong YunWon.

- bpo-45536: The ``configure`` script now checks whether OpenSSL headers and
libraries provide required APIs. Most common APIs are verified. The check
detects outdated or missing OpenSSL. Failures do not stop configure.

- bpo-45221: Fixed regression in handling of ``LDFLAGS`` and ``CPPFLAGS``
options where :meth:`argparse.parse_known_args` could interpret an option
as one of the built-in command line argument, for example ``-h`` for help.

- bpo-45440: Building Python now requires a C99 ``<math.h>`` header file
providing the following functions: ``copysign()``, ``hypot()``,
``isfinite()``, ``isinf()``, ``isnan()``, ``round()``. Patch by Victor
Stinner.

- bpo-45405: Prevent ``internal configure error`` when running ``configure``
with recent versions of non-Apple clang. Patch by David Bohman.

- bpo-45433: Avoid linking libpython with libcrypt.

Windows
-------

- bpo-43652: Update Tcl/Tk to 8.6.11, actually this time. The previous
update incorrectly included 8.6.10.

- bpo-45337: venv now warns when the created environment may need to be
accessed at a different path, due to redirections, links or junctions. It
also now correctly installs or upgrades components when the alternate path
is required.

- bpo-43851: Build SQLite ``SQLITE_OMIT_AUTOINIT`` on Windows. Patch by
Erlend E. Aasland.

macOS
-----

- bpo-44828: Avoid tkinter file dialog failure on macOS 12 Monterey when
using the Tk 8.6.11 provided by python.org macOS installers. Patch by Marc
Culler of the Tk project.

IDLE
----

- bpo-45495: Add context keywords 'case' and 'match' to completions list.

C API
-----

- bpo-29103: :c:func:`PyType_FromSpec* <PyType_FromModuleAndSpec>` now
copies the class name from the spec to a buffer owned by the class, so the
original can be safely deallocated. Patch by Petr Viktorin.

- bpo-45522: The internal freelists for frame, float, list, dict, async
generators, and context objects can now be disabled.

- bpo-35134: Exclude :c:func:`PyWeakref_GET_OBJECT` from the limited C API.
It never worked since the :c:type:`PyWeakReference` structure is opaque in
the limited C API.

- bpo-35081: Move the ``interpreteridobject.h`` header file from
``Include/`` to ``Include/internal/``. It only provides private functions.
Patch by Victor Stinner.

- bpo-35134: The non-limited API files ``cellobject.h``, ``classobject.h``,
``context.h``, ``funcobject.h``, ``genobject.h`` and ``longintrepr.h``
have been moved to the ``Include/cpython`` directory. Moreover, the
``eval.h`` header file was removed. These files must not be included
directly, as they are already included in ``Python.h``: :ref:`Include
Files <api-includes>`. If they have been included directly, consider
including ``Python.h`` instead. Patch by Victor Stinner.

- bpo-45474: The following items are no longer available when
``Py_LIMITED_API`` is defined:

* :c:func:`PyMarshal_WriteLongToFile`
* :c:func:`PyMarshal_WriteObjectToFile`
* :c:func:`PyMarshal_ReadObjectFromString`
* :c:func:`PyMarshal_WriteObjectToString`
* the ``Py_MARSHAL_VERSION`` macro

These are not part of the :ref:`limited API <stable-abi-list>`.

Patch by Victor Stinner.

- bpo-45434: Remove the ``pystrhex.h`` header file. It only contains private
functions. C extensions should only include the main ``<Python.h>`` header
file. Patch by Victor Stinner.

- bpo-45440: Remove the ``Py_FORCE_DOUBLE()`` macro. It was used by the
``Py_IS_INFINITY()`` macro. Patch by Victor Stinner.

- bpo-45434: ``<Python.h>`` no longer includes the header files
``<stdlib.h>``, ``<stdio.h>``, ``<errno.h>`` and ``<string.h>`` when the
``Py_LIMITED_API`` macro is set to ``0x030b0000`` (Python 3.11) or higher.
C extensions should explicitly include the header files after ``#include
<Python.h>``. Patch by Victor Stinner.

- bpo-41123: Remove ``Py_UNICODE_COPY()`` and ``Py_UNICODE_FILL()`` macros,
deprecated since Python 3.3. Use ``PyUnicode_CopyCharacters()`` or
``memcpy()`` (``wchar_t*`` string), and ``PyUnicode_Fill()`` functions
instead. Patch by Victor Stinner.

- bpo-45412: Remove the following math macros using the ``errno`` variable:

* ``Py_ADJUST_ERANGE1()``
* ``Py_ADJUST_ERANGE2()``
* ``Py_OVERFLOWED()``
* ``Py_SET_ERANGE_IF_OVERFLOW()``
* ``Py_SET_ERRNO_ON_MATH_ERROR()``

Patch by Victor Stinner.

- bpo-45395: Custom frozen modules (the array set to
``PyImport_FrozenModules``) are now treated as additions, rather than
replacing all the default frozen modules. Frozen stdlib modules can still
be disabled by setting the "code" field of the custom array entry to NULL.

- bpo-43760: Add new :c:func:`PyThreadState_EnterTracing`, and
:c:func:`PyThreadState_LeaveTracing` functions to the limited C API to
suspend and resume tracing and profiling. Patch by Victor Stinner.

- bpo-44220: :c:var:`PyStructSequence_UnnamedField` is added to the Stable
ABI.

What's New in Python 3.11.0 alpha 1?
====================================

*Release date: 2021-10-05*

Security
--------

- bpo-42278: Replaced usage of :func:`tempfile.mktemp` with
:class:`~tempfile.TemporaryDirectory` to avoid a potential race condition.

- bpo-44600: Fix incorrect line numbers while tracing some failed patterns
in :ref:`match <match>` statements. Patch by Charles Burkland.

- bpo-41180: Add auditing events to the :mod:`marshal` module, and stop
raising ``code.__init__`` events for every unmarshalled code object.
Directly instantiated code objects will continue to raise an event, and
audit event handlers should inspect or collect the raw marshal data. This
reduces a significant performance overhead when loading from ``.pyc``
files.

- bpo-44394: Update the vendored copy of libexpat to 2.4.1 (from 2.2.8) to
get the fix for the CVE-2013-0340 "Billion Laughs" vulnerability. This
copy is most used on Windows and macOS.

- bpo-43124: Made the internal ``putcmd`` function in :mod:`smtplib`
sanitize input for presence of ``\r`` and ``\n`` characters to avoid
(unlikely) command injection.

- bpo-44022: :mod:`http.client` now avoids infinitely reading potential HTTP
headers after a ``100 Continue`` status response from the server.

Core and Builtins
-----------------

- bpo-43760: The number of hardware branches per instruction dispatch is
reduced from two to one by adding a special instruction for tracing. Patch
by Mark Shannon.

- bpo-45061: Add a deallocator to the bool type to detect refcount bugs in C
extensions which call Py_DECREF(Py_True) or Py_DECREF(Py_False) by
mistake. Detect also refcount bugs when the empty tuple singleton or the
Unicode empty string singleton is destroyed by mistake. Patch by Victor
Stinner.

- bpo-24076: sum() was further optimised for summing up single digit
integers.

- bpo-45190: Update Unicode databases to Unicode 14.0.0.

- bpo-45167: Fix deepcopying of :class:`types.GenericAlias` objects.

- bpo-45155: :meth:`int.to_bytes` and :meth:`int.from_bytes` now take a
default value of ``"big"`` for the ``byteorder`` argument.
:meth:`int.to_bytes` also takes a default value of ``1`` for the
``length`` argument.

- bpo-44219: Release the GIL while performing ``isatty`` system calls on
arbitrary file descriptors. In particular, this affects :func:`os.isatty`,
:func:`os.device_encoding` and :class:`io.TextIOWrapper`. By extension,
:func:`io.open` in text mode is also affected. This change solves a
deadlock in :func:`os.isatty`. Patch by Vincent Michel in :issue:`44219`.

- bpo-44959: Added fallback to extension modules with '.sl' suffix on HP-UX

- bpo-45121: Fix issue where ``Protocol.__init__`` raises ``RecursionError``
when it's called directly or via ``super()``. Patch provided by Yurii
Karabas.

- bpo-44348: The deallocator function of the :exc:`BaseException` type now
uses the trashcan mechanism to prevent stack overflow. For example, when a
:exc:`RecursionError` instance is raised, it can be linked to another
RecursionError through the ``__context__`` attribute or the
``__traceback__`` attribute, and then a chain of exceptions is created.
When the chain is destroyed, nested deallocator function calls can crash
with a stack overflow if the chain is too long compared to the available
stack memory. Patch by Victor Stinner.

- bpo-45123: Fix PyAiter_Check to only check for the __anext__ presence (not
for __aiter__). Rename PyAiter_Check to PyAIter_Check, PyObject_GetAiter
-> PyObject_GetAIter.

- bpo-1514420: Interpreter no longer attempts to open files with names in
angle brackets (like "<string>" or "<stdin>") when formatting an
exception.

- bpo-41031: Match C and Python code formatting of unprintable exceptions
and exceptions in the :mod:`__main__` module.

- bpo-37330: :func:`open`, :func:`io.open`, :func:`codecs.open` and
:class:`fileinput.FileInput` no longer accept ``'U'`` ("universal
newline") in the file mode. This flag was deprecated since Python 3.3.
Patch by Victor Stinner.

- bpo-45083: When the interpreter renders an exception, its name now has a
complete qualname. Previously only the class name was concatenated to the
module name, which sometimes resulted in an incorrect full name being
displayed.

(This issue impacted only the C code exception rendering, the
:mod:`traceback` module was using qualname already).

- bpo-34561: List sorting now uses the merge-ordering strategy from Munro
and Wild's ``powersort()``. Unlike the former strategy, this is provably
near-optimal in the entropy of the distribution of run lengths. Most uses
of ``list.sort()`` probably won't see a significant time difference, but
may see significant improvements in cases where the former strategy was
exceptionally poor. However, as these are all fast linear-time
approximations to a problem that's inherently at best quadratic-time to
solve truly optimally, it's also possible to contrive cases where the
former strategy did better.

- bpo-45056: Compiler now removes trailing unused constants from co_consts.

- bpo-45020: Add a new command line option, "-X frozen_modules=[on|off]" to
opt out of (or into) using optional frozen modules. This defaults to "on"
(or "off" if it's running out of the source tree).

- bpo-45012: In :mod:`posix`, release GIL during ``stat()``, ``lstat()``,
and ``fstatat()`` syscalls made by :func:`os.DirEntry.stat`. Patch by
Stanisław Skonieczny.

- bpo-45018: Fixed pickling of range iterators that iterated for over
``2**32`` times.

- bpo-45000: A :exc:`SyntaxError` is now raised when trying to delete
:const:`__debug__`. Patch by Dong-hee Na.

- bpo-44963: Implement ``send()`` and ``throw()`` methods for
``anext_awaitable`` objects. Patch by Pablo Galindo.

- bpo-44962: Fix a race in WeakKeyDictionary, WeakValueDictionary and
WeakSet when two threads attempt to commit the last pending removal. This
fixes asyncio.create_task and fixes a data loss in asyncio.run where
shutdown_asyncgens is not run

- bpo-24234: Implement the :meth:`__bytes__` special method on the
:class:`bytes` type, so a bytes object ``b`` passes an ``isinstance(b,
typing.SupportsBytes)`` check.

- bpo-24234: Implement the :meth:`__complex__` special method on the
:class:`complex` type, so a complex number ``z`` passes an ``isinstance(z,
typing.SupportsComplex)`` check.

- bpo-44954: Fixed a corner case bug where the result of
``float.fromhex('0x.8p-1074')`` was rounded the wrong way.

- bpo-44947: Refine the syntax error for trailing commas in import
statements. Patch by Pablo Galindo.

- bpo-44945: Specialize the BINARY_ADD instruction using the PEP 659
machinery. Adds five new instructions:

* BINARY_ADD_ADAPTIVE
* BINARY_ADD_FLOAT
* BINARY_ADD_INT
* BINARY_ADD_UNICODE
* BINARY_ADD_UNICODE_INPLACE_FAST

- bpo-44929: Fix some edge cases of ``enum.Flag`` string representation in
the REPL. Patch by Pablo Galindo.

- bpo-44914: Class version tags are no longer recycled.

This means that a version tag serves as a unique identifier for the state
of a class. We rely on this for effective specialization of the LOAD_ATTR
and other instructions.

- bpo-44698: Restore behaviour of complex exponentiation with integer-valued
exponent of type :class:`float` or :class:`complex`.

- bpo-44895: A debug variable :envvar:`PYTHONDUMPREFSFILE` is added for
creating a dump file which is generated by :option:`--with-trace-refs`.
Patch by Dong-hee Na.

- bpo-44900: Add five superinstructions for PEP 659 quickening:

* LOAD_FAST LOAD_FAST
* STORE_FAST LOAD_FAST
* LOAD_FAST LOAD_CONST
* LOAD_CONST LOAD_FAST
* STORE_FAST STORE_FAST

- bpo-44889: Initial implementation of adaptive specialization of
``LOAD_METHOD``. The following specialized forms were added:

* ``LOAD_METHOD_CACHED``

* ``LOAD_METHOD_MODULE``

* ``LOAD_METHOD_CLASS``

- bpo-44890: Specialization stats are always collected in debug builds.

- bpo-44885: Correct the ast locations of f-strings with format specs and
repeated expressions. Patch by Pablo Galindo

- bpo-44878: Remove the loop from the bytecode interpreter. All instructions
end with a DISPATCH macro, so the loop is now redundant.

- bpo-44878: Remove switch statement for interpreter loop when using
computed gotos. This makes sure that we only have one dispatch table in
the interpreter.

- bpo-44874: Deprecate the old trashcan macros
(``Py_TRASHCAN_SAFE_BEGIN``/``Py_TRASHCAN_SAFE_END``). They should be
replaced by the new macros ``Py_TRASHCAN_BEGIN`` and ``Py_TRASHCAN_END``.

- bpo-44872: Use new trashcan macros (Py_TRASHCAN_BEGIN/END) in
frameobject.c instead of the old ones (Py_TRASHCAN_SAFE_BEGIN/END).

- bpo-33930: Fix segmentation fault with deep recursion when cleaning method
objects. Patch by Augusto Goulart and Pablo Galindo.

- bpo-25782: Fix bug where ``PyErr_SetObject`` hangs when the current
exception has a cycle in its context chain.

- bpo-44856: Fix reference leaks in the error paths of ``update_bases()``
and ``__build_class__``. Patch by Pablo Galindo.

- bpo-44826: Initial implementation of adaptive specialization of STORE_ATTR

Three specialized forms of STORE_ATTR are added:

* STORE_ATTR_SLOT

* STORE_ATTR_SPLIT_KEYS

* STORE_ATTR_WITH_HINT

- bpo-44838: Fixed a bug that was causing the parser to raise an incorrect
custom :exc:`SyntaxError` for invalid 'if' expressions. Patch by Pablo
Galindo.

- bpo-44821: Create instance dictionaries (__dict__) eagerly, to improve
regularity of object layout and assist specialization.

- bpo-44792: Improve syntax errors for if expressions. Patch by Miguel Brito

- bpo-34013: Generalize the invalid legacy statement custom error message
(like the one generated when "print" is called without parentheses) to
include more generic expressions. Patch by Pablo Galindo

- bpo-44732: Rename ``types.Union`` to ``types.UnionType``.

- bpo-44725: Expose specialization stats in python via
:func:`_opcode.get_specialization_stats`.

- bpo-44717: Improve AttributeError on circular imports of submodules.

- bpo-44698: Fix undefined behaviour in complex object exponentiation.

- bpo-44653: Support :mod:`typing` types in parameter substitution in the
union type.

- bpo-44676: Add ability to serialise ``types.Union`` objects. Patch
provided by Yurii Karabas.

- bpo-44633: Parameter substitution of the union type with wrong types now
raises ``TypeError`` instead of returning ``NotImplemented``.

- bpo-44661: Update ``property_descr_set`` to use vectorcall if possible.
Patch by Dong-hee Na.

- bpo-44662: Add ``__module__`` to ``types.Union``. This also fixes
``types.Union`` issues with ``typing.Annotated``. Patch provided by Yurii
Karabas.

- bpo-44655: Include the name of the type in unset __slots__ attribute
errors. Patch by Pablo Galindo

- bpo-44655: Don't include a missing attribute with the same name as the
failing one when offering suggestions for missing attributes. Patch by
Pablo Galindo

- bpo-44646: Fix the hash of the union type: it no longer depends on the
order of arguments.

- bpo-44636: Collapse union of equal types. E.g. the result of ``int | int``
is now ``int``. Fix comparison of the union type with non-hashable
objects. E.g. ``int | str == {}`` no longer raises a TypeError.

- bpo-44611: On Windows, :func:`os.urandom`: uses BCryptGenRandom API
instead of CryptGenRandom API which is deprecated from Microsoft Windows
API. Patch by Dong-hee Na.

- bpo-44635: Convert ``None`` to ``type(None)`` in the union type
constructor.

- bpo-26280: Implement adaptive specialization for BINARY_SUBSCR

Three specialized forms of BINARY_SUBSCR are added:

* BINARY_SUBSCR_LIST_INT

* BINARY_SUBSCR_TUPLE_INT

* BINARY_SUBSCR_DICT

- bpo-44589: Mapping patterns in ``match`` statements with two or more equal
literal keys will now raise a :exc:`SyntaxError` at compile-time.

- bpo-44606: Fix ``__instancecheck__`` and ``__subclasscheck__`` for the
union type.

- bpo-42073: The ``@classmethod`` decorator can now wrap other
classmethod-like descriptors.

- bpo-41972: Tuned the string-searching algorithm of fastsearch.h to have a
shorter inner loop for most cases.

- bpo-44590: All necessary data for executing a Python function (local
variables, stack, etc) is now kept in a per-thread stack. Frame objects
are lazily allocated on demand. This increases performance by about 7% on
the standard benchmark suite. Introspection and debugging are unaffected
as frame objects are always available when needed. Patch by Mark Shannon.

- bpo-44584: The threading debug (:envvar:`PYTHONTHREADDEBUG` environment
variable) is deprecated in Python 3.10 and will be removed in Python 3.12.
This feature requires a debug build of Python. Patch by Victor Stinner.

- bpo-43895: An obsolete internal cache of shared object file handles added
in 1995 that attempted, but did not guarantee, that a .so would not be
dlopen'ed twice to work around flaws in mid-1990s posix-ish operating
systems has been removed from dynload_shlib.c.

- bpo-44490: :mod:`typing` now searches for type parameters in
``types.Union`` objects. ``get_type_hints`` will also properly resolve
annotations with nested ``types.Union`` objects. Patch provided by Yurii
Karabas.

- bpo-43950: Code objects can now provide the column information for
instructions when available. This is levaraged during traceback printing
to show the expressions responsible for errors.

Contributed by Pablo Galindo, Batuhan Taskaya and Ammar Askar as part of
:pep:`657`.

- bpo-44562: Remove uses of :c:func:`PyObject_GC_Del` in error path when
initializing :class:`types.GenericAlias`.

- bpo-41486: Fix a memory consumption and copying performance regression in
earlier 3.10 beta releases if someone used an output buffer larger than
4GiB with zlib.decompress on input data that expands that large.

- bpo-43908: Heap types with the :const:`Py_TPFLAGS_IMMUTABLETYPE` flag can
now inherit the :pep:`590` vectorcall protocol. Previously, this was only
possible for :ref:`static types <static-types>`. Patch by Erlend E.
Aasland.

- bpo-44553: Implement GC methods for ``types.Union`` to break reference
cycles and prevent memory leaks.

- bpo-44490: Add ``__parameters__`` attribute and ``__getitem__`` operator
to ``types.Union``. Patch provided by Yurii Karabas.

- bpo-44523: Remove the pass-through for :func:`hash` of
:class:`weakref.proxy` objects to prevent unintended consequences when the
original referred object dies while the proxy is part of a hashable
object. Patch by Pablo Galindo.

- bpo-44483: Fix a crash in ``types.Union`` objects when creating a union of
an object with bad ``__module__`` field.

- bpo-44486: Modules will always have a dictionary, even when created by
``types.ModuleType.__new__()``

- bpo-44472: Fix ltrace functionality when exceptions are raised. Patch by
Pablo Galindo

- bpo-12022: A :exc:`TypeError` is now raised instead of an
:exc:`AttributeError` in :keyword:`with` and :keyword:`async with`
statements for objects which do not support the :term:`context manager` or
:term:`asynchronous context manager` protocols correspondingly.

- bpo-44297: Make sure that the line number is set when entering a
comprehension scope. Ensures that backtraces inclusing generator
expressions show the correct line number.

- bpo-44456: Improve the syntax error when mixing positional and keyword
patterns. Patch by Pablo Galindo.

- bpo-44409: Fix error location information for tokenizer errors raised on
initialization of the tokenizer. Patch by Pablo Galindo.

- bpo-44396: Fix a possible crash in the tokenizer when raising syntax
errors for unclosed strings. Patch by Pablo Galindo.

- bpo-44376: Exact integer exponentiation (like ``i**2`` or ``pow(i, 2)``)
with a small exponent is much faster, due to reducing overhead in such
cases.

- bpo-44313: Directly imported objects and modules (through import and from
import statements) don't generate ``LOAD_METHOD``/``CALL_METHOD`` for
directly accessed objects on their namespace. They now use the regular
``LOAD_ATTR``/``CALL_FUNCTION``.

- bpo-44338: Implement adaptive specialization for LOAD_GLOBAL

Two specialized forms of LOAD_GLOBAL are added:

* LOAD_GLOBAL_MODULE

* LOAD_GLOBAL_BUILTIN

- bpo-44368: Improve syntax errors for invalid "as" targets. Patch by Pablo
Galindo

- bpo-44349: Fix an edge case when displaying text from files with encoding
in syntax errors. Patch by Pablo Galindo.

- bpo-44337: Initial implementation of adaptive specialization of LOAD_ATTR

Four specialized forms of LOAD_ATTR are added:

* LOAD_ATTR_SLOT

* LOAD_ATTR_SPLIT_KEYS

* LOAD_ATTR_WITH_HINT

* LOAD_ATTR_MODULE

- bpo-44335: Fix a regression when identifying incorrect characters in
syntax errors. Patch by Pablo Galindo

- bpo-43693: Computation of the offsets of cell variables is done in the
compiler instead of at runtime. This reduces the overhead of handling cell
and free variables, especially in the case where a variable is both an
argument and cell variable.

- bpo-44317: Improve tokenizer error with improved locations. Patch by Pablo
Galindo.

- bpo-44304: Fix a crash in the :mod:`sqlite3` module that happened when the
garbage collector clears :class:`sqlite.Statement` objects. Patch by Pablo
Galindo

- bpo-44305: Improve error message for ``try`` blocks without ``except`` or
``finally`` blocks. Patch by Pablo Galindo.

- bpo-43413: Constructors of subclasses of some builtin classes (e.g.
:class:`tuple`, :class:`list`, :class:`frozenset`) no longer accept
arbitrary keyword arguments. [reverted in 3.11a4] Subclass of :class:`set`
can now define a ``__new__()`` method with additional keyword parameters
without overriding also ``__init__()``.

- bpo-43667: Improve Unicode support in non-UTF locales on Oracle Solaris.
This issue does not affect other Solaris systems.

- bpo-43693: A new opcode MAKE_CELL has been added that effectively moves
some of the work done on function entry into the compiler and into the
eval loop. In addition to creating the required cell objects, the new
opcode converts relevant arguments (and other locals) to cell variables on
function entry.

- bpo-44232: Fix a regression in :func:`type` when a metaclass raises an
exception. The C function :c:func:`type_new` must properly report the
exception when a metaclass constructor raises an exception and the winner
class is not the metaclass. Patch by Victor Stinner.

- bpo-44201: Avoid side effects of checking for specialized syntax errors in
the REPL that was causing it to ask for extra tokens after a syntax error
had been detected. Patch by Pablo Galindo

- bpo-43693: ``PyCodeObject`` gained ``co_fastlocalnames`` and
``co_fastlocalkinds`` as the authoritative source of fast locals info.
Marshaled code objects have changed accordingly.

- bpo-44184: Fix a crash at Python exit when a deallocator function removes
the last strong reference to a heap type. Patch by Victor Stinner.

- bpo-44187: Implement quickening in the interpreter. This offers no
advantages as yet, but is an enabler of future optimizations. See PEP 659
for full explanation.

- bpo-44180: The parser doesn't report generic syntax errors that happen in
a position further away that the one it reached in the first pass. Patch
by Pablo Galindo

- bpo-44168: Fix error message in the parser involving keyword arguments
with invalid expressions. Patch by Pablo Galindo

- bpo-44156: String caches in ``compile.c`` are now subinterpreter
compatible.

- bpo-44143: Fixed a crash in the parser that manifest when raising
tokenizer errors when an existing exception was present. Patch by Pablo
Galindo.

- bpo-44032: Move 'fast' locals and other variables from the frame object to
a per-thread datastack.

- bpo-44114: Fix incorrect dictkeys_reversed and dictitems_reversed function
signatures in C code, which broke webassembly builds.

- bpo-44110: Improve :func:`str.__getitem__` error message

- bpo-26110: Add ``CALL_METHOD_KW`` opcode to speed up method calls with
keyword arguments. Idea originated from PyPy. A side effect is executing
``CALL_METHOD`` is now branchless in the evaluation loop.

- bpo-28307: Compiler now optimizes simple C-style formatting with literal
format containing only format codes %s, %r and %a by converting them to
f-string expressions.

- bpo-43149: Correct the syntax error message regarding multiple exception
types to not refer to "exception groups". Patch by Pablo Galindo

- bpo-43822: The parser will prioritize tokenizer errors over custom syntax
errors when raising exceptions. Patch by Pablo Galindo.

- bpo-40222: "Zero cost" exception handling.

* Uses a lookup table to determine how to handle exceptions.
* Removes SETUP_FINALLY and POP_TOP block instructions, eliminating the runtime overhead of try statements.
* Reduces the size of the frame object by about 60%.

Patch by Mark Shannon

- bpo-43918: Document the signature and ``default`` argument in the
docstring of the new ``anext`` builtin.

- bpo-43833: Emit a deprecation warning if the numeric literal is
immediately followed by one of keywords: and, else, for, if, in, is, or.
Raise a syntax error with more informative message if it is immediately
followed by other keyword or identifier.

- bpo-43879: Add native_thread_id to PyThreadState. Patch by Gabriele N.
Tornetta.

- bpo-43693: Compute cell offsets relative to locals in compiler. Allows the
interpreter to treats locals and cells a single array, which is slightly
more efficient. Also make the LOAD_CLOSURE opcode an alias for LOAD_FAST.
Preserving LOAD_CLOSURE helps keep bytecode a bit more readable.

- bpo-17792: More accurate error messages for access of unbound locals or
free vars.

- bpo-28146: Fix a confusing error message in :func:`str.format`.

- bpo-11105: When compiling :class:`ast.AST` objects with recursive
references through :func:`compile`, the interpreter doesn't crash anymore
instead it raises a :exc:`RecursionError`.

- bpo-39091: Fix crash when using passing a non-exception to a generator's
``throw()`` method. Patch by Noah Oxer

- bpo-33346: Asynchronous comprehensions are now allowed inside
comprehensions in asynchronous functions. Outer comprehensions implicitly
become asynchronous.

Library
-------

- bpo-45371: Fix clang rpath issue in :mod:`distutils`. The UnixCCompiler
now uses correct clang option to add a runtime library directory (rpath)
to a shared library.

- bpo-45329: Fix freed memory access in :class:`pyexpat.xmlparser` when
building it with an installed expat library <= 2.2.0.

- bpo-41710: On Unix, if the ``sem_clockwait()`` function is available in
the C library (glibc 2.30 and newer), the :meth:`threading.Lock.acquire`
method now uses the monotonic clock (:data:`time.CLOCK_MONOTONIC`) for the
timeout, rather than using the system clock (:data:`time.CLOCK_REALTIME`),
to not be affected by system clock changes. Patch by Victor Stinner.

- bpo-1596321: Fix the :func:`threading._shutdown` function when the
:mod:`threading` module was imported first from a thread different than
the main thread: no longer log an error at Python exit.

- bpo-45274: Fix a race condition in the :meth:`Thread.join()
<threading.Thread.join>` method of the :mod:`threading` module. If the
function is interrupted by a signal and the signal handler raises an
exception, make sure that the thread remains in a consistent state to
prevent a deadlock. Patch by Victor Stinner.

- bpo-21302: In Unix operating systems, :func:`time.sleep` now uses the
``nanosleep()`` function, if ``clock_nanosleep()`` is not available but
``nanosleep()`` is available. ``nanosleep()`` allows to sleep with
nanosecond precision.

- bpo-21302: On Windows, :func:`time.sleep` now uses a waitable timer which
has a resolution of 100 nanoseconds (10\ :sup:`-7` seconds). Previously,
it had a resolution of 1 millisecond (10\ :sup:`-3` seconds). Patch by
Benjamin Szőke and Victor Stinner.

- bpo-45238: Fix :meth:`unittest.IsolatedAsyncioTestCase.debug`: it runs now
asynchronous methods and callbacks.

- bpo-36674: :meth:`unittest.TestCase.debug` raises now a
:class:`unittest.SkipTest` if the class or the test method are decorated
with the skipping decorator.

- bpo-45235: Fix an issue where argparse would not preserve values in a
provided namespace when using a subparser with defaults.

- bpo-45183: Have zipimport.zipimporter.find_spec() not raise an exception
when the underlying zip file has been deleted and the internal cache has
been reset via invalidate_cache().

- bpo-45234: Fixed a regression in :func:`~shutil.copyfile`,
:func:`~shutil.copy`, :func:`~shutil.copy2` raising
:exc:`FileNotFoundError` when source is a directory, which should raise
:exc:`IsADirectoryError`

- bpo-45228: Fix stack buffer overflow in parsing J1939 network address.

- bpo-45225: use map function instead of genexpr in capwords.

- bpo-42135: Fix typo: ``importlib.find_loader`` is really slated for
removal in Python 3.12 not 3.10, like the others in PR 25169.

Patch by Hugo van Kemenade.

- bpo-20524: Improves error messages on ``.format()`` operation for ``str``,
``float``, ``int``, and ``complex``. New format now shows the problematic
pattern and the object type.

- bpo-45168: Change :func:`dis.dis` output to omit op arg values that cannot
be resolved due to ``co_consts``, ``co_names`` etc not being provided.
Previously the oparg itself was repeated in the value field, which is not
useful and can be confusing.

- bpo-21302: In Unix operating systems, :func:`time.sleep` now uses the
``clock_nanosleep()`` function, if available, which allows to sleep for an
interval specified with nanosecond precision.

- bpo-45173: Remove from the :mod:`configparser` module: the
:class:`SafeConfigParser` class, the :attr:`filename` property of the
:class:`ParsingError` class, the :meth:`readfp` method of the
:class:`ConfigParser` class, deprecated since Python 3.2.

Patch by Hugo van Kemenade.

- bpo-44987: Pure ASCII strings are now normalized in constant time by
:func:`unicodedata.normalize`. Patch by Dong-hee Na.

- bpo-35474: Calling :func:`mimetypes.guess_all_extensions` with
``strict=False`` no longer affects the result of the following call with
``strict=True``. Also, mutating the returned list no longer affects the
global state.

- bpo-45166: :func:`typing.get_type_hints` now works with
:data:`~typing.Final` wrapped in :class:`~typing.ForwardRef`.

- bpo-45162: Remove many old deprecated :mod:`unittest` features:

* "``fail*``" and "``assert*``" aliases of :class:`~unittest.TestCase` methods.
* Broken from start :class:`~unittest.TestCase` method ``assertDictContainsSubset()``.
* Ignored :meth:`<unittest.TestLoader.loadTestsFromModule> TestLoader.loadTestsFromModule` parameter *use_load_tests*.
* Old alias ``_TextTestResult`` of :class:`~unittest.TextTestResult`.

- bpo-38371: Remove the deprecated ``split()`` method of
:class:`_tkinter.TkappType`. Patch by Erlend E. Aasland.

- bpo-20499: Improve the speed and accuracy of statistics.pvariance().

- bpo-45132: Remove :meth:`__getitem__` methods of
:class:`xml.dom.pulldom.DOMEventStream`, :class:`wsgiref.util.FileWrapper`
and :class:`fileinput.FileInput`, deprecated since Python 3.9.

Patch by Hugo van Kemenade.

- bpo-45129: Due to significant security concerns, the *reuse_address*
parameter of :meth:`asyncio.loop.create_datagram_endpoint`, disabled in
Python 3.9, is now entirely removed. This is because of the behavior of
the socket option ``SO_REUSEADDR`` in UDP.

Patch by Hugo van Kemenade.

- bpo-45124: The ``bdist_msi`` command, deprecated in Python 3.9, is now
removed.

Use ``bdist_wheel`` (wheel packages) instead.

Patch by Hugo van Kemenade.

- bpo-30856: :class:`unittest.TestResult` methods
:meth:`~unittest.TestResult.addFailure`,
:meth:`~unittest.TestResult.addError`,
:meth:`~unittest.TestResult.addSkip` and
:meth:`~unittest.TestResult.addSubTest` are now called immediately after
raising an exception in test or finishing a subtest. Previously they were
called only after finishing the test clean up.

- bpo-45034: Changes how error is formatted for ``struct.pack`` with ``'H'``
and ``'h'`` modes and too large / small numbers. Now it shows the actual
numeric limits, while previously it was showing arithmetic expressions.

- bpo-25894: :mod:`unittest` now always reports skipped and failed subtests
separately: separate characters in default mode and separate lines in
verbose mode. Also the test description is now output for errors in test
method, class and module cleanups.

- bpo-45081: Fix issue when dataclasses that inherit from
``typing.Protocol`` subclasses have wrong ``__init__``. Patch provided by
Yurii Karabas.

- bpo-45085: The ``binhex`` module, deprecated in Python 3.9, is now
removed. The following :mod:`binascii` functions, deprecated in Python
3.9, are now also removed:

* ``a2b_hqx()``, ``b2a_hqx()``;
* ``rlecode_hqx()``, ``rledecode_hqx()``.

The :func:`binascii.crc_hqx` function remains available.

Patch by Victor Stinner.

- bpo-40360: The :mod:`lib2to3` package is now deprecated and may not be
able to parse Python 3.10 or newer. See the :pep:`617` (New PEG parser for
CPython). Patch by Victor Stinner.

- bpo-45075: Rename :meth:`traceback.StackSummary.format_frame` to
:meth:`traceback.StackSummary.format_frame_summary`. This method was added
for 3.11 so it was not released yet.

Updated code and docs to better distinguish frame and FrameSummary.

- bpo-31299: Add option to completely drop frames from a traceback by
returning ``None`` from a :meth:`~traceback.StackSummary.format_frame`
override.

- bpo-41620: :meth:`~unittest.TestCase.run` now always return a
:class:`~unittest.TestResult` instance. Previously it returned ``None`` if
the test class or method was decorated with a skipping decorator.

- bpo-45021: Fix a potential deadlock at shutdown of forked children when
using :mod:`concurrent.futures` module

- bpo-43913: Fix bugs in cleaning up classes and modules in :mod:`unittest`:

* Functions registered with :func:`~unittest.addModuleCleanup` were not called unless the user defines ``tearDownModule()`` in their test module.
* Functions registered with :meth:`~unittest.TestCase.addClassCleanup` were not called if ``tearDownClass`` is set to ``None``.
* Buffering in :class:`~unittest.TestResult` did not work with functions registered with ``addClassCleanup()`` and ``addModuleCleanup()``.
* Errors in functions registered with ``addClassCleanup()`` and ``addModuleCleanup()`` were not handled correctly in buffered and debug modes.
* Errors in ``setUpModule()`` and functions registered with ``addModuleCleanup()`` were reported in wrong order.
* And several lesser bugs.

- bpo-45030: Fix integer overflow in pickling and copying the range
iterator.

- bpo-45001: Made email date parsing more robust against malformed input,
namely a whitespace-only ``Date:`` header. Patch by Wouter Bolsterlee.

- bpo-45010: Remove support of special method ``__div__`` in
:mod:`unittest.mock`. It is not used in Python 3.

- bpo-39218: Improve accuracy of variance calculations by using ``x*x``
instead of ``x**2``.

- bpo-43613: Improve the speed of :func:`gzip.compress` and
:func:`gzip.decompress` by compressing and decompressing at once in memory
instead of in a streamed fashion.

- bpo-37596: Ensure that :class:`set` and :class:`frozenset` objects are
always :mod:`marshalled <marshal>` reproducibly.

- bpo-44019: A new function ``operator.call`` has been added, such that
``operator.call(obj, *args, **kwargs) == obj(*args, **kwargs)``.

- bpo-42255: :class:`webbrowser.MacOSX` is deprecated and will be removed in
Python 3.13. It is untested and undocumented and also not used by
webbrowser itself. Patch by Dong-hee Na.

- bpo-44955: Method :meth:`~unittest.TestResult.stopTestRun` is now always
called in pair with method :meth:`~unittest.TestResult.startTestRun` for
:class:`~unittest.TestResult` objects implicitly created in
:meth:`~unittest.TestCase.run`. Previously it was not called for test
methods and classes decorated with a skipping decorator.

- bpo-39039: tarfile.open raises :exc:`~tarfile.ReadError` when a zlib error
occurs during file extraction.

- bpo-44935: :mod:`subprocess` on Solaris now also uses
:func:`os.posix_spawn()` for better performance.

- bpo-44911: :class:`~unittest.IsolatedAsyncioTestCase` will no longer throw
an exception while cancelling leaked tasks. Patch by Bar Harel.

- bpo-41322: Added ``DeprecationWarning`` for tests and async tests that
return a value!=None (as this may indicate an improperly written test, for
example a test written as a generator function).

- bpo-44524: Make exception message more useful when subclass from typing
special form alias. Patch provided by Yurii Karabas.

- bpo-38956: :class:`argparse.BooleanOptionalAction`'s default value is no
longer printed twice when used with
:class:`argparse.ArgumentDefaultsHelpFormatter`.

- bpo-44860: Fix the ``posix_user`` scheme in :mod:`sysconfig` to not depend
on :data:`sys.platlibdir`.

- bpo-44859: Improve error handling in :mod:`sqlite3` and raise more
accurate exceptions.

* :exc:`MemoryError` is now raised instead of :exc:`sqlite3.Warning` when memory is not enough for encoding a statement to UTF-8 in ``Connection.__call__()`` and ``Cursor.execute()``.
* :exc:`UnicodEncodeError` is now raised instead of :exc:`sqlite3.Warning` when the statement contains surrogate characters in ``Connection.__call__()`` and ``Cursor.execute()``.
* :exc:`TypeError` is now raised instead of :exc:`ValueError` for non-string script argument in ``Cursor.executescript()``.
* :exc:`ValueError` is now raised for script containing the null character instead of truncating it in ``Cursor.executescript()``.
* Correctly handle exceptions raised when getting boolean value of the result of the progress handler.
* Add many tests covering different corner cases.

- bpo-44581: Upgrade bundled pip to 21.2.3 and setuptools to 57.4.0

- bpo-44849: Fix the :func:`os.set_inheritable` function on FreeBSD 14 for
file descriptor opened with the :data:`~os.O_PATH` flag: ignore the
:data:`~errno.EBADF` error on ``ioctl()``, fallback on the ``fcntl()``
implementation. Patch by Victor Stinner.

- bpo-44605: The @functools.total_ordering() decorator now works with
metaclasses.

- bpo-44524: Fixed an issue wherein the ``__name__`` and ``__qualname__``
attributes of subscribed specialforms could be ``None``.

- bpo-44839: :class:`MemoryError` raised in user-defined functions will now
produce a ``MemoryError`` in :mod:`sqlite3`. :class:`OverflowError` will
now be converted to :class:`~sqlite3.DataError`. Previously
:class:`~sqlite3.OperationalError` was produced in these cases.

- bpo-44822: :mod:`sqlite3` user-defined functions and aggregators returning
:class:`strings <str>` with embedded NUL characters are no longer
truncated. Patch by Erlend E. Aasland.

- bpo-44801: Ensure that the :class:`~typing.ParamSpec` variable in Callable
can only be substituted with a parameters expression (a list of types, an
ellipsis, ParamSpec or Concatenate).

- bpo-44806: Non-protocol subclasses of :class:`typing.Protocol` ignore now
the ``__init__`` method inherited from protocol base classes.

- bpo-27275: :meth:`collections.OrderedDict.popitem` and
:meth:`collections.OrderedDict.pop` no longer call ``__getitem__`` and
``__delitem__`` methods of the OrderedDict subclasses.

- bpo-44793: Fix checking the number of arguments when subscribe a generic
type with ``ParamSpec`` parameter.

- bpo-44784: In importlib.metadata tests, override warnings behavior under
expected DeprecationWarnings (importlib_metadata 4.6.3).

- bpo-44667: The :func:`tokenize.tokenize` doesn't incorrectly generate a
``NEWLINE`` token if the source doesn't end with a new line character but
the last line is a comment, as the function is already generating a ``NL``
token. Patch by Pablo Galindo

- bpo-44771: Added ``importlib.simple`` module implementing adapters from a
low-level resources reader interface to a ``TraversableResources``
interface. Legacy API (``path``, ``contents``, ...) is now supported
entirely by the ``.files()`` API with a compatibility shim supplied for
resource loaders without that functionality. Feature parity with
``importlib_resources`` 5.2.

- bpo-44752: :mod:`rcompleter` does not call :func:`getattr` on
:class:`property` objects to avoid the side-effect of evaluating the
corresponding method.

- bpo-44747: Refactor usage of ``sys._getframe`` in ``typing`` module. Patch
provided by Yurii Karabas.

- bpo-42378: Fixes the issue with log file being overwritten when
:class:`logging.FileHandler` is used in :mod:`atexit` with *filemode* set
to ``'w'``. Note this will cause the message in *atexit* not being logged
if the log stream is already closed due to shutdown of logging.

- bpo-44720: ``weakref.proxy`` objects referencing non-iterators now raise
``TypeError`` rather than dereferencing the null ``tp_iternext`` slot and
crashing.

- bpo-44704: The implementation of ``collections.abc.Set._hash()`` now
matches that of ``frozenset.__hash__()``.

- bpo-44666: Fixed issue in :func:`compileall.compile_file` when
``sys.stdout`` is redirected. Patch by Stefan Hölzl.

- bpo-44688: :meth:`sqlite3.Connection.create_collation` now accepts
non-ASCII collation names. Patch by Erlend E. Aasland.

- bpo-44690: Adopt *binacii.a2b_base64*'s strict mode in *base64.b64decode*.

- bpo-42854: Fixed a bug in the :mod:`_ssl` module that was throwing
:exc:`OverflowError` when using :meth:`_ssl._SSLSocket.write` and
:meth:`_ssl._SSLSocket.read` for a big value of the ``len`` parameter.
Patch by Pablo Galindo

- bpo-44686: Replace ``unittest.mock._importer`` with
``pkgutil.resolve_name``.

- bpo-44353: Make ``NewType.__call__`` faster by implementing it in C. Patch
provided by Yurii Karabas.

- bpo-44682: Change the :mod:`pdb` *commands* directive to disallow setting
commands for an invalid breakpoint and to display an appropriate error.

- bpo-44353: Refactor ``typing.NewType`` from function into callable class.
Patch provided by Yurii Karabas.

- bpo-44678: Added a separate error message for discontinuous padding in
*binascii.a2b_base64* strict mode.

- bpo-44524: Add missing ``__name__`` and ``__qualname__`` attributes to
``typing`` module classes. Patch provided by Yurii Karabas.

- bpo-40897: Give priority to using the current class constructor in
:func:`inspect.signature`. Patch by Weipeng Hong.

- bpo-44638: Add a reference to the zipp project and hint as to how to use
it.

- bpo-44648: Fixed wrong error being thrown by :func:`inspect.getsource`
when examining a class in the interactive session. Instead of
:exc:`TypeError`, it should be :exc:`OSError` with appropriate error
message.

- bpo-44608: Fix memory leak in :func:`_tkinter._flatten` if it is called
with a sequence or set, but not list or tuple.

- bpo-44594: Fix an edge case of :class:`ExitStack` and
:class:`AsyncExitStack` exception chaining. They will now match ``with``
block behavior when ``__context__`` is explicitly set to ``None`` when the
exception is in flight.

- bpo-42799: In :mod:`fnmatch`, the cache size for compiled regex patterns
(:func:`functools.lru_cache`) was bumped up from 256 to 32768, affecting
functions: :func:`fnmatch.fnmatch`, :func:`fnmatch.fnmatchcase`,
:func:`fnmatch.filter`.

- bpo-41928: Update :func:`shutil.copyfile` to raise
:exc:`FileNotFoundError` instead of confusing :exc:`IsADirectoryError`
when a path ending with a :const:`os.path.sep` does not exist;
:func:`shutil.copy` and :func:`shutil.copy2` are also affected.

- bpo-44569: Added the :func:`StackSummary.format_frame` function in
:mod:`traceback`. This allows users to customize the way individual lines
are formatted in tracebacks without re-implementing logic to handle
recursive tracebacks.

- bpo-44566: handle StopIteration subclass raised from
@contextlib.contextmanager generator

- bpo-44558: Make the implementation consistency of
:func:`~operator.indexOf` between C and Python versions. Patch by Dong-hee
Na.

- bpo-41249: Fixes ``TypedDict`` to work with ``typing.get_type_hints()``
and postponed evaluation of annotations across modules.

- bpo-44554: Refactor argument processing in :func:`pdb.main` to simplify
detection of errors in input loading and clarify behavior around module or
script invocation.

- bpo-34798: Break up paragraph about :class:`pprint.PrettyPrinter`
construction parameters to make it easier to read.

- bpo-44539: Added support for recognizing JPEG files without JFIF or Exif
markers.

- bpo-44461: Fix bug with :mod:`pdb`'s handling of import error due to a
package which does not have a ``__main__`` module

- bpo-43625: Fix a bug in the detection of CSV file headers by
:meth:`csv.Sniffer.has_header` and improve documentation of same.

- bpo-44516: Update vendored pip to 21.1.3

- bpo-42892: Fixed an exception thrown while parsing a malformed multipart
email by :class:`email.message.EmailMessage`.

- bpo-44468: :func:`typing.get_type_hints` now finds annotations in classes
and base classes with unexpected ``__module__``. Previously, it skipped
those MRO elements.

- bpo-44491: Allow clearing the :mod:`sqlite3` authorizer callback by
passing :const:`None` to :meth:`~sqlite3.Connection.set_authorizer`. Patch
by Erlend E. Aasland.

- bpo-43977: Set the proper :const:`Py_TPFLAGS_MAPPING` and
:const:`Py_TPFLAGS_SEQUENCE` flags for subclasses created before a parent
has been registered as a :class:`collections.abc.Mapping` or
:class:`collections.abc.Sequence`.

- bpo-44482: Fix very unlikely resource leak in :mod:`glob` in alternate
Python implementations.

- bpo-44466: The :mod:`faulthandler` module now detects if a fatal error
occurs during a garbage collector collection. Patch by Victor Stinner.

- bpo-44471: A :exc:`TypeError` is now raised instead of an
:exc:`AttributeError` in :meth:`contextlib.ExitStack.enter_context` and
:meth:`contextlib.AsyncExitStack.enter_async_context` for objects which do
not support the :term:`context manager` or :term:`asynchronous context
manager` protocols correspondingly.

- bpo-44404: :mod:`tkinter`'s ``after()`` method now supports callables
without the ``__name__`` attribute.

- bpo-41546: Make :mod:`pprint` (like the builtin ``print``) not attempt to
write to ``stdout`` when it is ``None``.

- bpo-44458: ``BUFFER_BLOCK_SIZE`` is now declared static, to avoid linking
collisions when bz2, lmza or zlib are statically linked.

- bpo-44464: Remove exception for flake8 in deprecated importlib.metadata
interfaces. Sync with importlib_metadata 4.6.

- bpo-44446: Take into account that ``lineno`` might be ``None`` in
:class:`traceback.FrameSummary`.

- bpo-44439: Fix in :meth:`bz2.BZ2File.write` / :meth:`lzma.LZMAFile.write`
methods, when the input data is an object that supports the buffer
protocol, the file length may be wrong.

- bpo-44434: _thread.start_new_thread() no longer calls
PyThread_exit_thread() explicitly at the thread exit, the call was
redundant. On Linux with the glibc, pthread_exit() aborts the whole
process if dlopen() fails to open libgcc_s.so file (ex: EMFILE error).
Patch by Victor Stinner.

- bpo-42972: The _thread.RLock type now fully implement the GC protocol: add
a traverse function and the :const:`Py_TPFLAGS_HAVE_GC` flag. Patch by
Victor Stinner.

- bpo-44422: The :func:`threading.enumerate` function now uses a reentrant
lock to prevent a hang on reentrant call. Patch by Victor Stinner.

- bpo-38291: Importing typing.io or typing.re now prints a
``DeprecationWarning``.

- bpo-37880: argparse actions store_const and append_const each receive a
default value of None when the ``const`` kwarg is not provided.
Previously, this raised a :exc:`TypeError`.

- bpo-44389: Fix deprecation of :data:`ssl.OP_NO_TLSv1_3`

- bpo-27827: :meth:`pathlib.PureWindowsPath.is_reserved` now identifies a
greater range of reserved filenames, including those with trailing spaces
or colons.

- bpo-44395: Fix :meth:`~email.message.MIMEPart.as_string` to pass unixfrom
properly. Patch by Dong-hee Na.

- bpo-34266: Handle exceptions from parsing the arg of :mod:`pdb`'s
run/restart command.

- bpo-44362: Improve :mod:`ssl` module's deprecation messages, error
reporting, and documentation for deprecations.

- bpo-44342: [Enum] Change pickling from by-value to by-name.

- bpo-44356: [Enum] Allow multiple data-type mixins if they are all the
same.

- bpo-44351: Restore back :func:`parse_makefile` in
:mod:`distutils.sysconfig` because it behaves differently than the similar
implementation in :mod:`sysconfig`.

- bpo-35800: :class:`smtpd.MailmanProxy` is now removed as it is unusable
without an external module, ``mailman``. Patch by Dong-hee Na.

- bpo-44357: Added a function that returns cube root of the given number
:func:`math.cbrt`

- bpo-44339: Change ``math.pow(±0.0, -math.inf)`` to return ``inf`` instead
of raising ``ValueError``. This brings the special-case handling of
``math.pow`` into compliance with the IEEE 754 standard.

- bpo-44242: Remove missing flag check from Enum creation and move into a
``verify`` decorator.

- bpo-44246: In ``importlib.metadata``, restore compatibility in the result
from ``Distribution.entry_points`` (``EntryPoints``) to honor expectations
in older implementations and issuing deprecation warnings for these cases:
A. ``EntryPoints`` objects are once again mutable, allowing for
``sort()`` and other list-based mutation operations. Avoid deprecation
warnings by casting to a mutable sequence (e.g.
``list(dist.entry_points).sort()``). B. ``EntryPoints`` results once again
allow for access by index. To avoid deprecation warnings, cast the
result to a Sequence first (e.g. ``tuple(dist.entry_points)[0]``).

- bpo-44246: In importlib.metadata.entry_points, de-duplication of
distributions no longer requires loading the full metadata for
PathDistribution objects, improving entry point loading performance by
~10x.

- bpo-43858: Added a function that returns a copy of a dict of logging
levels: :func:`logging.getLevelNamesMapping`

- bpo-44260: The :class:`random.Random` constructor no longer reads system
entropy without need.

- bpo-44254: On Mac, give turtledemo button text a color that works on both
light or dark background. Programmers cannot control the latter.

- bpo-44258: Support PEP 515 for Fraction's initialization from string.

- bpo-44235: Remove deprecated functions in the :mod:`gettext`. Patch by
Dong-hee Na.

- bpo-38693: Prefer f-strings to ``.format`` in importlib.resources.

- bpo-33693: Importlib.metadata now prefers f-strings to .format.

- bpo-44241: Incorporate minor tweaks from importlib_metadata 4.1:
SimplePath protocol, support for Metadata 2.2.

- bpo-43216: Remove the :func:`@asyncio.coroutine <asyncio.coroutine>`
:term:`decorator` enabling legacy generator-based coroutines to be
compatible with async/await code; remove
:class:`asyncio.coroutines.CoroWrapper` used for wrapping legacy coroutine
objects in the debug mode. The decorator has been deprecated since Python
3.8 and the removal was initially scheduled for Python 3.10. Patch by
Illia Volochii.

- bpo-44210: Make importlib.metadata._meta.PackageMetadata public.

- bpo-43643: Declare readers.MultiplexedPath.name as a property per the
spec.

- bpo-27334: The :mod:`sqlite3` context manager now performs a rollback
(thus releasing the database lock) if commit failed. Patch by Luca Citi
and Erlend E. Aasland.

- bpo-4928: Documented existing behavior on POSIX: NamedTemporaryFiles are
not deleted when creating process is killed with SIGKILL

- bpo-44154: Optimize :class:`fractions.Fraction` pickling for large
components.

- bpo-33433: For IPv4 mapped IPv6 addresses (:rfc:`4291` Section 2.5.5.2),
the :mod:`ipaddress.IPv6Address.is_private` check is deferred to the
mapped IPv4 address. This solves a bug where public mapped IPv4 addresses
were considered private by the IPv6 check.

- bpo-44150: Add optional *weights* argument to statistics.fmean().

- bpo-44142: :func:`ast.unparse` will now drop the redundant parentheses
when tuples used as assignment targets (e.g in for loops).

- bpo-44145: :mod:`hmac` computations were not releasing the GIL while
calling the OpenSSL ``HMAC_Update`` C API (a new feature in 3.9). This
unintentionally prevented parallel computation as other :mod:`hashlib`
algorithms support.

- bpo-44095: :class:`zipfile.Path` now supports :attr:`zipfile.Path.stem`,
:attr:`zipfile.Path.suffixes`, and :attr:`zipfile.Path.suffix` attributes.

- bpo-44077: It's now possible to receive the type of service (ToS), a.k.a.
differentiated services (DS), a.k.a. differentiated services code point
(DSCP) and explicit congestion notification (ECN) IP header fields with
``socket.IP_RECVTOS``.

- bpo-37788: Fix a reference leak when a Thread object is never joined.

- bpo-38908: Subclasses of ``typing.Protocol`` which only have data
variables declared will now raise a ``TypeError`` when checked with
``isinstance`` unless they are decorated with :func:`runtime_checkable`.
Previously, these checks passed silently. Patch provided by Yurii Karabas.

- bpo-44098: ``typing.ParamSpec`` will no longer be found in the
``__parameters__`` of most :mod:`typing` generics except in valid use
locations specified by :pep:`612`. This prevents incorrect usage like
``typing.List[P][int]``. This change means incorrect usage which may have
passed silently in 3.10 beta 1 and earlier will now error.

- bpo-44089: Allow subclassing ``csv.Error`` in 3.10 (it was allowed in 3.9
and earlier but was disallowed in early versions of 3.10).

- bpo-44081: :func:`ast.unparse` now doesn't use redundant spaces to
separate ``lambda`` and the ``:`` if there are no parameters.

- bpo-44061: Fix regression in previous release when calling
:func:`pkgutil.iter_modules` with a list of :class:`pathlib.Path` objects

- bpo-44059: Register the SerenityOS Browser in the :mod:`webbrowser`
module.

- bpo-36515: The :mod:`hashlib` module no longer does unaligned memory
accesses when compiled for ARM platforms.

- bpo-40465: Remove random module features deprecated in Python 3.9.

- bpo-44018: random.seed() no longer mutates bytearray inputs.

- bpo-38352: Add ``IO``, ``BinaryIO``, ``TextIO``, ``Match``, and
``Pattern`` to ``typing.__all__``. Patch by Jelle Zijlstra.

- bpo-44002: :mod:`urllib.parse` now uses :func:`functool.lru_cache` for its
internal URL splitting and quoting caches instead of rolling its own like
its the '90s.

The undocumented internal :mod:`urllib.parse` ``Quoted`` class API is now
deprecated, for removal in 3.14.

- bpo-43972: When :class:`http.server.SimpleHTTPRequestHandler` sends a
``301 (Moved Permanently)`` for a directory path not ending with `/`, add
a ``Content-Length: 0`` header. This improves the behavior for certain
clients.

- bpo-28528: Fix a bug in :mod:`pdb` where :meth:`~pdb.Pdb.checkline` raises
:exc:`AttributeError` if it is called after :meth:`~pdb.Pdb.reset`.

- bpo-43853: Improved string handling for :mod:`sqlite3` user-defined
functions and aggregates:

* It is now possible to pass strings with embedded null characters to UDFs
* Conversion failures now correctly raise :exc:`MemoryError`

Patch by Erlend E. Aasland.

- bpo-43666: AIX: `Lib/_aix_support.get_platform()` may fail in an AIX WPAR.
The fileset bos.rte appears to have a builddate in both LPAR and WPAR so
this fileset is queried rather than bos.mp64. To prevent a similar
situation (no builddate in ODM) a value (9988) sufficient for completing a
build is provided. Patch by M Felt.

- bpo-43650: Fix :exc:`MemoryError` in :func:`shutil.unpack_archive` which
fails inside :func:`shutil._unpack_zipfile` on large files. Patch by Igor
Bolshakov.

- bpo-43612: :func:`zlib.compress` now accepts a wbits parameter which
allows users to compress data as a raw deflate block without zlib headers
and trailers in one go. Previously this required instantiating a
``zlib.compressobj``. It also provides a faster alternative to
``gzip.compress`` when wbits=31 is used.

- bpo-43392: :func:`importlib._bootstrap._find_and_load` now implements a
two-step check to avoid locking when modules have been already imported
and are ready. This improves performance of repeated calls to
:func:`importlib.import_module` and :func:`importlib.__import__`.

- bpo-43318: Fix a bug where :mod:`pdb` does not always echo cleared
breakpoints.

- bpo-43234: Prohibit passing
non-:class:`concurrent.futures.ThreadPoolExecutor` executors to
:meth:`loop.set_default_executor` following a deprecation in Python 3.8.
Patch by Illia Volochii.

- bpo-43232: Prohibit previously deprecated potentially disruptive
operations on :class:`asyncio.trsock.TransportSocket`. Patch by Illia
Volochii.

- bpo-30077: Added support for Apple's aifc/sowt pseudo-compression

- bpo-42971: Add definition of ``errno.EQFULL`` for platforms that define
this constant (such as macOS).

- bpo-43086: Added a new optional :code:`strict_mode` parameter to
*binascii.a2b_base64*. When :code:`scrict_mode` is set to :code:`True`,
the *a2b_base64* function will accept only valid base64 content. More
details about what "valid base64 content" is, can be found in the
function's documentation.

- bpo-43024: Improve the help signature of
:func:`traceback.print_exception`, :func:`traceback.format_exception` and
:func:`traceback.format_exception_only`.

- bpo-33809: Add the :meth:`traceback.TracebackException.print` method which
prints the formatted exception information.

- bpo-42862: :mod:`sqlite3` now utilizes :meth:`functools.lru_cache` to
implement the connection statement cache. As a small optimisation, the
default statement cache size has been increased from 100 to 128. Patch by
Erlend E. Aasland.

- bpo-41818: Soumendra Ganguly: add termios.tcgetwinsize(),
termios.tcsetwinsize().

- bpo-40497: :meth:`subprocess.check_output` now raises :exc:`ValueError`
when the invalid keyword argument *check* is passed by user code.
Previously such use would fail later with a :exc:`TypeError`. Patch by
Rémi Lapeyre.

- bpo-37449: ``ensurepip`` now uses ``importlib.resources.files()``
traversable APIs

- bpo-40956: Use Argument Clinic in :mod:`sqlite3`. Patches by Erlend E.
Aasland.

- bpo-41730: ``DeprecationWarning`` is now raised when importing
:mod:`tkinter.tix`, which has been deprecated in documentation since
Python 3.6.

- bpo-20684: Remove unused ``_signature_get_bound_param`` function from
:mod:`inspect` - by Anthony Sottile.

- bpo-41402: Fix :meth:`email.message.EmailMessage.set_content` when called
with binary data and ``7bit`` content transfer encoding.

- bpo-32695: The *compresslevel* and *preset* keyword arguments of
:func:`tarfile.open` are now both documented and tested.

- bpo-41137: Use utf-8 encoding while reading .pdbrc files. Patch by
Srinivas Reddy Thatiparthy

- bpo-24391: Improved reprs of :mod:`threading` synchronization objects:
:class:`~threading.Semaphore`, :class:`~threading.BoundedSemaphore`,
:class:`~threading.Event` and :class:`~threading.Barrier`.

- bpo-5846: Deprecated the following :mod:`unittest` functions, scheduled
for removal in Python 3.13:

* :func:`~unittest.findTestCases`
* :func:`~unittest.makeSuite`
* :func:`~unittest.getTestCaseNames`

Use :class:`~unittest.TestLoader` methods instead:

* :meth:`unittest.TestLoader.loadTestsFromModule`
* :meth:`unittest.TestLoader.loadTestsFromTestCase`
* :meth:`unittest.TestLoader.getTestCaseNames`

Patch by Erlend E. Aasland.

- bpo-40563: Support pathlike objects on dbm/shelve. Patch by Hakan Çelik
and Henry-Joseph Audéoud.

- bpo-34990: Fixed a Y2k38 bug in the compileall module where it would fail
to compile files with a modification time after the year 2038.

- bpo-39549: Whereas the code for reprlib.Repr had previously used a
hardcoded string value of '...', this PR updates it to use of a
“fillvalue” attribute, whose value defaults to '...' and can be reset in
either individual reprlib.Repr instances or in subclasses thereof.

- bpo-37022: :mod:`pdb` now displays exceptions from ``repr()`` with its
``p`` and ``pp`` commands.

- bpo-38840: Fix ``test___all__`` on platforms lacking a shared memory
implementation.

- bpo-39359: Add one missing check that the password is a bytes object for
an encrypted zipfile.

- bpo-38741: :mod:`configparser`: using ']' inside a section header will no
longer cut the section name short at the ']'

- bpo-38415: Added missing behavior to
:func:`contextlib.asynccontextmanager` to match
:func:`contextlib.contextmanager` so decorated functions can themselves be
decorators.

- bpo-30256: Pass multiprocessing BaseProxy argument ``manager_owned``
through AutoProxy.

- bpo-27513: :func:`email.utils.getaddresses` now accepts
:class:`email.header.Header` objects along with string values. Patch by
Zackery Spytz.

- bpo-16379: Add SQLite error code and name to :mod:`sqlite3` exceptions.
Patch by Aviv Palivoda, Daniel Shahaf, and Erlend E. Aasland.

- bpo-26228: pty.spawn no longer hangs on FreeBSD, macOS, and Solaris.

- bpo-33349: lib2to3 now recognizes async generators everywhere.

- bpo-29298: Fix ``TypeError`` when required subparsers without ``dest`` do
not receive arguments. Patch by Anthony Sottile.

Documentation
-------------

- bpo-45216: Remove extra documentation listing methods in ``difflib``. It
was rendering twice in pydoc and was outdated in some places.

- bpo-45024: :mod:`collections.abc` documentation has been expanded to
explicitly cover how instance and subclass checks work, with additional
doctest examples and an exhaustive list of ABCs which test membership
purely by presence of the right :term:`special method`\s. Patch by Raymond
Hettinger.

- bpo-44957: Promote PEP 604 union syntax by using it where possible. Also,
mention ``X | Y`` more prominently in section about ``Union`` and mention
``X | None`` at all in section about ``Optional``.

- bpo-16580: Added code equivalents for the :meth:`int.to_bytes` and
:meth:`int.from_bytes` methods, as well as tests ensuring that these code
equivalents are valid.

- bpo-44903: Removed the othergui.rst file, any references to it, and the
list of GUI frameworks in the FAQ. In their place I've added links to the
Python Wiki `page on GUI frameworks
<https://wiki.python.org/moin/GuiProgramming>`.

- bpo-33479: Tkinter documentation has been greatly expanded with new
"Architecture" and "Threading model" sections.

- bpo-36700: :mod:`base64` RFC references were updated to point to
:rfc:`4648`; a section was added to point users to the new "security
considerations" section of the RFC.

- bpo-44740: Replaced occurrences of uppercase "Web" and "Internet" with
lowercase versions per the 2016 revised Associated Press Style Book.

- bpo-44693: Update the definition of __future__ in the glossary by
replacing the confusing word "pseudo-module" with a more accurate
description.

- bpo-35183: Add typical examples to os.path.splitext docs

- bpo-30511: Clarify that :func:`shutil.make_archive` is not thread-safe due
to reliance on changing the current working directory.

- bpo-44561: Update of three expired hyperlinks in
Doc/distributing/index.rst: "Project structure", "Building and packaging
the project", and "Uploading the project to the Python Packaging Index".

- bpo-44651: Delete entry "coercion" in Doc/glossary.rst for its outdated
definition.

- bpo-42958: Updated the docstring and docs of :func:`filecmp.cmp` to be
more accurate and less confusing especially in respect to *shallow* arg.

- bpo-44631: Refactored the ``repr()`` code of the ``_Environ`` (os module).

- bpo-44613: importlib.metadata is no longer provisional.

- bpo-44558: Match the docstring and python implementation of
:func:`~operator.countOf` to the behavior of its c implementation.

- bpo-44544: List all kwargs for :func:`textwrap.wrap`,
:func:`textwrap.fill`, and :func:`textwrap.shorten`. Now, there are nav
links to attributes of :class:`TextWrap`, which makes navigation much
easier while minimizing duplication in the documentation.

- bpo-38062: Clarify that atexit uses equality comparisons internally.

- bpo-40620: Convert examples in tutorial controlflow.rst section 4.3 to be
interpreter-demo style.

- bpo-43066: Added a warning to :mod:`zipfile` docs: filename arg with a
leading slash may cause archive to be un-openable on Windows systems.

- bpo-39452: Rewrote ``Doc/library/__main__.rst``. Broadened scope of the
document to explicitly discuss and differentiate between ``__main__.py``
in packages versus the ``__name__ == '__main__'`` expression (and the
idioms that surround it).

- bpo-13814: In the Design FAQ, answer "Why don't generators support the
with statement?"

- bpo-27752: Documentation of csv.Dialect is more descriptive.

- bpo-44453: Fix documentation for the return type of
:func:`sysconfig.get_path`.

- bpo-44392: Added a new section in the C API documentation for types used
in type hinting. Documented ``Py_GenericAlias`` and
``Py_GenericAliasType``.

- bpo-38291: Mark ``typing.io`` and ``typing.re`` as deprecated since Python
3.8 in the documentation. They were never properly supported by type
checkers.

- bpo-44322: Document that SyntaxError args have a details tuple and that
details are adjusted for errors in f-string field replacement expressions.

- bpo-42392: Document the deprecation and removal of the ``loop`` parameter
for many functions and classes in :mod:`asyncio`.

- bpo-44195: Corrected references to ``TraversableResources`` in docs. There
is no ``TraversableReader``.

- bpo-41963: Document that ``ConfigParser`` strips off comments when reading
configuration files.

- bpo-44072: Correct where in the numeric ABC hierarchy ``**`` support is
added, i.e., in numbers.Complex, not numbers.Integral.

- bpo-43558: Add the remark to :mod:`dataclasses` documentation that the
:meth:`__init__` of any base class has to be called in
:meth:`__post_init__`, along with a code example.

- bpo-44025: Clarify when '_' in match statements is a keyword, and when
not.

- bpo-41706: Fix docs about how methods like ``__add__`` are invoked when
evaluating operator expressions.

- bpo-41621: Document that :class:`collections.defaultdict` parameter
``default_factory`` defaults to None and is positional-only.

- bpo-41576: document BaseException in favor of bare except

- bpo-21760: The description for __file__ fixed. Patch by Furkan Onder

- bpo-39498: Add a "Security Considerations" index which links to standard
library modules that have explicitly documented security considerations.

- bpo-33479: Remove the unqualified claim that tkinter is threadsafe. It has
not been true for several years and likely never was. An explanation of
what is true may be added later, after more discussion, and possibly after
patching _tkinter.c,

Tests
-----

- bpo-40173: Fix :func:`test.support.import_helper.import_fresh_module`.

- bpo-45280: Add a test case for empty :class:`typing.NamedTuple`.

- bpo-45269: Cover case when invalid ``markers`` type is supplied to
``c_make_encoder``.

- bpo-45128: Fix ``test_multiprocessing_fork`` failure due to
``test_logging`` and ``sys.modules`` manipulation.

- bpo-45209: Fix ``UserWarning: resource_tracker`` warning in
``_test_multiprocessing._TestSharedMemory.test_shared_memory_cleaned_after_process_termination``

- bpo-45185: Enables ``TestEnumerations`` test cases in ``test_ssl`` suite.

- bpo-45195: Fix test_readline.test_nonascii(): sometimes, the newline
character is not written at the end, so don't expect it in the output.
Patch by Victor Stinner.

- bpo-45156: Fixes infinite loop on :func:`unittest.mock.seal` of mocks
created by :func:`~unittest.create_autospec`.

- bpo-45125: Improves pickling tests and docs of ``SharedMemory`` and
``SharableList`` objects.

- bpo-44860: Update ``test_sysconfig.test_user_similar()`` for the
posix_user scheme: ``platlib`` doesn't use :data:`sys.platlibdir`. Patch
by Victor Stinner.

- bpo-45052: ``WithProcessesTestSharedMemory.test_shared_memory_basics``
test was ignored, because ``self.assertEqual(sms.size, sms2.size)`` line
was failing. It is now removed and test is unskipped.

The main motivation for this line to be removed from the test is that the
``size`` of ``SharedMemory`` is not ever guaranteed to be the same. It is
decided by the platform.

- bpo-44895: libregrtest now clears the type cache later to reduce the risk
of false alarm when checking for reference leaks. Previously, the type
cache was cleared too early and libregrtest raised a false alarm about
reference leaks under very specific conditions. Patch by Irit Katriel and
Victor Stinner.

- bpo-45042: Fixes that test classes decorated with
``@hashlib_helper.requires_hashdigest`` were skipped all the time.

- bpo-25130: Add calls of :func:`gc.collect` in tests to support PyPy.

- bpo-45011: Made tests relying on the :mod:`_asyncio` C extension module
optional to allow running on alternative Python implementations. Patch by
Serhiy Storchaka.

- bpo-44949: Fix auto history tests of test_readline: sometimes, the newline
character is not written at the end, so don't expect it in the output.

- bpo-44891: Tests were added to clarify :func:`id` is preserved when ``obj
* 1`` is used on :class:`str` and :class:`bytes` objects. Patch by Nikita
Sobolev.

- bpo-44852: Add ability to wholesale silence DeprecationWarnings while
running the regression test suite.

- bpo-40928: Notify users running test_decimal regression tests on macOS of
potential harmless "malloc can't allocate region" messages spewed by
test_decimal.

- bpo-44734: Fixed floating point precision issue in turtle tests.

- bpo-44708: Regression tests, when run with -w, are now re-running only the
affected test methods instead of re-running the entire test file.

- bpo-42095: Added interop tests for Apple plists: generate plist files with
Python plistlib and parse with Apple plutil; and the other way round.

- bpo-44647: Added a permanent Unicode-valued environment variable to
regression tests to ensure they handle this use case in the future. If
your test environment breaks because of that, report a bug to us, and
temporarily set PYTHONREGRTEST_UNICODE_GUARD=0 in your test environment.

- bpo-44515: Adjust recently added contextlib tests to avoid assuming the
use of a refcounted GC

- bpo-44287: Fix asyncio test_popen() of test_windows_utils by using a
longer timeout. Use military grade battle-tested
:data:`test.support.SHORT_TIMEOUT` timeout rather than a hardcoded timeout
of 10 seconds: it's 30 seconds by default, but it is made longer on slow
buildbots. Patch by Victor Stinner.

- bpo-44451: Reset ``DeprecationWarning`` filters in
``test.test_importlib.test_metadata_api.APITests.test_entry_points_by_index``
to avoid ``StopIteration`` error if ``DeprecationWarnings`` are ignored.

- bpo-44363: Account for address sanitizer in test_capi. test_capi now
passes when run GCC address sanitizer.

- bpo-44364: Add non integral tests for :func:`math.sqrt` function.

- bpo-43921: Fix test_ssl.test_wrong_cert_tls13(): use
``suppress_ragged_eofs=False``, since ``read()`` can raise
:exc:`ssl.SSLEOFError` on Windows. Patch by Victor Stinner.

- bpo-43921: Fix test_pha_required_nocert() of test_ssl: catch two more EOF
cases (when the ``recv()`` method returns an empty string). Patch by
Victor Stinner.

- bpo-44131: Add test_frozenmain to test_embed to test the
:c:func:`Py_FrozenMain` C function. Patch by Victor Stinner.

- bpo-31904: Ignore error string case in test_file_not_exists().

- bpo-42083: Add test to check that ``PyStructSequence_NewType`` accepts a
``PyStructSequence_Desc`` with ``doc`` field set to ``NULL``.

- bpo-35753: Fix crash in doctest when doctest parses modules that include
unwrappable functions by skipping those functions.

- bpo-30256: Add test for nested queues when using ``multiprocessing``
shared objects ``AutoProxy[Queue]`` inside ``ListProxy`` and ``DictProxy``

Build
-----

- bpo-45220: Avoid building with the Windows 11 SDK previews automatically.
This may be overridden by setting the ``DefaultWindowsSDKVersion``
environment variable before building.

- bpo-45020: Freeze stdlib modules that are imported during startup. This
provides significant performance improvements to startup. If necessary,
use the previously added "-X frozen_modules=off" commandline option to
force importing the source modules.

- bpo-45188: Windows builds now regenerate frozen modules as the first part
of the build. Previously the regeneration was later in the build, which
would require it to be restarted if any modules had changed.

- bpo-45163: Fixes Haiku platform build.

- bpo-45067: The ncurses function extended_color_content was introduced in
2017

(https://invisible-island.net/ncurses/NEWS.html#index-t20170401). The

ncurses-devel package in CentOS 7 had a older version ncurses resulted in
compilation error. For compiling ncurses with extended color support, we
verify the version of the ncurses library >= 20170401.

- bpo-45019: Generate lines in relevant files for frozen modules. Up until
now each of the files had to be edited manually. This change makes it
easier to add to and modify the frozen modules.

- bpo-44340: Add support for building with clang thin lto via
--with-lto=thin/full. Patch by Dong-hee Na and Brett Holman.

- bpo-44535: Enable building using a Visual Studio 2022 install on Windows.

- bpo-43298: Improved error message when building without a Windows SDK
installed.

- bpo-44381: The Windows build now accepts :envvar:`EnableControlFlowGuard`
set to ``guard`` to enable CFG.

- bpo-41282: Fix broken ``make install`` that caused standard library
extension modules to be unnecessarily and incorrectly rebuilt during the
install phase of cpython.

Windows
-------

- bpo-45375: Fixes an assertion failure due to searching for the standard
library in unnormalised paths.

- bpo-45022: Update Windows release to include libffi 3.4.2

- bpo-45007: Update to OpenSSL 1.1.1l in Windows build

- bpo-44848: Upgrade Windows installer to use SQLite 3.36.0.

- bpo-44572: Avoid consuming standard input in the :mod:`platform` module

- bpo-44582: Accelerate speed of :mod:`mimetypes` initialization using a
native implementation of the registry scan.

- bpo-41299: Fix 16 milliseconds jitter when using timeouts in
:mod:`threading`, such as with :meth:`threading.Lock.acquire` or
:meth:`threading.Condition.wait`.

- bpo-42686: Build :mod:`sqlite3` with math functions enabled. Patch by
Erlend E. Aasland.

- bpo-40263: This is a follow-on bug from
https://bugs.python.org/issue26903. Once that is applied we run into an
off-by-one assertion problem. The assert was not correct.

macOS
-----

- bpo-45007: Update macOS installer builds to use OpenSSL 1.1.1l.

- bpo-34602: When building CPython on macOS with ``./configure
--with-undefined-behavior-sanitizer --with-pydebug``, the stack size is
now quadrupled to allow for the entire test suite to pass.

- bpo-44848: Update macOS installer to use SQLite 3.36.0.

- bpo-44689: :meth:`ctypes.util.find_library` now works correctly on macOS
11 Big Sur even if Python is built on an older version of macOS.
Previously, when built on older macOS systems, ``find_library`` was not
able to find macOS system libraries when running on Big Sur due to
changes in how system libraries are stored.

- bpo-41972: The framework build's user header path in sysconfig is changed
to add a 'pythonX.Y' component to match distutils's behavior.

- bpo-43109: Allow --with-lto configure option to work with Apple-supplied
Xcode or Command Line Tools.

- bpo-34932: Add socket.TCP_KEEPALIVE support for macOS. Patch by Shane
Harvey.

IDLE
----

- bpo-45296: On Windows, change exit/quit message to suggest Ctrl-D, which
works, instead of <Ctrl-Z Return>, which does not work in IDLE.

- bpo-45193: Make completion boxes appear on Ubuntu again.

- bpo-40128: Mostly fix completions on macOS when not using tcl/tk 8.6.11
(as with 3.9). The added update_idletask call should be harmless and
possibly helpful otherwise.

- bpo-33962: Move the indent space setting from the Font tab to the new
Windows tab. Patch by Mark Roseman and Terry Jan Reedy.

- bpo-40468: Split the settings dialog General tab into Windows and Shell/ED
tabs. Move help sources, which extend the Help menu, to the Extensions
tab. Make space for new options and shorten the dialog. The latter makes
the dialog better fit small screens.

- bpo-41611: Avoid uncaught exceptions in
``AutoCompleteWindow.winconfig_event()``.

- bpo-41611: Fix IDLE sometimes freezing upon tab-completion on macOS.

- bpo-44010: Highlight the new :ref:`match <match>` statement's :ref:`soft
keywords <soft-keywords>`: :keyword:`match`, :keyword:`case <match>`, and
:keyword:`_ <wildcard-patterns>`. However, this highlighting is not
perfect and will be incorrect in some rare cases, including some ``_``-s
in ``case`` patterns.

- bpo-44026: Include interpreter's typo fix suggestions in message line for
NameErrors and AttributeErrors. Patch by E. Paine.

Tools/Demos
-----------

- bpo-44786: Fix a warning in regular expression in the c-analyzer script.

- bpo-44967: pydoc now returns a non-zero status code when a module cannot
be found.

- bpo-44978: Allow the Argument Clinic tool to handle ``__complex__``
special methods.

- bpo-43425: Removed the 'test2to3' demo project that demonstrated using
lib2to3 to support Python 2.x and Python 3.x from a single source in a
distutils package. Patch by Dong-hee Na

- bpo-44074: Make patchcheck automatically detect the correct base branch
name (previously it was hardcoded to 'master')

- bpo-20291: Added support for variadic positional parameters in Argument
Clinic.

C API
-----

- bpo-41710: The PyThread_acquire_lock_timed() function now clamps the
timeout if it is too large, rather than aborting the process. Patch by
Victor Stinner.

- bpo-44687: :meth:`BufferedReader.peek` no longer raises :exc:`ValueError`
when the entire file has already been buffered.

- bpo-45116: Add the :c:macro:`Py_ALWAYS_INLINE` macro to ask the compiler
to always inline a static inline function. The compiler can ignore it and
decides to not inline the function. Patch by Victor Stinner.

- bpo-45094: Add the :c:macro:`Py_NO_INLINE` macro to disable inlining on a
function. Patch by Victor Stinner.

- bpo-45061: Add a deallocator to the :class:`bool` type to detect refcount
bugs in C extensions which call ``Py_DECREF(Py_True);`` or
``Py_DECREF(Py_False);`` by mistake. Patch by Victor Stinner.

- bpo-42035: Add a new :c:func:`PyType_GetQualName` function to get type's
qualified name.

- bpo-41103: Reverts removal of the old buffer protocol because they are
part of stable ABI.

- bpo-44751: Remove ``crypt.h`` include from the public ``Python.h`` header.

- bpo-42747: The ``Py_TPFLAGS_HAVE_VERSION_TAG`` type flag now does nothing.
The ``Py_TPFLAGS_HAVE_AM_SEND`` flag (which was added in 3.10) is removed.
Both were unnecessary because it is not possible to have type objects with
the relevant fields missing.

- bpo-44530: Added the ``co_qualname`` to the ``PyCodeObject`` structure to
propagate the qualified name from the compiler to code objects.

Patch by Gabriele N. Tornetta

- bpo-44441: :c:func:`Py_RunMain` now resets :c:data:`PyImport_Inittab` to
its initial value at exit. It must be possible to call
:c:func:`PyImport_AppendInittab` or :c:func:`PyImport_ExtendInittab` at
each Python initialization. Patch by Victor Stinner.

- bpo-39947: Remove 4 private trashcan C API functions which were only kept
for the backward compatibility of the stable ABI with Python 3.8 and
older, since the trashcan API was not usable with the limited C API on
Python 3.8 and older. The trashcan API was excluded from the limited C API
in Python 3.9.

Removed functions:

* _PyTrash_deposit_object()
* _PyTrash_destroy_chain()
* _PyTrash_thread_deposit_object()
* _PyTrash_thread_destroy_chain()

The trashcan C API was never usable with the limited C API, since old
trashcan macros accessed directly :c:type:`PyThreadState` members like
``_tstate->trash_delete_nesting``, whereas the :c:type:`PyThreadState`
structure is opaque in the limited C API.

Exclude also the ``PyTrash_UNWIND_LEVEL`` constant from the C API.

Patch by Victor Stinner.

- bpo-40939: Removed documentation for the removed ``PyParser_*`` C API.

- bpo-43795: The list in :ref:`stable-abi-list` now shows the public name
:c:struct:`PyFrameObject` rather than ``_frame``. The non-existing entry
``_node`` no longer appears in the list.

- bpo-44378: :c:func:`Py_IS_TYPE` no longer uses :c:func:`Py_TYPE` to avoid
a compiler warning: no longer cast ``const PyObject*`` to ``PyObject*``.
Patch by Victor Stinner.

- bpo-39573: Convert the :c:func:`Py_TYPE` and :c:func:`Py_SIZE` macros to
static inline functions. The :c:func:`Py_SET_TYPE` and
:c:func:`Py_SET_SIZE` functions must now be used to set an object type and
size. Patch by Victor Stinner.

- bpo-44263: The :c:func:`PyType_Ready` function now raises an error if a
type is defined with the :const:`Py_TPFLAGS_HAVE_GC` flag set but has no
traverse function (:c:member:`PyTypeObject.tp_traverse`). Patch by Victor
Stinner.

- bpo-43795: The undocumented function :c:func:`Py_FrozenMain` is removed
from the Limited API.

- bpo-44113: Deprecate the following functions to configure the Python
initialization:

* :c:func:`PySys_AddWarnOptionUnicode`
* :c:func:`PySys_AddWarnOption`
* :c:func:`PySys_AddXOption`
* :c:func:`PySys_HasWarnOptions`
* :c:func:`Py_SetPath`
* :c:func:`Py_SetProgramName`
* :c:func:`Py_SetPythonHome`
* :c:func:`Py_SetStandardStreamEncoding`
* :c:func:`_Py_SetProgramFullPath`

Use the new :c:type:`PyConfig` API of the :ref:`Python Initialization
Configuration <init-config>` instead (:pep:`587`).

- bpo-44094: Remove ``PyErr_SetFromErrnoWithUnicodeFilename()``,
``PyErr_SetFromWindowsErrWithUnicodeFilename()``, and
``PyErr_SetExcFromWindowsErrWithUnicodeFilename()``. They are not
documented and have been deprecated since Python 3.3.

- bpo-43795: :c:func:`PyCodec_Unregister` is now properly exported as a
function in the Windows Stable ABI DLL.

- bpo-44029: Remove deprecated ``Py_UNICODE`` APIs: ``PyUnicode_Encode``,
``PyUnicode_EncodeUTF7``, ``PyUnicode_EncodeUTF8``,
``PyUnicode_EncodeUTF16``, ``PyUnicode_EncodeUTF32``,
``PyUnicode_EncodeLatin1``, ``PyUnicode_EncodeMBCS``,
``PyUnicode_EncodeDecimal``, ``PyUnicode_EncodeRawUnicodeEscape``,
``PyUnicode_EncodeCharmap``, ``PyUnicode_EncodeUnicodeEscape``,
``PyUnicode_TransformDecimalToASCII``, ``PyUnicode_TranslateCharmap``,
``PyUnicodeEncodeError_Create``, ``PyUnicodeTranslateError_Create``. See
:pep:`393` and :pep:`624` for reference.

- bpo-42035: Add a new :c:func:`PyType_GetName` function to get type's short
name.

What's New in Python 3.10.0 beta 1?
===================================

*Release date: 2021-05-03*

Security
--------

- bpo-43434: Creating :class:`sqlite3.Connection` objects now also produces
``sqlite3.connect`` and ``sqlite3.connect/handle`` :ref:`auditing events
<auditing>`. Previously these events were only produced by
:func:`sqlite3.connect` calls. Patch by Erlend E. Aasland.

- bpo-43998: The :mod:`ssl` module sets more secure cipher suites defaults.
Ciphers without forward secrecy and with SHA-1 MAC are disabled by
default. Security level 2 prohibits weak RSA, DH, and ECC keys with less
than 112 bits of security. :class:`~ssl.SSLContext` defaults to minimum
protocol version TLS 1.2. Settings are based on Hynek Schlawack's
research.

- bpo-43882: The presence of newline or tab characters in parts of a URL
could allow some forms of attacks.

Following the controlling specification for URLs defined by WHATWG
:func:`urllib.parse` now removes ASCII newlines and tabs from URLs,
preventing such attacks.

- bpo-43472: Ensures interpreter-level audit hooks receive the
``cpython.PyInterpreterState_New`` event when called through the
``_xxsubinterpreters`` module.

- bpo-43362: Fix invalid free in _sha3 module. The issue was introduced in
3.10.0a1. Python 3.9 and earlier are not affected.

- bpo-43762: Add audit events for :func:`sqlite3.connect/handle`,
:meth:`sqlite3.Connection.enable_load_extension`, and
:meth:`sqlite3.Connection.load_extension`. Patch by Erlend E. Aasland.

- bpo-43756: Add new audit event ``glob.glob/2`` to incorporate the new
*root_dir* and *dir_fd* arguments added to :func:`glob.glob` and
:func:`glob.iglob`.

- bpo-36384: :mod:`ipaddress` module no longer accepts any leading zeros in
IPv4 address strings. Leading zeros are ambiguous and interpreted as octal
notation by some libraries. For example the legacy function
:func:`socket.inet_aton` treats leading zeros as octal notation. glibc
implementation of modern :func:`~socket.inet_pton` does not accept any
leading zeros. For a while the :mod:`ipaddress` module used to accept
ambiguous leading zeros.

- bpo-43075: Fix Regular Expression Denial of Service (ReDoS) vulnerability
in :class:`urllib.request.AbstractBasicAuthHandler`. The ReDoS-vulnerable
regex has quadratic worst-case complexity and it allows cause a denial of
service when identifying crafted invalid RFCs. This ReDoS issue is on the
client side and needs remote attackers to control the HTTP server.

- bpo-42800: Audit hooks are now fired for frame.f_code, traceback.tb_frame,
and generator code/frame attribute access.

- bpo-37363: Add audit events to the :mod:`http.client` module.

Core and Builtins
-----------------

- bpo-43977: Prevent classes being both a sequence and a mapping when
pattern matching.

- bpo-43977: Use :c:member:`~PyTypeObject.tp_flags` on the class object to
determine if the subject is a sequence or mapping when pattern matching.
Avoids the need to import :mod:`collections.abc` when pattern matching.

- bpo-43892: Restore proper validation of complex literal value patterns
when parsing :keyword:`!match` blocks.

- bpo-43933: Set frame.f_lineno to the line number of the 'with' kweyword
when executing the call to ``__exit__``.

- bpo-43933: If the current position in a frame has no line number then set
the f_lineno attribute to None, instead of -1, to conform to PEP 626. This
should not normally be possible, but might occur in some unusual
circumstances.

- bpo-43963: Importing the :mod:`_signal` module in a subinterpreter has no
longer side effects.

- bpo-42739: The internal representation of line number tables is changed to
not use sentinels, and an explicit length parameter is added to the out of
process API function ``PyLineTable_InitAddressRange``. This makes the
handling of line number tables more robust in some circumstances.

- bpo-43908: Make :mod:`re` types immutable. Patch by Erlend E. Aasland.

- bpo-43908: Make the :class:`array.array` type immutable. Patch by Erlend
E. Aasland.

- bpo-43901: Change class and module objects to lazy-create empty
annotations dicts on demand. The annotations dicts are stored in the
object's __dict__ for backwards compatibility.

- bpo-43892: Match patterns now use new dedicated AST nodes (``MatchValue``,
``MatchSingleton``, ``MatchSequence``, ``MatchStar``, ``MatchMapping``,
``MatchClass``) rather than reusing expression AST nodes. ``MatchAs`` and
``MatchOr`` are now defined as pattern nodes rather than as expression
nodes. Patch by Nick Coghlan.

- bpo-42725: Usage of ``await``/``yield``/``yield from`` and named
expressions within an annotation is now forbidden when PEP 563 is
activated.

- bpo-43754: When performing structural pattern matching (:pep:`634`),
captured names are now left unbound until the *entire* pattern has matched
successfully.

- bpo-42737: Annotations for complex targets (everything beside simple
names) no longer cause any runtime effects with ``from __future__ import
annotations``.

- bpo-43914: :exc:`SyntaxError` exceptions raised by the interpreter will
highlight the full error range of the expression that consistutes the
syntax error itself, instead of just where the problem is detected. Patch
by Pablo Galindo.

- bpo-38605: Revert making ``from __future__ import annotations`` the
default. This follows the Steering Council decision to postpone PEP 563
changes to at least Python 3.11. See the original email for more
information regarding the decision:
https://mail.python.org/archives/list/python-dev@python.org/thread/CLVXXPQ2T2LQ5MP2Y53VVQFCXYWQJHKZ/.
Patch by Pablo Galindo.

- bpo-43475: Hashes of NaN values now depend on object identity. Formerly,
they always hashed to 0 even though NaN values are not equal to one
another. Having the same hash for unequal values caused pile-ups in hash
tables.

- bpo-43859: Improve the error message for :exc:`IndentationError`
exceptions. Patch by Pablo Galindo

- bpo-41323: Constant tuple folding in bytecode optimizer now reuses tuple
in constant table.

- bpo-43846: Data stack usage is much reduced for large literal and call
expressions.

- bpo-38530: When printing :exc:`NameError` raised by the interpreter,
:c:func:`PyErr_Display` will offer suggestions of similar variable names
in the function that the exception was raised from. Patch by Pablo Galindo

- bpo-43823: Improve syntax errors for invalid dictionary literals. Patch by
Pablo Galindo.

- bpo-43822: Improve syntax errors in the parser for missing commas between
expressions. Patch by Pablo Galindo.

- bpo-43798: :class:`ast.alias` nodes now include source location metadata
attributes e.g. lineno, col_offset.

- bpo-43797: Improve ``SyntaxError`` error messages for invalid comparisons.
Patch by Pablo Galindo.

- bpo-43760: Move the flag for checking whether tracing is enabled to the C
stack, from the heap. Should speed up dispatch in the interpreter.

- bpo-43682: Static methods (:func:`@staticmethod <staticmethod>`) and class
methods (:func:`@classmethod <classmethod>`) now inherit the method
attributes (``__module__``, ``__name__``, ``__qualname__``, ``__doc__``,
``__annotations__``) and have a new ``__wrapped__`` attribute. Patch by
Victor Stinner.

- bpo-43751: Fixed a bug where ``anext(ait, default)`` would erroneously
return None.

- bpo-42128: :data:`~object.__match_args__` is no longer allowed to be a
list.

- bpo-43683: Add GEN_START opcode. Marks start of generator, including
async, or coroutine and handles sending values to a newly created
generator or coroutine.

- bpo-43105: Importlib now resolves relative paths when creating module spec
objects from file locations.

- bpo-43682: Static methods (:func:`@staticmethod <staticmethod>`) are now
callable as regular functions. Patch by Victor Stinner.

- bpo-42609: Prevented crashes in the AST validator and optimizer when
compiling some absurdly long expressions like ``"+0"*1000000``.
:exc:`RecursionError` is now raised instead.

- bpo-38530: When printing :exc:`AttributeError`, :c:func:`PyErr_Display`
will offer suggestions of similar attribute names in the object that the
exception was raised from. Patch by Pablo Galindo

Library
-------

- bpo-44015: In @dataclass(), raise a TypeError if KW_ONLY is specified more
than once.

- bpo-25478: Added a *total()* method to collections.Counter() to compute
the sum of the counts.

- bpo-43733: Change :class:`netrc.netrc` to use UTF-8 encoding before using
locale encoding.

- bpo-43979: Removed an unnecessary list comprehension before looping from
:func:`urllib.parse.parse_qsl`. Patch by Christoph Zwerschke and Dong-hee
Na.

- bpo-43993: Update bundled pip to 21.1.1.

- bpo-43957: [Enum] Deprecate ``TypeError`` when non-member is used in a
containment check; In 3.12 ``True`` or ``False`` will be returned instead,
and containment will return ``True`` if the value is either a member of
that enum or one of its members' value.

- bpo-42904: For backwards compatibility with previous minor versions of
Python, if :func:`typing.get_type_hints` receives no namespace dictionary
arguments, :func:`typing.get_type_hints` will search through the global
then local namespaces during evaluation of stringized type annotations
(string forward references) inside a class.

- bpo-43945: [Enum] Deprecate non-standard mixin format() behavior: in 3.12
the enum member, not the member's value, will be used for format() calls.

- bpo-41139: Deprecate undocumented ``cgi.log()`` API.

- bpo-43937: Fixed the :mod:`turtle` module working with non-default root
window.

- bpo-43930: Update bundled pip to 21.1 and setuptools to 56.0.0

- bpo-43907: Fix a bug in the pure-Python pickle implementation when using
protocol 5, where bytearray instances that occur several time in the
pickled object graph would incorrectly unpickle into repeated copies of
the bytearray object.

- bpo-43926: In ``importlib.metadata``, provide a uniform interface to
``Description``, allow for any field to be encoded with multiline values,
remove continuation lines from multiline values, and add a ``.json``
property for easy access to the PEP 566 JSON-compatible form. Sync with
``importlib_metadata 4.0``.

- bpo-43920: OpenSSL 3.0.0: :meth:`~ssl.SSLContext.load_verify_locations`
now returns a consistent error message when cadata contains no valid
certificate.

- bpo-43607: :mod:`urllib` can now convert Windows paths with ``\\?\``
prefixes into URL paths.

- bpo-43817: Add :func:`inspect.get_annotations`, which safely computes the
annotations defined on an object. It works around the quirks of accessing
the annotations from various types of objects, and makes very few
assumptions about the object passed in. :func:`inspect.get_annotations`
can also correctly un-stringize stringized annotations.

:func:`inspect.signature`, :func:`inspect.from_callable`, and
:func:`inspect.from_function` now call :func:`inspect.get_annotations` to
retrieve annotations. This means :func:`inspect.signature` and
:func:`inspect.from_callable` can now un-stringize stringized annotations,
too.

- bpo-43284: platform.win32_ver derives the windows version from
sys.getwindowsversion().platform_version which in turn derives the version
from kernel32.dll (which can be of a different version than Windows
itself). Therefore change the platform.win32_ver to determine the version
using the platform module's _syscmd_ver private function to return an
accurate version.

- bpo-42854: The :mod:`ssl` module now uses ``SSL_read_ex`` and
``SSL_write_ex`` internally. The functions support reading and writing of
data larger than 2 GB. Writing zero-length data no longer fails with a
protocol violation error.

- bpo-42333: Port ``_ssl`` extension module to multiphase initialization.

- bpo-43880: :mod:`ssl` now raises DeprecationWarning for OP_NO_SSL/TLS*
options, old TLS versions, old protocols, and other features that have
been deprecated since Python 3.6, 3.7, or OpenSSL 1.1.0.

- bpo-41559: :pep:`612` is now implemented purely in Python; builtin
``types.GenericAlias`` objects no longer include ``typing.ParamSpec`` in
``__parameters__`` (with the exception of ``collections.abc.Callable``\ 's
``GenericAlias``). This means previously invalid uses of ``ParamSpec``
(such as ``list[P]``) which worked in earlier versions of Python 3.10
alpha, will now raise ``TypeError`` during substitution.

- bpo-43867: The :mod:`multiprocessing` ``Server`` class now explicitly
catches :exc:`SystemExit` and closes the client connection in this case.
It happens when the ``Server.serve_client()`` method reaches the end of
file (EOF).

- bpo-40443: Remove unused imports: pyclbr no longer uses copy, and typing
no longer uses ast. Patch by Victor Stinner.

- bpo-43820: Remove an unneeded copy of the namespace passed to
dataclasses.make_dataclass().

- bpo-43787: Add ``__iter__()`` method to :class:`bz2.BZ2File`,
:class:`gzip.GzipFile`, and :class:`lzma.LZMAFile`. It makes iterating
them about 2x faster. Patch by Inada Naoki.

- bpo-43680: Deprecate io.OpenWrapper and _pyio.OpenWrapper: use io.open and
_pyio.open instead. Until Python 3.9, _pyio.open was not a static method
and builtins.open was set to OpenWrapper to not become a bound method when
set to a class variable. _io.open is a built-in function whereas
_pyio.open is a Python function. In Python 3.10, _pyio.open() is now a
static method, and builtins.open() is now io.open().

- bpo-43680: The Python :func:`_pyio.open` function becomes a static method
to behave as :func:`io.open` built-in function: don't become a bound
method when stored as a class variable. It becomes possible since static
methods are now callable in Python 3.10. Moreover,
:func:`_pyio.OpenWrapper` becomes a simple alias to :func:`_pyio.open`.
Patch by Victor Stinner.

- bpo-41515: Fix :exc:`KeyError` raised in :func:`typing.get_type_hints` due
to synthetic modules that don't appear in ``sys.modules``.

- bpo-43776: When :class:`subprocess.Popen` args are provided as a string or
as :class:`pathlib.Path`, the Popen instance repr now shows the right
thing.

- bpo-42248: [Enum] ensure exceptions raised in ``_missing__`` are released

- bpo-43744: fix issue with enum member name matching the start of a private
variable name

- bpo-43772: Fixed the return value of ``TypeVar.__ror__``. Patch by Jelle
Zijlstra.

- bpo-43764: Add match_args parameter to @dataclass decorator to allow
suppression of __match_args__ generation.

- bpo-43799: OpenSSL 3.0.0: define ``OPENSSL_API_COMPAT`` 1.1.1 to suppress
deprecation warnings. Python requires OpenSSL 1.1.1 APIs.

- bpo-43478: Mocks can no longer be used as the specs for other Mocks. As a
result, an already-mocked object cannot have an attribute mocked using
``autospec=True`` or be the subject of a ``create_autospec(...)`` call.
This can uncover bugs in tests since these Mock-derived Mocks will always
pass certain tests (e.g. :func:`isinstance`) and builtin assert functions
(e.g. assert_called_once_with) will unconditionally pass.

- bpo-43794: Add :data:`ssl.OP_IGNORE_UNEXPECTED_EOF` constants (OpenSSL
3.0.0)

- bpo-43785: Improve ``bz2.BZ2File`` performance by removing the RLock from
BZ2File. This makes BZ2File thread unsafe in the face of multiple
simultaneous readers or writers, just like its equivalent classes in
:mod:`gzip` and :mod:`lzma` have always been. Patch by Inada Naoki.

- bpo-43789: OpenSSL 3.0.0: Don't call the password callback function a
second time when first call has signaled an error condition.

- bpo-43788: The header files for :mod:`ssl` error codes are now OpenSSL
version-specific. Exceptions will now show correct reason and library
codes. The ``make_ssl_data.py`` script has been rewritten to use OpenSSL's
text file with error codes.

- bpo-43766: Implement :pep:`647` in the :mod:`typing` module by adding
:data:`TypeGuard`.

- bpo-25264: :func:`os.path.realpath` now accepts a *strict* keyword-only
argument. When set to ``True``, :exc:`OSError` is raised if a path doesn't
exist or a symlink loop is encountered.

- bpo-43780: In ``importlib.metadata``, incorporate changes from
importlib_metadata 3.10: Add mtime-based caching during distribution
discovery. Flagged use of dict result from ``entry_points()`` as
deprecated.

- The ``P.args`` and ``P.kwargs`` attributes of :class:`typing.ParamSpec`
are now instances of the new classes :class:`typing.ParamSpecArgs` and
:class:`typing.ParamSpecKwargs`, which enables a more useful ``repr()``.
Patch by Jelle Zijlstra.

- bpo-43731: Add an ``encoding`` parameter :func:`logging.fileConfig()`.

- bpo-43712: Add ``encoding`` and ``errors`` parameters to
:func:`fileinput.input` and :class:`fileinput.FileInput`.

- bpo-38659: A ``simple_enum`` decorator is added to the ``enum`` module to
convert a normal class into an Enum. ``test_simple_enum`` added to test
simple enums against a corresponding normal Enum. Standard library
modules updated to use ``simple_enum``.

- bpo-43764: Fix an issue where :data:`~object.__match_args__` generation
could fail for some :mod:`dataclasses`.

- bpo-43752: Fix :mod:`sqlite3` regression for zero-sized blobs with
converters, where ``b""`` was returned instead of ``None``. The regression
was introduced by PR 24723. Patch by Erlend E. Aasland.

- bpo-43655: :mod:`tkinter` dialog windows are now recognized as dialogs by
window managers on macOS and X Window.

- bpo-43723: The following ``threading`` methods are now deprecated and
should be replaced:

- ``currentThread`` => :func:`threading.current_thread`

- ``activeCount`` => :func:`threading.active_count`

- ``Condition.notifyAll`` => :meth:`threading.Condition.notify_all`

- ``Event.isSet`` => :meth:`threading.Event.is_set`

- ``Thread.setName`` => :attr:`threading.Thread.name`

- ``thread.getName`` => :attr:`threading.Thread.name`

- ``Thread.isDaemon`` => :attr:`threading.Thread.daemon`

- ``Thread.setDaemon`` => :attr:`threading.Thread.daemon`

Patch by Jelle Zijlstra.

- bpo-2135: Deprecate find_module() and find_loader() implementations in
importlib and zipimport.

- bpo-43534: :func:`turtle.textinput` and :func:`turtle.numinput` create now
a transient window working on behalf of the canvas window.

- bpo-43532: Add the ability to specify keyword-only fields to dataclasses.
These fields will become keyword-only arguments to the generated __init__.

- bpo-43522: Fix problem with
:attr:`~ssl.SSLContext.hostname_checks_common_name`. OpenSSL does not copy
hostflags from *struct SSL_CTX* to *struct SSL*.

- bpo-8978: Improve error message for :func:`tarfile.open` when :mod:`lzma`
/ :mod:`bz2` are unavailable. Patch by Anthony Sottile.

- bpo-42967: Allow :class:`bytes` ``separator`` argument in
``urllib.parse.parse_qs`` and ``urllib.parse.parse_qsl`` when parsing
:class:`str` query strings. Previously, this raised a ``TypeError``.

- bpo-43296: Improve :mod:`sqlite3` error handling: ``sqlite3_value_blob()``
errors that set ``SQLITE_NOMEM`` now raise :exc:`MemoryError`. Patch by
Erlend E. Aasland.

- bpo-43312: New functions :func:`sysconfig.get_preferred_scheme` and
:func:`sysconfig.get_default_scheme` are added to query a platform for its
preferred "user", "home", and "prefix" (default) scheme names.

- bpo-43265: Improve :meth:`sqlite3.Connection.backup` error handling. The
error message for non-existent target database names is now ``unknown
database <database name>`` instead of ``SQL logic error``. Patch by Erlend
E. Aasland.

- bpo-41282: Install schemes in :mod:`distutils.command.install` are now
loaded from :mod:`sysconfig`.

- bpo-41282: :mod:`distutils.sysconfig` has been merged to :mod:`sysconfig`.

- bpo-43176: Fixed processing of a dataclass that inherits from a frozen
dataclass with no fields. It is now correctly detected as an error.

- bpo-43080: :mod:`pprint` now has support for
:class:`dataclasses.dataclass`. Patch by Lewis Gaul.

- bpo-39950: Add `pathlib.Path.hardlink_to()` method that supersedes
`link_to()`. The new method has the same argument order as `symlink_to()`.

- bpo-42904: :func:`typing.get_type_hints` now checks the local namespace of
a class when evaluating :pep:`563` annotations inside said class.

- bpo-42269: Add ``slots`` parameter to ``dataclasses.dataclass`` decorator
to automatically generate ``__slots__`` for class. Patch provided by Yurii
Karabas.

- bpo-39529: Deprecated use of :func:`asyncio.get_event_loop` without
running event loop. Emit deprecation warning for :mod:`asyncio` functions
which implicitly create a :class:`~asyncio.Future` or
:class:`~asyncio.Task` objects if there is no running event loop and no
explicit *loop* argument is passed: :func:`~asyncio.ensure_future`,
:func:`~asyncio.wrap_future`, :func:`~asyncio.gather`,
:func:`~asyncio.shield`, :func:`~asyncio.as_completed` and constructors of
:class:`~asyncio.Future`, :class:`~asyncio.Task`,
:class:`~asyncio.StreamReader`, :class:`~asyncio.StreamReaderProtocol`.

- bpo-18369: Certificate and PrivateKey classes were added to the ssl
module. Certificates and keys can now be loaded from memory buffer, too.

- bpo-41486: Use a new output buffer management code for :mod:`bz2` /
:mod:`lzma` / :mod:`zlib` modules, and add ``.readall()`` function to
``_compression.DecompressReader`` class. These bring some performance
improvements. Patch by Ma Lin.

- bpo-31870: The :func:`ssl.get_server_certificate` function now has a
*timeout* parameter.

- bpo-41735: Fix thread locks in zlib module may go wrong in rare case.
Patch by Ma Lin.

- bpo-36470: Fix dataclasses with ``InitVar``\s and
:func:`~dataclasses.replace()`. Patch by Claudiu Popa.

- bpo-40849: Expose X509_V_FLAG_PARTIAL_CHAIN ssl flag

- bpo-35114: :func:`ssl.RAND_status` now returns a boolean value (as
documented) instead of ``1`` or ``0``.

- bpo-39906: :meth:`pathlib.Path.stat` and :meth:`~pathlib.Path.chmod` now
accept a *follow_symlinks* keyword-only argument for consistency with
corresponding functions in the :mod:`os` module.

- bpo-39899: :func:`os.path.expanduser()` now refuses to guess Windows home
directories if the basename of current user's home directory does not
match their username.

:meth:`pathlib.Path.expanduser()` and :meth:`~pathlib.Path.home()` now
consistently raise :exc:`RuntimeError` exception when a home directory
cannot be resolved. Previously a :exc:`KeyError` exception could be raised
on Windows when the ``"USERNAME"`` environment variable was unset.

- bpo-36076: Added SNI support to :func:`ssl.get_server_certificate`.

- bpo-38490: Covariance, Pearson's correlation, and simple linear regression
functionality was added to statistics module. Patch by Tymoteusz Wołodźko.

- bpo-33731: Provide a locale.localize() function, which converts a
normalized number string into a locale format.

- bpo-32745: Fix a regression in the handling of ctypes'
:data:`ctypes.c_wchar_p` type: embedded null characters would cause a
:exc:`ValueError` to be raised. Patch by Zackery Spytz.

Documentation
-------------

- bpo-43987: Add "Annotations Best Practices" document as a new HOWTO.

- bpo-43977: Document the new :const:`Py_TPFLAGS_MAPPING` and
:const:`Py_TPFLAGS_SEQUENCE` type flags.

- bpo-43959: The documentation on the PyContextVar C-API was clarified.

- bpo-43938: Update dataclasses documentation to express that
FrozenInstanceError is derived from AttributeError.

- bpo-43778: Fix the Sphinx glossary_search extension: create the _static/
sub-directory if it doesn't exist.

- bpo-43755: Update documentation to reflect that unparenthesized lambda
expressions can no longer be the expression part in an ``if`` clause in
comprehensions and generator expressions since Python 3.9.

- bpo-43739: Fixing the example code in Doc/extending/extending.rst to
declare and initialize the pmodule variable to be of the right type.

Tests
-----

- bpo-43961: Fix test_logging.test_namer_rotator_inheritance() on Windows:
use :func:`os.replace` rather than :func:`os.rename`. Patch by Victor
Stinner.

- bpo-43842: Fix a race condition in the SMTP test of test_logging. Don't
close a file descriptor (socket) from a different thread while
asyncore.loop() is polling the file descriptor. Patch by Victor Stinner.

- bpo-43843: :mod:`test.libregrtest` now marks a test as ENV_CHANGED
(altered the execution environment) if a thread raises an exception but
does not catch it. It sets a hook on :func:`threading.excepthook`. Use
``--fail-env-changed`` option to mark the test as failed. Patch by Victor
Stinner.

- bpo-43811: Tests multiple OpenSSL versions on GitHub Actions. Use ccache
to speed up testing.

- bpo-43791: OpenSSL 3.0.0: Disable testing of legacy protocols TLS 1.0 and
1.1. Tests are failing with TLSV1_ALERT_INTERNAL_ERROR.

Build
-----

- bpo-43567: Improved generated code refresh (AST/tokens/opcodes/keywords)
on Windows.

- bpo-43669: Implement :pep:`644`. Python now requires OpenSSL 1.1.1 or
newer.

Windows
-------

- bpo-35306: Adds additional arguments to :func:`os.startfile` function.

- bpo-43538: Avoid raising errors from :meth:`pathlib.Path.exists()` when
passed an invalid filename.

- bpo-38822: Fixed :func:`os.stat` failing on inaccessible directories with
a trailing slash, rather than falling back to the parent directory's
metadata. This implicitly affected :func:`os.path.exists` and
:func:`os.path.isdir`.

- bpo-26227: Fixed decoding of host names in :func:`socket.gethostbyaddr`
and :func:`socket.gethostbyname_ex`.

- bpo-40432: Updated pegen regeneration script on Windows to find and use
Python 3.8 or higher. Prior to this, pegen regeneration already required
3.8 or higher, but the script may have used lower versions of Python.

- bpo-43745: Actually updates Windows release to OpenSSL 1.1.1k. Earlier
releases were mislabelled and actually included 1.1.1i again.

- bpo-43652: Update Tcl and Tk to 8.6.11 in Windows installer.

- bpo-43492: Upgrade Windows installer to use SQLite 3.35.5.

- bpo-30555: Fix ``WindowsConsoleIO`` errors in the presence of fd
redirection. Patch by Segev Finer.

macOS
-----

- bpo-42119: Fix check for macOS SDK paths when building Python. Narrow
search to match contents of SDKs, namely only files in
``/System/Library``, ``/System/IOSSupport``, and ``/usr`` other than
``/usr/local``. Previously, anything under ``/System`` was assumed to be
in an SDK which causes problems with the new file system layout in 10.15+
where user file systems may appear to be mounted under ``/System``. Paths
in ``/Library`` were also incorrectly treated as SDK locations.

- bpo-43568: Drop support for MACOSX_DEPLOYMENT_TARGET < 10.3

- bpo-44009: Provide "python3.x-intel64" executable to allow reliably
forcing macOS universal2 framework builds to run under Rosetta 2 Intel-64
emulation on Apple Silicon Macs. This can be useful for testing or when
universal2 wheels are not yet available.

- bpo-43851: Build SQLite with ``SQLITE_OMIT_AUTOINIT`` on macOS. Patch by
Erlend E. Aasland.

- bpo-43492: Update macOS installer to use SQLite 3.35.4.

- bpo-42235: ``Mac/BuildScript/build-installer.py`` will now use
"--enable-optimizations" and ``--with-lto`` when building on macOS 10.15
or later.

IDLE
----

- bpo-37903: Add mouse actions to the shell sidebar. Left click and
optional drag selects one or more lines, as with the editor line number
sidebar. Right click after selecting raises a context menu with 'copy
with prompts'. This zips together prompts from the sidebar with lines
from the selected text.

- bpo-43981: Fix reference leak in test_sidebar and test_squeezer. Patches
by Terry Jan Reedy and Pablo Galindo

- bpo-37892: Indent IDLE Shell input with spaces instead of tabs

- bpo-43655: IDLE dialog windows are now recognized as dialogs by window
managers on macOS and X Window.

- bpo-37903: IDLE's shell now shows prompts in a separate side-bar.

C API
-----

- bpo-43916: Add a new :c:data:`Py_TPFLAGS_DISALLOW_INSTANTIATION` type flag
to disallow creating type instances. Patch by Victor Stinner.

- bpo-43774: Remove the now unused ``PYMALLOC_DEBUG`` macro. Debug hooks on
memory allocators are now installed by default if Python is built in debug
mode (if ``Py_DEBUG`` macro is defined). Moreover, they can now be used on
Python build in release mode (ex: using ``PYTHONMALLOC=debug`` environment
variable).

- bpo-43962: _PyInterpreterState_IDIncref() now calls
_PyInterpreterState_IDInitref() and always increments id_refcount.
Previously, calling _xxsubinterpreters.get_current() could create an
id_refcount inconsistency when a _xxsubinterpreters.InterpreterID object
was deallocated. Patch by Victor Stinner.

- bpo-28254: Add new C-API functions to control the state of the garbage
collector: :c:func:`PyGC_Enable()`, :c:func:`PyGC_Disable()`,
:c:func:`PyGC_IsEnabled()`, corresponding to the functions in the
:mod:`gc` module.

- bpo-43908: Introduce :const:`Py_TPFLAGS_IMMUTABLETYPE` flag for immutable
type objects, and modify :c:func:`PyType_Ready` to set it for static
types. Patch by Erlend E. Aasland.

- bpo-43795: :c:func:`PyMem_Calloc` is now available in the limited C API
(``Py_LIMITED_API``).

- bpo-43868: :c:func:`PyOS_ReadlineFunctionPointer` is no longer exported by
limited C API headers and by ``python3.dll`` on Windows. Like any function
that takes ``FILE*``, it is not part of the stable ABI.

- bpo-43795: Stable ABI and limited API definitions are generated from a
central manifest (:pep:`652`).

- bpo-43753: Add the :c:func:`Py_Is(x, y) <Py_Is>` function to test if the
*x* object is the *y* object, the same as ``x is y`` in Python. Add also
the :c:func:`Py_IsNone`, :c:func:`Py_IsTrue`, :c:func:`Py_IsFalse`
functions to test if an object is, respectively, the ``None`` singleton,
the ``True`` singleton or the ``False`` singleton. Patch by Victor
Stinner.

What's New in Python 3.10.0 alpha 7?
====================================

*Release date: 2021-04-05*

Security
--------

- bpo-42988: CVE-2021-3426: Remove the ``getfile`` feature of the
:mod:`pydoc` module which could be abused to read arbitrary files on the
disk (directory traversal vulnerability). Moreover, even source code of
Python modules can contain sensitive data like passwords. Vulnerability
reported by David Schwörer.

- bpo-43285: :mod:`ftplib` no longer trusts the IP address value returned
from the server in response to the PASV command by default. This prevents
a malicious FTP server from using the response to probe IPv4 address and
port combinations on the client network.

Code that requires the former vulnerable behavior may set a
``trust_server_pasv_ipv4_address`` attribute on their :class:`ftplib.FTP`
instances to ``True`` to re-enable it.

- bpo-43439: Add audit hooks for :func:`gc.get_objects`,
:func:`gc.get_referrers` and :func:`gc.get_referents`. Patch by Pablo
Galindo.

Core and Builtins
-----------------

- bpo-27129: Update CPython bytecode magic number.

- bpo-43672: Raise ImportWarning when calling find_loader().

- bpo-43660: Fix crash that happens when replacing ``sys.stderr`` with a
callable that can remove the object while an exception is being printed.
Patch by Pablo Galindo.

- bpo-27129: The bytecode interpreter uses instruction, rather byte, offsets
internally. This reduces the number of EXTENDED_ARG instructions needed
and streamlines instruction dispatch a bit.

- bpo-40645: Fix reference leak in the :mod:`_hashopenssl` extension. Patch
by Pablo Galindo.

- bpo-42134: Calls to find_module() by the import system now raise
ImportWarning.

- bpo-41064: Improve the syntax error for invalid usage of double starred
elements ('**') in f-strings. Patch by Pablo Galindo.

- bpo-43575: Speed up calls to ``map()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-42137: The import system now prefers using ``__spec__`` for
``ModuleType.__repr__`` over ``module_repr()``.

- bpo-43452: Added micro-optimizations to ``_PyType_Lookup()`` to improve
cache lookup performance in the common case of cache hits.

- bpo-43555: Report the column offset for :exc:`SyntaxError` for invalid
line continuation characters. Patch by Pablo Galindo.

- bpo-43517: Fix misdetection of circular imports when using ``from pkg.mod
import attr``, which caused false positives in non-trivial multi-threaded
code.

- bpo-43497: Emit SyntaxWarnings for assertions with tuple constants, this
is a regression introduced in python3.7

- bpo-39316: Tracing now has correct line numbers for attribute accesses
when the attribute is on a different line from the object. Improves
debugging and profiling for multi-line method chains.

- bpo-35883: Python no longer fails at startup with a fatal error if a
command line argument contains an invalid Unicode character. The
:c:func:`Py_DecodeLocale` function now escapes byte sequences which would
be decoded as Unicode characters outside the [U+0000; U+10ffff] range.

- bpo-43410: Fix a bug that was causing the parser to crash when emitting
syntax errors when reading input from stdin. Patch by Pablo Galindo

- bpo-43406: Fix a possible race condition where ``PyErr_CheckSignals``
tries to execute a non-Python signal handler.

- bpo-42128: Add ``__match_args__`` to :c:type:`structsequence` based
classes. Patch by Pablo Galindo.

- bpo-43390: CPython now sets the ``SA_ONSTACK`` flag in ``PyOS_setsig`` for
the VM's default signal handlers. This is friendlier to other in-process
code that an extension module or embedding use could pull in (such as
Golang's cgo) where tiny thread stacks are the norm and ``sigaltstack()``
has been used to provide for signal handlers. This is a no-op change for
the vast majority of processes that don't use sigaltstack.

- bpo-43287: Speed up calls to ``filter()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-37448: Add a radix tree based memory map to track in-use obmalloc
arenas. Use to replace the old implementation of address_in_range(). The
radix tree approach makes it easy to increase pool sizes beyond the OS
page size. Boosting the pool and arena size allows obmalloc to handle a
significantly higher percentage of requests from its ultra-fast paths.

It also has the advantage of eliminating the memory unsanitary behavior of
the previous address_in_range(). The old address_in_range() was marked
with the annotations _Py_NO_SANITIZE_ADDRESS, _Py_NO_SANITIZE_THREAD, and
_Py_NO_SANITIZE_MEMORY. Those annotations are no longer needed.

To disable the radix tree map, set a preprocessor flag as follows:
`-DWITH_PYMALLOC_RADIX_TREE=0`.

Co-authored-by: Tim Peters <tim.peters@gmail.com>

- bpo-29988: Only handle asynchronous exceptions and requests to drop the
GIL when returning from a call or on the back edges of loops. Makes sure
that :meth:`__exit__` is always called in with statements, even for
interrupts.

Library
-------

- bpo-43720: Document various stdlib deprecations in imp, pkgutil, and
importlib.util for removal in Python 3.12.

- bpo-43433: :class:`xmlrpc.client.ServerProxy` no longer ignores query and
fragment in the URL of the server.

- bpo-31956: The :meth:`~array.array.index` method of :class:`array.array`
now has optional *start* and *stop* parameters.

- bpo-40066: Enum: adjust ``repr()`` to show only enum and member name (not
value, nor angle brackets) and ``str()`` to show only member name. Update
and improve documentation to match.

- bpo-42136: Deprecate all module_repr() methods found in importlib as their
use is being phased out by Python 3.12.

- bpo-35930: Raising an exception raised in a "future" instance will create
reference cycles.

- bpo-41369: Finish updating the vendored libmpdec to version 2.5.1. Patch
by Stefan Krah.

- bpo-43422: Revert the _decimal C API which was added in bpo-41324.

- bpo-43577: Fix deadlock when using :class:`ssl.SSLContext` debug callback
with :meth:`ssl.SSLContext.sni_callback`.

- bpo-43571: It's now possible to create MPTCP sockets with IPPROTO_MPTCP

- bpo-43542: ``image/heic`` and ``image/heif`` were added to
:mod:`mimetypes`.

- bpo-40645: The :mod:`hmac` module now uses OpenSSL's HMAC implementation
when digestmod argument is a hash name or builtin hash function.

- bpo-43510: Implement :pep:`597`: Add ``EncodingWarning`` warning, ``-X
warn_default_encoding`` option, :envvar:`PYTHONWARNDEFAULTENCODING`
environment variable and ``encoding="locale"`` argument value.

- bpo-43521: ``ast.unparse`` can now render NaNs and empty sets.

- bpo-42914: :func:`pprint.pprint` gains a new boolean
``underscore_numbers`` optional argument to emit integers with thousands
separated by an underscore character for improved readability (for example
``1_000_000`` instead of ``1000000``).

- bpo-41361: :meth:`~collections.deque.rotate` calls are now slightly faster
due to faster argument parsing.

- bpo-43423: :func:`subprocess.communicate` no longer raises an IndexError
when there is an empty stdout or stderr IO buffer during a timeout on
Windows.

- bpo-27820: Fixed long-standing bug of smtplib.SMTP where doing AUTH LOGIN
with initial_response_ok=False will fail.

The cause is that SMTP.auth_login _always_ returns a password if provided
with a challenge string, thus non-compliant with the standard for AUTH
LOGIN.

Also fixes bug with the test for smtpd.

- bpo-43445: Add frozen modules to :data:`sys.stdlib_module_names`. For
example, add ``"_frozen_importlib"`` and ``"_frozen_importlib_external"``
names.

- bpo-43245: Add keyword arguments support to ``ChainMap.new_child()``.

- bpo-29982: Add optional parameter *ignore_cleanup_errors* to
:func:`tempfile.TemporaryDirectory` and allow multiple :func:`cleanup`
attempts. Contributed by C.A.M. Gerlach.

- bpo-43428: Include changes from `importlib_metadata 3.7
<https://importlib-metadata.readthedocs.io/en/latest/history.html#v3-7-0>`_:

Performance enhancements to distribution discovery.

``entry_points`` only returns unique distributions.

Introduces new ``EntryPoints`` object for containing a set of entry points
with convenience methods for selecting entry points by group or name.
``entry_points`` now returns this object if selection parameters are
supplied but continues to return a dict object for compatibility. Users
are encouraged to rely on the selection interface. The dict object result
is likely to be deprecated in the future.

Added packages_distributions function to return a mapping of packages to
the distributions that provide them.

- bpo-43332: Improves the networking efficiency of :mod:`http.client` when
using a proxy via :meth:`~HTTPConnection.set_tunnel`. Fewer small send
calls are made during connection setup.

- bpo-43420: Improve performance of :class:`fractions.Fraction` arithmetics
for large components. Contributed by Sergey B. Kirpichev.

- bpo-43356: Allow passing a signal number to ``_thread.interrupt_main()``.

- bpo-43399: Fix ``ElementTree.extend`` not working on iterators when using
the Python implementation

- bpo-43369: Improve :mod:`sqlite3` error handling: If
``sqlite3_column_text()`` and ``sqlite3_column_blob()`` set
``SQLITE_NOMEM``, :exc:`MemoryError` is now raised. Patch by Erlend E.
Aasland.

- bpo-43368: Fix a regression introduced in PR 24562, where an empty
bytestring was fetched as ``None`` instead of ``b''`` in :mod:`sqlite3`.
Patch by Mariusz Felisiak.

- bpo-41282: Fixed stacklevel of ``DeprecationWarning`` emitted from
``import distutils``.

- bpo-42129: ``importlib.resources`` now honors namespace packages, merging
resources from each location in the namespace as introduced in
``importlib_resources`` 3.2 and including incidental changes through
5.0.3.

- bpo-43295: :meth:`datetime.datetime.strptime` now raises ``ValueError``
instead of ``IndexError`` when matching ``'z'`` with the ``%z`` format
specifier.

- bpo-43125: Return empty string if base64mime.body_encode receive empty
bytes

- bpo-43084: :func:`curses.window.enclose` returns now ``True`` or ``False``
(as was documented) instead of ``1`` or ``0``.

- bpo-42994: Add MIME types for opus, AAC, 3gpp and 3gpp2

- bpo-14678: Add an invalidate_caches() method to the zipimport.zipimporter
class to support importlib.invalidate_caches(). Patch by Desmond Cheong.

- bpo-42782: Fail fast in :func:`shutil.move()` to avoid creating
destination directories on failure.

- bpo-40066: Enum's `repr()` and `str()` have changed: `repr()` is now
*EnumClass.MemberName* and `str()` is *MemberName*. Additionally, stdlib
Enum's whose contents are available as module attributes, such as
`RegexFlag.IGNORECASE`, have their `repr()` as *module.name*, e.g.
`re.IGNORECASE`.

- bpo-26053: Fixed bug where the :mod:`pdb` interactive run command echoed
the args from the shell command line, even if those have been overridden
at the pdb prompt.

- bpo-24160: Fixed bug where breakpoints did not persist across multiple
debugger sessions in :mod:`pdb`'s interactive mode.

- bpo-40701: When the :data:`tempfile.tempdir` global variable is set to a
value of type bytes, it is now handled consistently. Previously
exceptions could be raised from some tempfile APIs when the directory did
not already exist in this situation. Also ensures that the
:func:`tempfile.gettempdir()` and :func:`tempfile.gettempdirb()` functions
*always* return ``str`` and ``bytes`` respectively.

- bpo-39342: Expose ``X509_V_FLAG_ALLOW_PROXY_CERTS`` as
:data:`~ssl.VERIFY_ALLOW_PROXY_CERTS` to allow proxy certificate
validation as explained in
https://www.openssl.org/docs/man1.1.1/man7/proxy-certificates.html.

- bpo-31861: Add builtins.aiter and builtins.anext. Patch by Joshua Bronson
(@jab), Daniel Pope (@lordmauve), and Justin Wang (@justin39).

Documentation
-------------

- bpo-43199: Answer "Why is there no goto?" in the Design and History FAQ.

- bpo-43407: Clarified that a result from :func:`time.monotonic`,
:func:`time.perf_counter`, :func:`time.process_time`, or
:func:`time.thread_time` can be compared with the result from any
following call to the same function - not just the next immediate call.

- bpo-43354: Fix type documentation for ``Fault.faultCode``; the type has to
be ``int`` instead of ``str``.

- bpo-41933: Clarified wording of s * n in the Common Sequence Operations

Tests
-----

- bpo-37945: Fix test_getsetlocale_issue1813() of test_locale: skip the test
if ``setlocale()`` fails. Patch by Victor Stinner.

- bpo-41561: Add workaround for Ubuntu's custom OpenSSL security level
policy.

Build
-----

- bpo-43179: Introduce and correctly use ALIGNOF_X in place of SIZEOF_X for
alignment-related code in optimized string routines. Patch by Jessica
Clarke.

- bpo-43631: Update macOS, Windows, and CI to OpenSSL 1.1.1k.

- bpo-43617: Improve configure.ac: Check for presence of autoconf-archive
package and remove our copies of M4 macros.

- bpo-43466: The ``configure`` script now supports ``--with-openssl-rpath``
option.

- bpo-43372: Use ``_freeze_importlib`` to generate code for the
``__hello__`` module. This approach ensures the code matches the
interpreter version. Previously, PYTHON_FOR_REGEN was used to generate
the code, which might be wrong. The marshal format for code objects has
changed with bpo-42246, commit 877df851. Update the code and the expected
code sizes in ctypes test_frozentable.

Windows
-------

- bpo-43440: Build :mod:`sqlite3` with the ``R*Tree`` module enabled. Patch
by Erlend E. Aasland.

IDLE
----

- bpo-42225: Document that IDLE can fail on Unix either from misconfigured
IP masquerade rules or failure displaying complex colored (non-ascii)
characters.

C API
-----

- bpo-43688: The limited C API is now supported if Python is built in debug
mode (if the ``Py_DEBUG`` macro is defined). In the limited C API, the
:c:func:`Py_INCREF` and :c:func:`Py_DECREF` functions are now implemented
as opaque function calls, rather than accessing directly the
:c:member:`PyObject.ob_refcnt` member, if Python is built in debug mode
and the ``Py_LIMITED_API`` macro targets Python 3.10 or newer. It became
possible to support the limited C API in debug mode because the
:c:type:`PyObject` structure is the same in release and debug mode since
Python 3.8 (see :issue:`36465`).

The limited C API is still not supported in the ``--with-trace-refs``
special build (``Py_TRACE_REFS`` macro).

Patch by Victor Stinner.

- bpo-43244: Remove the ``pyarena.h`` header file with functions:

* ``PyArena_New()``
* ``PyArena_Free()``
* ``PyArena_Malloc()``
* ``PyArena_AddPyObject()``

These functions were undocumented, excluded from the limited C API, and
were only used internally by the compiler. Patch by Victor Stinner.

- bpo-43244: Remove the compiler and parser functions using ``struct _mod``
type, because the public AST C API was removed:

* ``PyAST_Compile()``
* ``PyAST_CompileEx()``
* ``PyAST_CompileObject()``
* ``PyFuture_FromAST()``
* ``PyFuture_FromASTObject()``
* ``PyParser_ASTFromFile()``
* ``PyParser_ASTFromFileObject()``
* ``PyParser_ASTFromFilename()``
* ``PyParser_ASTFromString()``
* ``PyParser_ASTFromStringObject()``

These functions were undocumented and excluded from the limited C API.
Patch by Victor Stinner.

- bpo-43244: Remove ``ast.h``, ``asdl.h``, and ``Python-ast.h`` header
files. These functions were undocumented and excluded from the limited C
API. Most names defined by these header files were not prefixed by ``Py``
and so could create names conflicts. For example, ``Python-ast.h`` defined
a ``Yield`` macro which was conflict with the ``Yield`` name used by the
Windows ``<winbase.h>`` header. Use the Python :mod:`ast` module instead.
Patch by Victor Stinner.

- bpo-43541: Fix a ``PyEval_EvalCodeEx()`` regression: fix reference
counting on builtins. Patch by Victor Stinner.

- bpo-43244: Remove the ``symtable.h`` header file and the undocumented
functions:

* ``PyST_GetScope()``
* ``PySymtable_Build()``
* ``PySymtable_BuildObject()``
* ``PySymtable_Free()``
* ``Py_SymtableString()``
* ``Py_SymtableStringObject()``

The ``Py_SymtableString()`` function was part the stable ABI by mistake
but it could not be used, because the ``symtable.h`` header file was
excluded from the limited C API.

The Python :mod:`symtable` module remains available and is unchanged.

Patch by Victor Stinner.

- bpo-43244: Remove the ``PyAST_Validate()`` function. It is no longer
possible to build a AST object (``mod_ty`` type) with the public C API.
The function was already excluded from the limited C API (:pep:`384`).
Patch by Victor Stinner.

What's New in Python 3.10.0 alpha 6?
====================================

*Release date: 2021-03-01*

Security
--------

- bpo-42967: Fix web cache poisoning vulnerability by defaulting the query
args separator to ``&``, and allowing the user to choose a custom
separator.

Core and Builtins
-----------------

- bpo-43321: Fix ``SystemError`` raised when ``PyArg_Parse*()`` is used with
``#`` but without ``PY_SSIZE_T_CLEAN`` defined.

- bpo-36346: ``PyArg_Parse*()`` functions now emits ``DeprecationWarning``
when ``u`` or ``Z`` format is used. See :pep:`623` for detail.

- bpo-43277: Add a new :c:func:`PySet_CheckExact` function to the C-API to
check if an object is an instance of :class:`set` but not an instance of a
subtype. Patch by Pablo Galindo.

- bpo-42990: The :data:`types.FunctionType` constructor now inherits the
current builtins if the *globals* dictionary has no ``"__builtins__"``
key, rather than using ``{"None": None}`` as builtins: same behavior as
:func:`eval` and :func:`exec` functions. Defining a function with ``def
function(...): ...`` in Python is not affected, globals cannot be
overridden with this syntax: it also inherits the current builtins. Patch
by Victor Stinner.

- bpo-42990: Functions have a new ``__builtins__`` attribute which is used
to look for builtin symbols when a function is executed, instead of
looking into ``__globals__['__builtins__']``. Patch by Mark Shannon and
Victor Stinner.

- bpo-43149: Improve the error message in the parser for exception groups
without parentheses. Patch by Pablo Galindo.

- bpo-43121: Fixed an incorrect :exc:`SyntaxError` message for missing comma
in literals. Patch by Pablo Galindo.

- bpo-42819: :mod:`readline`: Explicitly disable bracketed paste in the
interactive interpreter, even if it's set in the inputrc, is enabled by
default (eg GNU Readline 8.1), or a user calls
``readline.read_init_file()``. The Python REPL has not implemented
bracketed paste support. Also, bracketed mode writes the ``"\x1b[?2004h"``
escape sequence into stdout which causes test failures in applications
that don't support it. It can still be explicitly enabled by calling
``readline.parse_and_bind("set enable-bracketed-paste on")``. Patch by
Dustin Rodrigues.

- bpo-42808: Simple calls to ``type(object)`` are now faster due to the
``vectorcall`` calling convention. Patch by Dennis Sweeney.

- bpo-42217: Make the compiler merges same co_code and co_linetable objects
in a module like already did for co_consts.

- bpo-41972: Substring search functions such as ``str1 in str2`` and
``str2.find(str1)`` now sometimes use the "Two-Way" string comparison
algorithm to avoid quadratic behavior on long strings.

- bpo-42128: Implement :pep:`634` (structural pattern matching). Patch by
Brandt Bucher.

- bpo-40692: In the :class:`concurrent.futures.ProcessPoolExecutor`,
validate that :func:`multiprocess.synchronize` is available on a given
platform and rely on that check in the :mod:`concurrent.futures` test
suite so we can run tests that are unrelated to
:class:`ProcessPoolExecutor` on those platforms.

- bpo-38302: If :func:`object.__ipow__` returns :const:`NotImplemented`, the
operator will correctly fall back to :func:`object.__pow__` and
:func:`object.__rpow__` as expected.

Library
-------

- bpo-43316: The ``python -m gzip`` command line application now properly
fails when detecting an unsupported extension. It exits with a non-zero
exit code and prints an error message to stderr.

- bpo-43317: Set the chunk size for the ``gzip`` module main function to
io.DEFAULT_BUFFER_SIZE. This is slightly faster than the 1024 bytes
constant that was used previously.

- bpo-43146: Handle None in single-arg versions of
:func:`~traceback.print_exception` and
:func:`~traceback.format_exception`.

- bpo-43260: Fix TextIOWrapper can not flush internal buffer forever after
very large text is written.

- bpo-43258: Prevent needless allocation of :mod:`sqlite3` aggregate
function context when no rows match an aggregate query. Patch by Erlend E.
Aasland.

- bpo-43251: Improve :mod:`sqlite3` error handling:
``sqlite3_column_name()`` failures now result in :exc:`MemoryError`. Patch
by Erlend E. Aasland.

- bpo-40956: Fix segfault in :meth:`sqlite3.Connection.backup` if no
argument was provided. The regression was introduced by PR 23838. Patch by
Erlend E. Aasland.

- bpo-43172: The readline module now passes its tests when built directly
against libedit. Existing irreconcilable API differences remain in
:func:`readline.get_begidx` and :func:`readline.get_endidx` behavior based
on libreadline vs libedit use.

- bpo-43163: Fix a bug in :mod:`codeop` that was causing it to not ask for
more input when multi-line snippets have unclosed parentheses. Patch by
Pablo Galindo

- bpo-43162: deprecate unsupported ability to access enum members as
attributes of other enum members

- bpo-43146: Fix recent regression in None argument handling in
:mod:`~traceback` module functions.

- bpo-43102: The namedtuple __new__ method had its __builtins__ set to None
instead of an actual dictionary. This created problems for introspection
tools.

- bpo-43106: Added :data:`~os.O_EVTONLY`, :data:`~os.O_FSYNC`,
:data:`~os.O_SYMLINK` and :data:`~os.O_NOFOLLOW_ANY` for macOS. Patch by
Dong-hee Na.

- bpo-42960: Adds :data:`resource.RLIMIT_KQUEUES` constant from FreeBSD to
the :mod:`resource` module.

- bpo-42151: Make the pure Python implementation of
:mod:`xml.etree.ElementTree` behave the same as the C implementation
(:mod:`_elementree`) regarding default attribute values (by not setting
``specified_attributes=1``).

- bpo-29753: In ctypes, now packed bitfields are calculated properly and the
first item of packed bitfields is now shrank correctly.

Documentation
-------------

- bpo-27646: Clarify that 'yield from <expr>' works with any iterable, not
just iterators.

- bpo-36346: Update some deprecated unicode APIs which are documented as
"will be removed in 4.0" to "3.12". See :pep:`623` for detail.

Tests
-----

- bpo-43288: Fix test_importlib to correctly skip Unicode file tests if the
filesystem does not support them.

Build
-----

- bpo-43174: Windows build now uses ``/utf-8`` compiler option.

- bpo-43103: Add a new configure ``--without-static-libpython`` option to
not build the ``libpythonMAJOR.MINOR.a`` static library and not install
the ``python.o`` object file.

- bpo-13501: The configure script can now use *libedit* instead of
*readline* with the command line option ``--with-readline=editline``.

- bpo-42603: Make configure script use pkg-config to detect the location of
Tcl/Tk headers and libraries, used to build tkinter.

On macOS, a Tcl/Tk configuration provided by pkg-config will be preferred
over Tcl/Tk frameworks installed in ``/{System/,}Library/Frameworks``. If
both exist and the latter is preferred, the appropriate ``--with-tcltk-*``
configuration options need to be explicitly set.

- bpo-39448: Add the "regen-frozen" makefile target that regenerates the
code for the frozen ``__hello__`` module.

Windows
-------

- bpo-43155: :c:func:`PyCMethod_New` is now present in ``python3.lib``.

macOS
-----

- bpo-41837: Update macOS installer build to use OpenSSL 1.1.1j.

IDLE
----

- bpo-43283: Document why printing to IDLE's Shell is often slower than
printing to a system terminal and that it can be made faster by
pre-formatting a single string before printing.

C API
-----

- bpo-43278: Always put compiler and system information on the first line of
the REPL welcome message.

- bpo-43270: Remove the private ``_PyErr_OCCURRED()`` macro: use the public
:c:func:`PyErr_Occurred` function instead.

- bpo-35134: Move odictobject.h, parser_interface.h, picklebufobject.h,
pydebug.h, and pyfpe.h into the cpython/ directory. They must not be
included directly, as they are already included by Python.h: :ref:`Include
Files <api-includes>`.

- bpo-35134: Move pyarena.h, pyctype.h, and pytime.h into the cpython/
directory. They must not be included directly, as they are already
included by Python.h: :ref:`Include Files <api-includes>`.

- bpo-40170: :c:func:`PyExceptionClass_Name` is now always declared as a
function, in order to hide implementation details. The macro accessed
:c:member:`PyTypeObject.tp_name` directly. Patch by Erlend E. Aasland.

- bpo-43239: The :c:func:`PyCFunction_New` function is now exported in the
ABI when compiled with ``-fvisibility=hidden``.

- bpo-40170: :c:func:`PyIter_Check` is now always declared as a function, in
order to hide implementation details. The macro accessed
:c:member:`PyTypeObject.tp_iternext` directly. Patch by Erlend E. Aasland.

- bpo-40170: Convert :c:func:`PyDescr_IsData` macro to a function to hide
implementation details: The macro accessed
:c:member:`PyTypeObject.tp_descr_set` directly. Patch by Erlend E.
Aasland.

- bpo-43181: Convert :c:func:`PyObject_TypeCheck` macro to a static inline
function. Patch by Erlend E. Aasland.

What's New in Python 3.10.0 alpha 5?
====================================

*Release date: 2021-02-02*

Security
--------

- bpo-42938: Avoid static buffers when computing the repr of
:class:`ctypes.c_double` and :class:`ctypes.c_longdouble` values.

Core and Builtins
-----------------

- bpo-42990: Refactor the ``PyEval_`` family of functions.

* An new function ``_PyEval_Vector`` is added to simplify calls to Python from C.
* ``_PyEval_EvalCodeWithName`` is removed
* ``PyEval_EvalCodeEx`` is retained as part of the API, but is not used internally

- bpo-38631: Replace :c:func:`Py_FatalError` calls in the compiler with
regular :exc:`SystemError` exceptions. Patch by Victor Stinner.

- bpo-42997: Improve error message for missing ":" before blocks. Patch by
Pablo Galindo.

- bpo-43017: Improve error message in the parser when using un-parenthesised
tuples in comprehensions. Patch by Pablo Galindo.

- bpo-42986: Fix parser crash when reporting syntax errors in f-string with
newlines. Patch by Pablo Galindo.

- bpo-40176: Syntax errors for unterminated string literals now point to the
start of the string instead of reporting EOF/EOL.

- bpo-42927: The inline cache for ``LOAD_ATTR`` now also optimizes access to
attributes defined by ``__slots__``. This makes reading such attribute up
to 30% faster.

- bpo-42864: Improve error messages in the parser when parentheses are not
closed. Patch by Pablo Galindo.

- bpo-42924: Fix ``bytearray`` repetition incorrectly copying data from the
start of the buffer, even if the data is offset within the buffer (e.g.
after reassigning a slice at the start of the ``bytearray`` to a shorter
byte string).

- bpo-42882: Fix the :c:func:`_PyUnicode_FromId` function
(_Py_IDENTIFIER(var) API) when :c:func:`Py_Initialize` /
:c:func:`Py_Finalize` is called multiple times: preserve
``_PyRuntime.unicode_ids.next_index`` value.

- bpo-42827: Fix a crash when working out the error line of a
:exc:`SyntaxError` in some multi-line expressions.

- bpo-42823: frame.f_lineno is correct even if frame.f_trace is set to True

- bpo-37324: Remove deprecated aliases to
:ref:`collections-abstract-base-classes` from the :mod:`collections`
module.

- bpo-41994: Fixed possible leak in ``import`` when ``sys.modules`` is not a
``dict``.

- bpo-27772: In string formatting, preceding the *width* field by ``'0'`` no
longer affects the default alignment for strings.

Library
-------

- bpo-43108: Fixed a reference leak in the :mod:`curses` module. Patch by
Pablo Galindo

- bpo-43077: Update the bundled pip to 21.0.1 and setuptools to 52.0.0.

- bpo-41282: Deprecate ``distutils`` in documentation and add warning on
import.

- bpo-43014: Improve performance of :mod:`tokenize` by 20-30%. Patch by
Anthony Sottile.

- bpo-42323: Fix :func:`math.nextafter` for NaN on AIX.

- bpo-42955: Add :data:`sys.stdlib_module_names`, containing the list of the
standard library module names. Patch by Victor Stinner.

- bpo-42944: Fix ``random.Random.sample`` when ``counts`` argument is not
``None``.

- bpo-42934: Use :class:`~traceback.TracebackException`'s new ``compact``
param in :class:`~unittest.TestResult` to reduce time and memory consumed
by traceback formatting.

- bpo-42931: Add :func:`randbytes` to ``random.__all__``.

- bpo-38250: [Enum] Flags consisting of a single bit are now considered
canonical, and will be the only flags returned from listing and iterating
over a Flag class or a Flag member. Multi-bit flags are considered
aliases; they will be returned from lookups and operations that result in
their value. Iteration for both Flag and Flag members is in definition
order.

- bpo-42877: Added the ``compact`` parameter to the constructor of
:class:`traceback.TracebackException` to reduce time and memory for use
cases that only need to call :func:`TracebackException.format` and
:func:`TracebackException.format_exception_only`.

- bpo-42923: The :c:func:`Py_FatalError` function and the
:mod:`faulthandler` module now dump the list of extension modules on a
fatal error.

- bpo-42848: Removed recursion from :class:`~traceback.TracebackException`
to allow it to handle long exception chains.

- bpo-42901: [Enum] move member creation from ``EnumMeta.__new__`` to
``_proto_member.__set_name__``, allowing members to be created and visible
in ``__init_subclass__``.

- bpo-42780: Fix os.set_inheritable() for O_PATH file descriptors on Linux.

- bpo-42866: Fix a reference leak in the ``getcodec()`` function of CJK
codecs. Patch by Victor Stinner.

- bpo-42846: Convert the 6 CJK codec extension modules (_codecs_cn,
_codecs_hk, _codecs_iso2022, _codecs_jp, _codecs_kr and _codecs_tw) to the
multiphase initialization API (:pep:`489`). Patch by Victor Stinner.

- bpo-42851: remove __init_subclass__ support for Enum members

- bpo-42834: Make internal caches of the ``_json`` module compatible with
subinterpreters.

- bpo-41748: Fix HTMLParser parsing rules for element attributes containing
commas with spaces. Patch by Karl Dubost.

- bpo-40810: Require SQLite 3.7.15 or newer. Patch by Erlend E. Aasland.

- bpo-1635741: Convert the _multibytecodec extension module (CJK codecs) to
multi-phase initialization (:pep:`489`). Patch by Erlend E. Aasland.

- bpo-42802: The distutils ``bdist_wininst`` command deprecated in Python
3.8 has been removed. The distutils ``bdist_wheel`` command is now
recommended to distribute binary packages on Windows.

- bpo-24464: The undocumented built-in function
``sqlite3.enable_shared_cache`` is now deprecated, scheduled for removal
in Python 3.12. Its use is strongly discouraged by the SQLite3
documentation. Patch by Erlend E. Aasland.

- bpo-42384: Make pdb populate sys.path[0] exactly the same as regular
python execution.

- bpo-42383: Fix pdb: previously pdb would fail to restart the debugging
target if it was specified using a relative path and the current directory
changed.

- bpo-42005: Fix CLI of :mod:`cProfile` and :mod:`profile` to catch
:exc:`BrokenPipeError`.

- bpo-41604: Don't decrement the reference count of the previous user_ptr
when set_panel_userptr fails.

- bpo-41149: Allow executing callables that have a boolean value of
``False`` when passed to :class:`Threading.thread` as the target. Patch
contributed by Barney Stratford.

- bpo-38307: Add an 'end_lineno' attribute to the Class and Function objects
that appear in the tree returned by pyclbr functions. This and the
existing 'lineno' attribute define the extent of class and def statements.
Patch by Aviral Srivastava.

- bpo-39273: The ``BUTTON5_*`` constants are now exposed in the
:mod:`curses` module if available.

- bpo-33289: Correct call to :mod:`tkinter.colorchooser` to return RGB
triplet of ints instead of floats. Patch by Cheryl Sabella.

Documentation
-------------

- bpo-40304: Fix doc for type(name, bases, dict). Patch by Boris
Verkhovskiy and Éric Araujo.

- bpo-42811: Updated importlib.utils.resolve_name() doc to use
__spec__.parent instead of __package__. (Thanks Yair Frid.)

Tests
-----

- bpo-40823: Use :meth:`unittest.TestLoader().loadTestsFromTestCase` instead
of :meth:`unittest.makeSuite` in :mod:`sqlite3` tests. Patch by Erlend E.
Aasland.

- bpo-40810: In :mod:`sqlite3`, fix ``CheckTraceCallbackContent`` for SQLite
pre 3.7.15.

Build
-----

- bpo-43031: Pass ``--timeout=$(TESTTIMEOUT)`` option to the default profile
task ``./python -m test --pgo`` command.

- bpo-36143: ``make regen-all`` now also runs ``regen-keyword``. Patch by
Victor Stinner.

- bpo-42874: Removed the grep -q and -E flags in the tzpath validation
section of the configure script to better accommodate users of some
platforms (specifically Solaris 10).

- bpo-31904: Add library search path by wr-cc in add_cross_compiling_paths()
for VxWorks.

- bpo-42856: Add ``--with-wheel-pkg-dir=PATH`` option to the ``./configure``
script. If specified, the :mod:`ensurepip` module looks for ``setuptools``
and ``pip`` wheel packages in this directory: if both are present, these
wheel packages are used instead of ensurepip bundled wheel packages.

Some Linux distribution packaging policies recommend against bundling
dependencies. For example, Fedora installs wheel packages in the
``/usr/share/python-wheels/`` directory and don't install the
``ensurepip._bundled`` package.

Windows
-------

- bpo-41837: Updated Windows installer to include OpenSSL 1.1.1i

- bpo-42584: Upgrade Windows installer to use SQLite 3.34.0.

macOS
-----

- bpo-42504: Ensure that the value of
sysconfig.get_config_var('MACOSX_DEPLOYMENT_TARGET') is always a string,
even in when the value is parsable as an integer.

IDLE
----

- bpo-43008: Make IDLE invoke :func:`sys.excepthook` in normal, 2-process
mode. Patch by Ken Hilton.

- bpo-33065: Fix problem debugging user classes with __repr__ method.

- bpo-23544: Disable Debug=>Stack Viewer when user code is running or
Debugger is active, to prevent hang or crash. Patch by Zackery Spytz.

- bpo-32631: Finish zzdummy example extension module: make menu entries
work; add docstrings and tests with 100% coverage.

C API
-----

- bpo-42979: When Python is built in debug mode (with C assertions), calling
a type slot like ``sq_length`` (``__len__()`` in Python) now fails with a
fatal error if the slot succeeded with an exception set, or failed with no
exception set. The error message contains the slot, the type name, and the
current exception (if an exception is set). Patch by Victor Stinner.

- bpo-43030: Fixed a compiler warning in :c:func:`Py_UNICODE_ISSPACE()` on
platforms with signed ``wchar_t``.

What's New in Python 3.10.0 alpha 4?
====================================

*Release date: 2021-01-04*

Core and Builtins
-----------------

- bpo-42814: Fix undefined behavior in ``Objects/genericaliasobject.c``.

- bpo-42806: Fix the column offsets for f-strings :mod:`ast` nodes
surrounded by parentheses and for nodes that spawn multiple lines. Patch
by Pablo Galindo.

- bpo-40631: Fix regression where a single parenthesized starred expression
was a valid assignment target.

- bpo-27794: Improve the error message for failed writes/deletes to property
objects. When possible, the attribute name is now shown. Patch provided by
Yurii Karabas.

- bpo-42745: Make the type attribute lookup cache per-interpreter. Patch by
Victor Stinner.

- bpo-42246: Jumps to jumps are not eliminated when it would break PEP 626.

- bpo-42246: Make sure that the ``f_lasti`` and ``f_lineno`` attributes of a
frame are set correctly when an exception is raised or re-raised. Required
for PEP 626.

- bpo-32381: The coding cookie (ex: ``# coding: latin1``) is now ignored in
the command passed to the :option:`-c` command line option. Patch by
Victor Stinner.

- bpo-30858: Improve error location in expressions that contain assignments.
Patch by Pablo Galindo and Lysandros Nikolaou.

- bpo-42615: Remove jump commands made redundant by the deletion of
unreachable bytecode blocks

- bpo-42639: Make the :mod:`atexit` module state per-interpreter. It is now
safe have more than one :mod:`atexit` module instance. Patch by Dong-hee
Na and Victor Stinner.

- bpo-32381: Fix encoding name when running a ``.pyc`` file on Windows:
:c:func:`PyRun_SimpleFileExFlags()` now uses the correct encoding to
decode the filename.

- bpo-42195: The ``__args__`` of the parameterized generics for
:data:`typing.Callable` and :class:`collections.abc.Callable` are now
consistent. The ``__args__`` for :class:`collections.abc.Callable` are
now flattened while :data:`typing.Callable`'s have not changed. To allow
this change, :class:`types.GenericAlias` can now be subclassed and
``collections.abc.Callable``'s ``__class_getitem__`` will now return a
subclass of ``types.GenericAlias``. Tests for typing were also updated to
not subclass things like ``Callable[..., T]`` as that is not a valid base
class. Finally, both ``Callable``\ s no longer validate their
``argtypes``, in ``Callable[[argtypes], resulttype]`` to prepare for
:pep:`612`. Patch by Ken Jin.

- bpo-40137: Convert functools module to use
:c:func:`PyType_FromModuleAndSpec`.

- bpo-40077: Convert :mod:`array` to use heap types, and establish module
state for these.

- bpo-42008: Fix _random.Random() seeding.

- bpo-1635741: Port the :mod:`pyexpat` extension module to multi-phase
initialization (:pep:`489`).

- bpo-40521: Make the Unicode dictionary of interned strings compatible with
subinterpreters. Patch by Victor Stinner.

- bpo-39465: Make :c:func:`_PyUnicode_FromId` function compatible with
subinterpreters. Each interpreter now has an array of identifier objects
(interned strings decoded from UTF-8). Patch by Victor Stinner.

Library
-------

- bpo-42257: Handle empty string in variable executable in
platform.libc_ver()

- bpo-42772: randrange() now raises a TypeError when step is specified
without a stop argument. Formerly, it silently ignored the step argument.

- bpo-42759: Fixed equality comparison of :class:`tkinter.Variable` and
:class:`tkinter.font.Font`. Objects which belong to different Tcl
interpreters are now always different, even if they have the same name.

- bpo-42756: Configure LMTP Unix-domain socket to use socket global default
timeout when a timeout is not explicitly provided.

- bpo-23328: Allow / character in username, password fields on _PROXY
envars.

- bpo-42740: :func:`typing.get_args` and :func:`typing.get_origin` now
support :pep:`604` union types and :pep:`612` additions to ``Callable``.

- bpo-42655: :mod:`subprocess` *extra_groups* is now correctly passed into
setgroups() system call.

- bpo-42727: ``EnumMeta.__prepare__`` now accepts ``**kwds`` to properly
support ``__init_subclass__``

- bpo-38308: Add optional *weights* to *statistics.harmonic_mean()*.

- bpo-42721: When simple query dialogs (:mod:`tkinter.simpledialog`),
message boxes (:mod:`tkinter.messagebox`) or color choose dialog
(:mod:`tkinter.colorchooser`) are created without arguments *master* and
*parent*, and the default root window is not yet created, and
:func:`~tkinter.NoDefaultRoot` was not called, a new temporal hidden root
window will be created automatically. It will not be set as the default
root window and will be destroyed right after closing the dialog window.
It will help to use these simple dialog windows in programs which do not
need other GUI.

- bpo-25246: Optimized :meth:`collections.deque.remove`.

- bpo-35728: Added a root parameter to :func:`tkinter.font.nametofont`.

- bpo-15303: :mod:`tkinter` supports now widgets with boolean value False.

- bpo-42681: Fixed range checks for color and pair numbers in :mod:`curses`.

- bpo-42685: Improved placing of simple query windows in Tkinter (such as
:func:`tkinter.simpledialog.askinteger`). They are now centered at the
center of the parent window if it is specified and shown, otherwise at the
center of the screen.

- bpo-9694: Argparse help no longer uses the confusing phrase, "optional
arguments". It uses "options" instead.

- bpo-1635741: Port the :mod:`_thread` extension module to the multiphase
initialization API (:pep:`489`) and convert its static types to heap
types.

- bpo-37961: Fix crash in :func:`tracemalloc.Traceback.__repr__` (regressed
in Python 3.9).

- bpo-42630: :mod:`tkinter` functions and constructors which need a default
root window raise now :exc:`RuntimeError` with descriptive message instead
of obscure :exc:`AttributeError` or :exc:`NameError` if it is not created
yet or cannot be created automatically.

- bpo-42639: :func:`atexit._run_exitfuncs` now logs callback exceptions
using :data:`sys.unraisablehook`, rather than logging them directly into
:data:`sys.stderr` and raise the last exception.

- bpo-42644: ``logging.disable`` will now validate the types and value of
its parameter. It also now accepts strings representing the levels (as
does ``loging.setLevel``) instead of only the numerical values.

- bpo-42639: At Python exit, if a callback registered with
:func:`atexit.register` fails, its exception is now logged. Previously,
only some exceptions were logged, and the last exception was always
silently ignored.

- bpo-36541: Fixed lib2to3.pgen2 to be able to parse PEP-570 positional only
argument syntax.

- bpo-42382: In ``importlib.metadata``: - ``EntryPoint`` objects now expose
a ``.dist`` object referencing the ``Distribution`` when constructed from
a ``Distribution``. - Add support for package discovery under package
normalization rules. - The object returned by ``metadata()`` now has a
formally defined protocol called ``PackageMetadata`` with declared support
for the ``.get_all()`` method. - Synced with importlib_metadata 3.3.

- bpo-41877: A check is added against misspellings of autospect, auto_spec
and set_spec being passed as arguments to patch, patch.object and
create_autospec.

- bpo-39717: [tarfile] update nested exception raising to use ``from None``
or ``from e``

- bpo-41877: AttributeError for suspected misspellings of assertions on
mocks are now pointing out that the cause are misspelled assertions and
also what to do if the misspelling is actually an intended attribute name.
The unittest.mock document is also updated to reflect the current set of
recognised misspellings.

- bpo-41559: Implemented :pep:`612`: added ``ParamSpec`` and ``Concatenate``
to :mod:`typing`. Patch by Ken Jin.

- bpo-42385: StrEnum: fix _generate_next_value_ to return a str

- bpo-31904: Define THREAD_STACK_SIZE for VxWorks.

- bpo-34750: [Enum] `_EnumDict.update()` is now supported

- bpo-42517: Enum: private names do not become members / do not generate
errors -- they remain normal attributes

- bpo-42678: ``Enum``: call ``__init_subclass__`` after members have been
added

- bpo-28964: :func:`ast.literal_eval` adds line number information (if
available) in error message for malformed nodes.

- bpo-42470: :func:`random.sample` no longer warns on a sequence which is
also a set.

- bpo-31904: :func:`posixpath.expanduser` returns the input *path* unchanged
if user home directory is None on VxWorks.

- bpo-42388: Fix subprocess.check_output(..., input=None) behavior when
text=True to be consistent with that of the documentation and
universal_newlines=True.

- bpo-34463: Fixed discrepancy between :mod:`traceback` and the interpreter
in formatting of SyntaxError with lineno not set (:mod:`traceback` was
changed to match interpreter).

- bpo-42393: Raise :exc:`OverflowError` instead of silent truncation in
:meth:`socket.ntohs` and :meth:`socket.htons`. Silent truncation was
deprecated in Python 3.7. Patch by Erlend E. Aasland

- bpo-42222: Harmonized :func:`random.randrange` argument handling to match
:func:`range`.

* The integer test and conversion in ``randrange()`` now uses
:func:`operator.index`.
* Non-integer arguments to ``randrange()`` are deprecated.
* The ``ValueError`` is deprecated in favor of a ``TypeError``.
* It now runs a little faster than before.

(Contributed by Raymond Hettinger and Serhiy Storchaka.)

- bpo-42163: Restore compatibility for ``uname_result`` around deepcopy and
_replace.

- bpo-42090: ``zipfile.Path.joinpath`` now accepts arbitrary arguments, same
as ``pathlib.Path.joinpath``.

- bpo-1635741: Port the _csv module to the multi-phase initialization API
(:pep:`489`).

- bpo-42059: :class:`typing.TypedDict` types created using the alternative
call-style syntax now correctly respect the ``total`` keyword argument
when setting their ``__required_keys__`` and ``__optional_keys__`` class
attributes.

- bpo-41960: Add ``globalns`` and ``localns`` parameters to the
:func:`inspect.signature` and :meth:`inspect.Signature.from_callable`.

- bpo-41907: fix ``format()`` behavior for ``IntFlag``

- bpo-41891: Ensure asyncio.wait_for waits for task completion

- bpo-24792: Fixed bug where :mod:`zipimporter` sometimes reports an
incorrect cause of import errors.

- bpo-31904: Fix site and sysconfig modules for VxWorks RTOS which has no
home directories.

- bpo-41462: Add :func:`os.set_blocking()` support for VxWorks RTOS.

- bpo-40219: Lowered :class:`tkinter.ttk.LabeledScale` dummy widget to
prevent hiding part of the content label.

- bpo-37193: Fixed memory leak in ``socketserver.ThreadingMixIn`` introduced
in Python 3.7.

- bpo-39068: Fix initialization race condition in :func:`a85encode` and
:func:`b85encode` in :mod:`base64`. Patch by Brandon Stansbury.

Documentation
-------------

- bpo-17140: Add documentation for the
:class:`multiprocessing.pool.ThreadPool` class.

- bpo-34398: Prominently feature listings from the glossary in documentation
search results. Patch by Ammar Askar.

Tests
-----

- bpo-42794: Update test_nntplib to use official group name of news.aioe.org
for testing. Patch by Dong-hee Na.

- bpo-31904: Skip some asyncio tests on VxWorks.

- bpo-42641: Enhance ``test_select.test_select()``: it now takes 500
milliseconds rather than 10 seconds. Use Python rather than a shell to
make the test more portable.

- bpo-31904: Skip some tests in _test_all_chown_common() on VxWorks.

- bpo-42199: Fix bytecode helper assertNotInBytecode.

- bpo-41443: Add more attribute checking in test_posix.py

- bpo-31904: Disable os.popen and impacted tests on VxWorks

- bpo-41439: Port test_ssl and test_uuid to VxWorks RTOS.

Build
-----

- bpo-42692: Fix __builtin_available check on older compilers. Patch by
Joshua Root.

- bpo-27640: Added ``--disable-test-modules`` option to the ``configure``
script: don't build nor install test modules. Patch by Xavier de Gaye,
Thomas Petazzoni and Peixing Xin.

- bpo-42604: Now all platforms use a value for the "EXT_SUFFIX" build
variable derived from SOABI (for instance in freeBSD, "EXT_SUFFIX" is now
".cpython-310d.so" instead of ".so"). Previously only Linux, Mac and
VxWorks were using a value for "EXT_SUFFIX" that included "SOABI".

- bpo-42598: Fix implicit function declarations in configure which could
have resulted in incorrect configuration checks. Patch contributed by
Joshua Root.

- bpo-31904: Enable libpython3.so for VxWorks.

- bpo-29076: Add fish shell support to macOS installer.

macOS
-----

- bpo-42361: Update macOS installer build to use Tcl/Tk 8.6.11 (rc2,
expected to be final release).

- bpo-41837: Update macOS installer build to use OpenSSL 1.1.1i.

- bpo-42584: Update macOS installer to use SQLite 3.34.0.

Tools/Demos
-----------

- bpo-42726: Fixed Python 3 compatibility issue with gdb/libpython.py
handling of attribute dictionaries.

- bpo-42613: Fix ``freeze.py`` tool to use the prope config and library
directories. Patch by Victor Stinner.

C API
-----

- bpo-42591: Export the :c:func:`Py_FrozenMain` function: fix a Python 3.9.0
regression. Python 3.9 uses ``-fvisibility=hidden`` and the function was
not exported explicitly and so not exported.

- bpo-32381: Remove the private :c:func:`_Py_fopen` function which is no
longer needed. Use :c:func:`_Py_wfopen` or :c:func:`_Py_fopen_obj`
instead. Patch by Victor Stinner.

- bpo-1635741: Port :mod:`resource` extension module to module state

- bpo-42111: Update the ``xxlimited`` module to be a better example of how
to use the limited C API.

- bpo-40052: Fix an alignment build warning/error in function
``PyVectorcall_Function()``. Patch by Andreas Schneider, Antoine Pitrou
and Petr Viktorin.

What's New in Python 3.10.0 alpha 3?
====================================

*Release date: 2020-12-07*

Security
--------

- bpo-40791: Add ``volatile`` to the accumulator variable in
``hmac.compare_digest``, making constant-time-defeating optimizations less
likely.

Core and Builtins
-----------------

- bpo-42576: ``types.GenericAlias`` will now raise a ``TypeError`` when
attempting to initialize with a keyword argument. Previously, this would
cause the interpreter to crash if the interpreter was compiled with debug
symbols. This does not affect interpreters compiled for release. Patch by
Ken Jin.

- bpo-42536: Several built-in and standard library types now ensure that
their internal result tuples are always tracked by the :term:`garbage
collector <garbage collection>`:

- :meth:`collections.OrderedDict.items() <collections.OrderedDict>`

- :meth:`dict.items`

- :func:`enumerate`

- :func:`functools.reduce`

- :func:`itertools.combinations`

- :func:`itertools.combinations_with_replacement`

- :func:`itertools.permutations`

- :func:`itertools.product`

- :func:`itertools.zip_longest`

- :func:`zip`

Previously, they could have become untracked by a prior garbage
collection. Patch by Brandt Bucher.

- bpo-42500: Improve handling of exceptions near recursion limit. Converts a
number of Fatal Errors in RecursionErrors.

- bpo-42246: PEP 626: After a return, the f_lineno attribute of a frame is
always the last line executed.

- bpo-42435: Speed up comparison of bytes objects with non-bytes objects
when option :option:`-b` is specified. Speed up comparison of bytarray
objects with non-buffer object.

- bpo-1635741: Port the ``_warnings`` extension module to the multi-phase
initialization API (:pep:`489`). Patch by Victor Stinner.

- bpo-41686: On Windows, the ``SIGINT`` event, ``_PyOS_SigintEvent()``, is
now created even if Python is configured to not install signal handlers
(if :c:member:`PyConfig.install_signal_handlers` equals to 0, or
``Py_InitializeEx(0)``).

- bpo-42381: Allow assignment expressions in set literals and set
comprehensions as per PEP 572. Patch by Pablo Galindo.

- bpo-42202: Change function parameters annotations internal representation
to tuple of strings. Patch provided by Yurii Karabas.

- bpo-42374: Fix a regression introduced by the new parser, where an
unparenthesized walrus operator was not allowed within generator
expressions.

- bpo-42316: Allow an unparenthesized walrus in subscript indexes.

- bpo-42349: Make sure that the compiler front-end produces a well-formed
control flow graph. Be be more aggressive in the compiler back-end, as it
is now safe to do so.

- bpo-42296: On Windows, fix a regression in signal handling which prevented
to interrupt a program using CTRL+C. The signal handler can be run in a
thread different than the Python thread, in which case the test deciding
if the thread can handle signals is wrong.

- bpo-42332: :class:`types.GenericAlias` objects can now be the targets of
weakrefs.

- bpo-42282: Optimise constant subexpressions that appear as part of named
expressions (previously the AST optimiser did not descend into named
expressions). Patch by Nick Coghlan.

- bpo-42266: Fixed a bug with the LOAD_ATTR opcode cache that was not
respecting monkey-patching a class-level attribute to make it a
descriptor. Patch by Pablo Galindo.

- bpo-40077: Convert :mod:`queue` to use heap types.

- bpo-42246: Improved accuracy of line tracing events and f_lineno attribute
of Frame objects. See PEP 626 for details.

- bpo-40077: Convert :mod:`mmap` to use heap types.

- bpo-42233: Allow ``GenericAlias`` objects to use :ref:`union type
expressions <types-union>`. This allows expressions like ``list[int] |
dict[float, str]`` where previously a ``TypeError`` would have been
thrown. This also fixes union type expressions not de-duplicating
``GenericAlias`` objects. (Contributed by Ken Jin in :issue:`42233`.)

- bpo-26131: The import system triggers a `ImportWarning` when it falls back
to using `load_module()`.

Library
-------

- bpo-5054: CGIHTTPRequestHandler.run_cgi() HTTP_ACCEPT improperly parsed.
Replace the special purpose getallmatchingheaders with generic get_all
method and add relevant tests.

Original Patch by Martin Panter. Modified by Senthil Kumaran.

- bpo-42562: Fix issue when dis failed to parse function that has no line
numbers. Patch provided by Yurii Karabas.

- bpo-17735: :func:`inspect.findsource` now raises :exc:`OSError` instead of
:exc:`IndexError` when :attr:`co_lineno` of a code object is greater than
the file length. This can happen, for example, when a file is edited after
it was imported. PR by Irit Katriel.

- bpo-42116: Fix handling of trailing comments by :func:`inspect.getsource`.

- bpo-42532: Remove unexpected call of ``__bool__`` when passing a
``spec_arg`` argument to a Mock.

- bpo-38200: Added itertools.pairwise()

- bpo-41818: Fix test_master_read() so that it succeeds on all platforms
that either raise OSError or return b"" upon reading from master.

- bpo-42487: ChainMap.__iter__ no longer calls __getitem__ on underlying
maps

- bpo-42482: :class:`~traceback.TracebackException` no longer holds a
reference to the exception's traceback object. Consequently, instances of
TracebackException for equivalent but non-equal exceptions now compare as
equal.

- bpo-41818: Make test_openpty() avoid unexpected success due to number of
rows and/or number of columns being == 0.

- bpo-42392: Remove loop parameter from ``asyncio.subprocess`` and
``asyncio.tasks`` functions. Patch provided by Yurii Karabas.

- bpo-42392: Remove loop parameter from ``asyncio.open_connection`` and
``asyncio.start_server`` functions. Patch provided by Yurii Karabas.

- bpo-28468: Add :func:`platform.freedesktop_os_release` function to parse
freedesktop.org ``os-release`` files.

- bpo-42299: Removed the ``formatter`` module, which was deprecated in
Python 3.4. It is somewhat obsolete, little used, and not tested. It was
originally scheduled to be removed in Python 3.6, but such removals were
delayed until after Python 2.7 EOL. Existing users should copy whatever
classes they use into their code. Patch by Dong-hee Na and and Terry J.
Reedy.

- bpo-26131: Deprecate zipimport.zipimporter.load_module() in favour of
exec_module().

- bpo-41818: Updated tests for the pty library. test_basic() has been
changed to test_openpty(); this additionally checks if slave termios and
slave winsize are being set properly by pty.openpty(). In order to add
support for FreeBSD, NetBSD, OpenBSD, and Darwin, this also adds
test_master_read(), which demonstrates that pty.spawn() should not depend
on an OSError to exit from its copy loop.

- bpo-42392: Remove loop parameter from ``__init__`` in all
``asyncio.locks`` and ``asyncio.Queue`` classes. Patch provided by Yurii
Karabas.

- bpo-15450: Make :class:`filecmp.dircmp` respect subclassing. Now the
:attr:`filecmp.dircmp.subdirs` behaves as expected when subclassing
dircmp.

- bpo-42413: The exception :exc:`socket.timeout` is now an alias of
:exc:`TimeoutError`.

- bpo-31904: Support signal module on VxWorks.

- bpo-42406: We fixed an issue in `pickle.whichmodule` in which importing
`multiprocessing` could change the how pickle identifies which module an
object belongs to, potentially breaking the unpickling of those objects.

- bpo-42403: Simplify the :mod:`importlib` external bootstrap code:
``importlib._bootstrap_external`` now uses regular imports to import
builtin modules. When it is imported, the builtin :func:`__import__()`
function is already fully working and so can be used to import builtin
modules like :mod:`sys`. Patch by Victor Stinner.

- bpo-1635741: Convert _sre module types to heap types (PEP 384). Patch by
Erlend E. Aasland.

- bpo-42375: subprocess module update for DragonFlyBSD support.

- bpo-41713: Port the ``_signal`` extension module to the multi-phase
initialization API (:pep:`489`). Patch by Victor Stinner and Mohamed
Koubaa.

- bpo-37205: :func:`time.time()`, :func:`time.perf_counter()` and
:func:`time.monotonic()` functions can no longer fail with a Python fatal
error, instead raise a regular Python exception on failure.

- bpo-42328: Fixed :meth:`tkinter.ttk.Style.map`. The function accepts now
the representation of the default state as empty sequence (as returned by
``Style.map()``). The structure of the result is now the same on all
platform and does not depend on the value of ``wantobjects``.

- bpo-42345: Fix various issues with ``typing.Literal`` parameter handling
(flatten, deduplicate, use type to cache key). Patch provided by Yurii
Karabas.

- bpo-37205: :func:`time.perf_counter()` on Windows and
:func:`time.monotonic()` on macOS are now system-wide. Previously, they
used an offset computed at startup to reduce the precision loss caused by
the float type. Use :func:`time.perf_counter_ns()` and
:func:`time.monotonic_ns()` added in Python 3.7 to avoid this precision
loss.

- bpo-42318: Fixed support of non-BMP characters in :mod:`tkinter` on macOS.

- bpo-42350: Fix the :class:`threading.Thread` class at fork: do nothing if
the thread is already stopped (ex: fork called at Python exit).
Previously, an error was logged in the child process.

- bpo-42333: Port _ssl extension module to heap types.

- bpo-42014: The ``onerror`` callback from ``shutil.rmtree`` now receives
correct function when ``os.open`` fails.

- bpo-42237: Fix `os.sendfile()` on illumos.

- bpo-42308: Add :data:`threading.__excepthook__` to allow retrieving the
original value of :func:`threading.excepthook` in case it is set to a
broken or a different value. Patch by Mario Corchero.

- bpo-42131: Implement PEP 451/spec methods on zipimport.zipimporter:
find_spec(), create_module(), and exec_module().

This also allows for the documented deprecation of find_loader(),
find_module(), and load_module().

- bpo-41877: Mock objects which are not unsafe will now raise an
AttributeError if an attribute with the prefix asert, aseert, or assrt is
accessed, in addition to this already happening for the prefixes assert or
assret.

- bpo-42264: ``sqlite3.OptimizedUnicode`` has been undocumented and obsolete
since Python 3.3, when it was made an alias to :class:`str`. It is now
deprecated, scheduled for removal in Python 3.12.

- bpo-42251: Added :func:`threading.gettrace` and
:func:`threading.getprofile` to retrieve the functions set by
:func:`threading.settrace` and :func:`threading.setprofile` respectively.
Patch by Mario Corchero.

- bpo-42249: Fixed writing binary Plist files larger than 4 GiB.

- bpo-42236: On Unix, the :func:`os.device_encoding` function now returns
``'UTF-8'`` rather than the device encoding if the :ref:`Python UTF-8 Mode
<utf8-mode>` is enabled.

- bpo-41754: webbrowser: Ignore *NotADirectoryError* when calling
``xdg-settings``.

- bpo-42183: Fix a stack overflow error for asyncio Task or Future repr().

The overflow occurs under some circumstances when a Task or Future
recursively returns itself.

- bpo-42140: Improve asyncio.wait function to create the futures set just
one time.

- bpo-42133: Update various modules in the stdlib to fall back on
`__spec__.loader` when `__loader__` isn't defined on a module.

- bpo-26131: The `load_module()` methods found in importlib now trigger a
DeprecationWarning.

- bpo-39825: Windows: Change ``sysconfig.get_config_var('EXT_SUFFIX')`` to
the expected full ``platform_tag.extension`` format. Previously it was
hard-coded to ``.pyd``, now it is compatible with ``distutils.sysconfig``
and will result in something like ``.cp38-win_amd64.pyd``. This brings
windows into conformance with the other platforms.

- bpo-26389: The :func:`traceback.format_exception`,
:func:`traceback.format_exception_only`, and
:func:`traceback.print_exception` functions can now take an exception
object as a positional-only argument.

- bpo-41889: Enum: fix regression involving inheriting a multiply inherited
enum

- bpo-41861: Convert :mod:`sqlite3` to use heap types (PEP 384). Patch by
Erlend E. Aasland.

- bpo-40624: Added support for the XPath ``!=`` operator in xml.etree

- bpo-28850: Fix :meth:`pprint.PrettyPrinter.format` overrides being ignored
for contents of small containers. The :func:`pprint._safe_repr` function
was removed.

- bpo-41625: Expose the :c:func:`splice` as :func:`os.splice` in the
:mod:`os` module. Patch by Pablo Galindo

- bpo-34215: Clarify the error message for
:exc:`asyncio.IncompleteReadError` when ``expected`` is ``None``.

- bpo-41543: Add async context manager support for contextlib.nullcontext.

- bpo-21041: :attr:`pathlib.PurePath.parents` now supports negative
indexing. Patch contributed by Yaroslav Pankovych.

- bpo-41332: Added missing connect_accepted_socket() method to
``asyncio.AbstractEventLoop``.

- bpo-12800: Extracting a symlink from a tarball should succeed and
overwrite the symlink if it already exists. The fix is to remove the
existing file or symlink before extraction. Based on patch by Chris AtLee,
Jeffrey Kintscher, and Senthil Kumaran.

- bpo-40968: :mod:`urllib.request` and :mod:`http.client` now send
``http/1.1`` ALPN extension during TLS handshake when no custom context is
supplied.

- bpo-41001: Add func:`os.eventfd` to provide a low level interface for
Linux's event notification file descriptor.

- bpo-40816: Add AsyncContextDecorator to contextlib to support async
context manager as a decorator.

- bpo-40550: Fix time-of-check/time-of-action issue in
subprocess.Popen.send_signal.

- bpo-39411: Add an ``is_async`` identifier to :mod:`pyclbr`'s ``Function``
objects. Patch by Batuhan Taskaya

- bpo-35498: Add slice support to :attr:`pathlib.PurePath.parents`.

Documentation
-------------

- bpo-42238: Tentative to deprecate ``make suspicious`` by first removing it
from the CI and documentation builds, but keeping it around for manual
uses.

- bpo-42153: Fix the URL for the IMAP protocol documents.

- bpo-41028: Language and version switchers, previously maintained in every
cpython branches, are now handled by docsbuild-script.

Tests
-----

- bpo-41473: Re-enable test_gdb on gdb 9.2 and newer:
https://bugzilla.redhat.com/show_bug.cgi?id=1866884 bug is fixed in gdb
10.1.

- bpo-42553: Fix ``test_asyncio.test_call_later()`` race condition: don't
measure asyncio performance in the ``call_later()`` unit test. The test
failed randomly on the CI.

- bpo-31904: Fix test_netrc on VxWorks: create temporary directories using
temp_cwd().

- bpo-31904: skip test_getaddrinfo_ipv6_scopeid_symbolic and
test_getnameinfo_ipv6_scopeid_symbolic on VxWorks

- bpo-31904: skip test_test of test_mailcap on VxWorks

- bpo-31904: add shell requirement for test_pipes

- bpo-31904: skip some tests related to fifo on VxWorks

- bpo-31904: Fix test_doctest.py failures for VxWorks.

- bpo-40754: Include ``_testinternalcapi`` module in Windows installer for
test suite

- bpo-41561: test_ssl: skip test_min_max_version_mismatch when TLS 1.0 is
not available

- bpo-31904: Fix os module failures for VxWorks RTOS.

- bpo-31904: Fix fifo test cases for VxWorks RTOS.

Build
-----

- bpo-31904: remove libnet dependency from detect_socket() for VxWorks

- bpo-42398: Fix a race condition in "make regen-all" when make -jN option
is used to run jobs in parallel. The clinic.py script now only use atomic
write to write files. Moveover, generated files are now left unchanged if
the content does not change, to not change the file modification time.

- bpo-41617: Fix building ``pycore_bitutils.h`` internal header on old clang
version without ``__builtin_bswap16()`` (ex: Xcode 4.6.3 on Mac OS X
10.7). Patch by Joshua Root and Victor Stinner.

- bpo-38823: It is no longer possible to build the ``_ctypes`` extension
module without :c:type:`wchar_t` type: remove ``CTYPES_UNICODE`` macro.
Anyway, the :c:type:`wchar_t` type is required to build Python. Patch by
Victor Stinner.

- bpo-42087: Support was removed for AIX 5.3 and below. See :issue:`40680`.

- bpo-40998: Addressed three compiler warnings found by undefined behavior
sanitizer (ubsan).

Windows
-------

- bpo-42120: Remove macro definition of ``copysign`` (to ``_copysign``) in
headers.

- bpo-38506: The Windows launcher now properly handles Python 3.10 when
listing installed Python versions.

macOS
-----

- bpo-42504: Fix build on macOS Big Sur when MACOSX_DEPLOYMENT_TARGET=11

- bpo-41116: Ensure distutils.unixxcompiler.find_library_file can find
system provided libraries on macOS 11.

- bpo-41100: Add support for macOS 11 and Apple Silicon systems.

It is now possible to build "Universal 2" binaries using
"--enable-universalsdk --with-universal-archs=universal2".

Binaries build on later macOS versions can be deployed back to older
versions (tested up to macOS 10.9), when using the correct deployment
target. This is tested using Xcode 11 and later.

- bpo-42232: Added Darwin specific madvise options to mmap module.

- bpo-38443: The ``--enable-universalsdk`` and ``--with-universal-archs``
options for the configure script now check that the specified
architectures can be used.

IDLE
----

- bpo-42508: Keep IDLE running on macOS. Remove obsolete workaround that
prevented running files with shortcuts when using new universal2
installers built on macOS 11.

- bpo-42426: Fix reporting offset of the RE error in searchengine.

- bpo-42415: Get docstrings for IDLE calltips more often by using
inspect.getdoc.

Tools/Demos
-----------

- bpo-42212: The smelly.py script now also checks the Python dynamic library
and extension modules, not only the Python static library. Make also the
script more verbose: explain what it does.

- bpo-36310: Allow :file:`Tools/i18n/pygettext.py` to detect calls to
``gettext`` in f-strings.

C API
-----

- bpo-42423: The :c:func:`PyType_FromSpecWithBases` and
:c:func:`PyType_FromModuleAndSpec` functions now accept a single class as
the *bases* argument.

- bpo-1635741: Port :mod:`select` extension module to multiphase
initialization (:pep:`489`).

- bpo-1635741: Port _posixsubprocess extension module to multiphase
initialization (:pep:`489`).

- bpo-1635741: Port _posixshmem extension module to multiphase
initialization (:pep:`489`)

- bpo-1635741: Port _struct extension module to multiphase initialization
(:pep:`489`)

- bpo-1635741: Port :mod:`spwd` extension module to multiphase
initialization (:pep:`489`)

- bpo-1635741: Port :mod:`gc` extension module to multiphase initialization
(:pep:`489`)

- bpo-1635741: Port _queue extension module to multiphase initialization
(:pep:`489`)

- bpo-39573: Convert :c:func:`Py_TYPE` and :c:func:`Py_SIZE` back to macros
to allow using them as an l-value. Many third party C extension modules
rely on the ability of using Py_TYPE() and Py_SIZE() to set an object type
and size: ``Py_TYPE(obj) = type;`` and ``Py_SIZE(obj) = size;``.

- bpo-1635741: Port :mod:`symtable` extension module to multiphase
initialization (:pep:`489`)

- bpo-1635741: Port :mod:`grp` and :mod:`pwd` extension modules to
multiphase initialization (:pep:`489`)

- bpo-1635741: Port _random extension module to multiphase initialization
(:pep:`489`)

- bpo-1635741: Port _hashlib extension module to multiphase initialization
(:pep:`489`)

- bpo-41713: Removed the undocumented ``PyOS_InitInterrupts()`` function.
Initializing Python already implicitly installs signal handlers: see
:c:member:`PyConfig.install_signal_handlers`. Patch by Victor Stinner.

- bpo-40170: The ``Py_TRASHCAN_BEGIN`` macro no longer accesses PyTypeObject
attributes, but now can get the condition by calling the new private
:c:func:`_PyTrash_cond()` function which hides implementation details.

- bpo-42260: :c:func:`Py_GetPath`, :c:func:`Py_GetPrefix`,
:c:func:`Py_GetExecPrefix`, :c:func:`Py_GetProgramFullPath`,
:c:func:`Py_GetPythonHome` and :c:func:`Py_GetProgramName` functions now
return ``NULL`` if called before :c:func:`Py_Initialize` (before Python is
initialized). Use the new :ref:`Python Initialization Configuration API
<init-config>` to get the :ref:`Python Path Configuration.
<init-path-config>`. Patch by Victor Stinner.

- bpo-42260: The :c:func:`PyConfig_Read` function now only parses
:c:member:`PyConfig.argv` arguments once: :c:member:`PyConfig.parse_argv`
is set to ``2`` after arguments are parsed. Since Python arguments are
strippped from :c:member:`PyConfig.argv`, parsing arguments twice would
parse the application options as Python options.

- bpo-42262: Added :c:func:`Py_NewRef` and :c:func:`Py_XNewRef` functions to
increment the reference count of an object and return the object. Patch by
Victor Stinner.

- bpo-42260: When :c:func:`Py_Initialize` is called twice, the second call
now updates more :mod:`sys` attributes for the configuration, rather than
only :data:`sys.argv`. Patch by Victor Stinner.

- bpo-41832: The :c:func:`PyType_FromModuleAndSpec` function now accepts
NULL ``tp_doc`` slot.

- bpo-1635741: Added :c:func:`PyModule_AddObjectRef` function: similar to
:c:func:`PyModule_AddObject` but don't steal a reference to the value on
success. Patch by Victor Stinner.

- bpo-42171: The :c:data:`METH_FASTCALL` calling convention is added to the
limited API. The functions :c:func:`PyModule_AddType`,
:c:func:`PyType_FromModuleAndSpec`, :c:func:`PyType_GetModule` and
:c:func:`PyType_GetModuleState` are added to the limited API on Windows.

- bpo-42085: Add dedicated entry to PyAsyncMethods for sending values

- bpo-41073: :c:func:`PyType_GetSlot()` can now accept static types.

- bpo-30459: :c:func:`PyList_SET_ITEM`, :c:func:`PyTuple_SET_ITEM` and
:c:func:`PyCell_SET` macros can no longer be used as l-value or r-value.
For example, ``x = PyList_SET_ITEM(a, b, c)`` and ``PyList_SET_ITEM(a, b,
c) = x`` now fail with a compiler error. It prevents bugs like ``if
(PyList_SET_ITEM (a, b, c) < 0) ...`` test. Patch by Zackery Spytz and
Victor Stinner.

What's New in Python 3.10.0 alpha 2?
====================================

*Release date: 2020-11-03*

Security
--------

- bpo-42103: Prevented potential DoS attack via CPU and RAM exhaustion when
processing malformed Apple Property List files in binary format.

- bpo-42051: The :mod:`plistlib` module no longer accepts entity
declarations in XML plist files to avoid XML vulnerabilities. This should
not affect users as entity declarations are not used in regular plist
files.

Core and Builtins
-----------------

- bpo-42236: If the ``nl_langinfo(CODESET)`` function returns an empty
string, Python now uses UTF-8 as the filesystem encoding. Patch by Victor
Stinner.

- bpo-42218: Fixed a bug in the PEG parser that was causing crashes in debug
mode. Now errors are checked in left-recursive rules to avoid cases where
such errors do not get handled in time and appear as long-distance crashes
in other places.

- bpo-42214: Fixed a possible crash in the PEG parser when checking for the
'!=' token in the ``barry_as_flufl`` rule. Patch by Pablo Galindo.

- bpo-42206: Propagate and raise the errors caused by
:c:func:`PyAST_Validate` in the parser.

- bpo-41796: The :mod:`ast` module internal state is now per interpreter.
Patch by Victor Stinner.

- bpo-42143: Fix handling of errors during creation of ``PyFunctionObject``,
which resulted in operations on uninitialized memory. Patch by Yonatan
Goldschmidt.

- bpo-41659: Fix a bug in the parser, where a curly brace following a
`primary` didn't fail immediately. This led to invalid expressions like `a
{b}` to throw a :exc:`SyntaxError` with a wrong offset, or invalid
expressions ending with a curly brace like `a {` to not fail immediately
in the REPL.

- bpo-42150: Fix possible buffer overflow in the new parser when checking
for continuation lines. Patch by Pablo Galindo.

- bpo-42123: Run the parser two times. On the first run, disable all the
rules that only generate better error messages to gain performance. If
there's a parse failure, run the parser a second time with those enabled.

- bpo-42093: The ``LOAD_ATTR`` instruction now uses new "per opcode cache"
mechanism and it is about 36% faster now. Patch by Pablo Galindo and Yury
Selivanov.

- bpo-42030: Support for the legacy AIX-specific shared library loading
support has been removed. All versions of AIX since 4.3 have supported and
defaulted to using the common Unix mechanism instead.

- bpo-41984: The garbage collector now tracks all user-defined classes.
Patch by Brandt Bucher.

- bpo-41993: Fixed potential issues with removing not completely initialized
module from ``sys.modules`` when import fails.

- bpo-41979: Star-unpacking is now allowed for with item's targets in the
PEG parser.

- bpo-41974: Removed special methods ``__int__``, ``__float__``,
``__floordiv__``, ``__mod__``, ``__divmod__``, ``__rfloordiv__``,
``__rmod__`` and ``__rdivmod__`` of the :class:`complex` class. They
always raised a :exc:`TypeError`.

- bpo-41902: Micro optimization when compute
:c:member:`~PySequenceMethods.sq_item` and
:c:member:`~PyMappingMethods.mp_subscript` of :class:`range`. Patch by
Dong-hee Na.

- bpo-41894: When loading a native module and a load failure occurs, prevent
a possible UnicodeDecodeError when not running in a UTF-8 locale by
decoding the load error message using the current locale's encoding.

- bpo-41902: Micro optimization for range.index if step is 1. Patch by
Dong-hee Na.

- bpo-41435: Add `sys._current_exceptions()` function to retrieve a
dictionary mapping each thread's identifier to the topmost exception
currently active in that thread at the time the function is called.

- bpo-38605: Enable ``from __future__ import annotations`` (:pep:`563`) by
default. The values found in :attr:`__annotations__` dicts are now
strings, e.g. ``{"x": "int"}`` instead of ``{"x": int}``.

Library
-------

- bpo-35455: On Solaris, :func:`~time.thread_time` is now implemented with
``gethrvtime()`` because ``clock_gettime(CLOCK_THREAD_CPUTIME_ID)`` is not
always available. Patch by Jakub Kulik.

- bpo-42233: The :func:`repr` of :mod:`typing` types containing
:ref:`Generic Alias Types <types-genericalias>` previously did not show
the parameterized types in the ``GenericAlias``. They have now been
changed to do so.

- bpo-29566: ``binhex.binhex()`` consistently writes macOS 9 line endings.

- bpo-26789: The :class:`logging.FileHandler` class now keeps a reference to
the builtin :func:`open` function to be able to open or reopen the file
during Python finalization. Fix errors like: ``NameError: name 'open' is
not defined``. Patch by Victor Stinner.

- bpo-42157: Removed the ``unicodedata.ucnhash_CAPI`` attribute which was an
internal PyCapsule object. The related private ``_PyUnicode_Name_CAPI``
structure was moved to the internal C API. Patch by Victor Stinner.

- bpo-42157: Convert the :mod:`unicodedata` extension module to the
multiphase initialization API (:pep:`489`) and convert the
``unicodedata.UCD`` static type to a heap type. Patch by Mohamed Koubaa
and Victor Stinner.

- bpo-42146: Fix memory leak in :func:`subprocess.Popen` in case an uid
(gid) specified in `user` (`group`, `extra_groups`) overflows `uid_t`
(`gid_t`).

- bpo-42103: :exc:`~plistlib.InvalidFileException` and :exc:`RecursionError`
are now the only errors caused by loading malformed binary Plist file
(previously ValueError and TypeError could be raised in some specific
cases).

- bpo-41490: In ``importlib.resources``, ``.path`` method is more aggressive
about releasing handles to zipfile objects early, enabling use-cases like
certifi to leave the context open but delete the underlying zip file.

- bpo-41052: Pickling heap types implemented in C with protocols 0 and 1
raises now an error instead of producing incorrect data.

- bpo-42089: In ``importlib.metadata.PackageNotFoundError``, make reference
to the package metadata being missing to improve the user experience.

- bpo-41491: plistlib: fix parsing XML plists with hexadecimal integer
values

- bpo-42065: Fix an incorrectly formatted error from
:meth:`_codecs.charmap_decode` when called with a mapped value outside the
range of valid Unicode code points. PR by Max Bernstein.

- bpo-41966: Fix pickling pure Python :class:`datetime.time` subclasses.
Patch by Dean Inwood.

- bpo-19270: :meth:`sched.scheduler.cancel()` will now cancel the correct
event, if two events with same priority are scheduled for the same time.
Patch by Bar Harel.

- bpo-28660: :func:`textwrap.wrap` now attempts to break long words after
hyphens when ``break_long_words=True`` and ``break_on_hyphens=True``.

- bpo-35823: Use ``vfork()`` instead of ``fork()`` for
:func:`subprocess.Popen` on Linux to improve performance in cases where it
is deemed safe.

- bpo-42043: Add support for ``zipfile.Path`` inheritance.
``zipfile.Path.is_file()`` now returns False for non-existent names.
``zipfile.Path`` objects now expose a ``.filename`` attribute and rely on
that to resolve ``.name`` and ``.parent`` when the ``Path`` object is at
the root of the zipfile.

- bpo-42021: Fix possible ref leaks in :mod:`sqlite3` module init.

- bpo-39101: Fixed tests using IsolatedAsyncioTestCase from hanging on
BaseExceptions.

- bpo-41976: Fixed a bug that was causing :func:`ctypes.util.find_library`
to return ``None`` when triying to locate a library in an environment when
gcc>=9 is available and ``ldconfig`` is not. Patch by Pablo Galindo

- bpo-41943: Fix bug where TestCase.assertLogs doesn't correctly filter
messages by level.

- bpo-41923: Implement :pep:`613`, introducing :data:`typing.TypeAlias`
annotation.

- bpo-41905: A new function in abc: *update_abstractmethods* to re-calculate
an abstract class's abstract status. In addition, *dataclass* has been
changed to call this function.

- bpo-23706: Added *newline* parameter to ``pathlib.Path.write_text()``.

- bpo-41876: Tkinter font class repr uses font name

- bpo-41831: ``str()`` for the ``type`` attribute of the ``tkinter.Event``
object always returns now the numeric code returned by Tk instead of the
name of the event type.

- bpo-39337: :func:`encodings.normalize_encoding` now ignores non-ASCII
characters.

- bpo-41747: Ensure all methods that generated from
:func:`dataclasses.dataclass` objects now have the proper ``__qualname__``
attribute referring to the class they belong to. Patch by Batuhan Taskaya.

- bpo-30681: Handle exceptions caused by unparsable date headers when using
email "default" policy. Patch by Tim Bell, Georges Toth

- bpo-41586: Add F_SETPIPE_SZ and F_GETPIPE_SZ to fcntl module. Allow
setting pipesize on subprocess.Popen.

- bpo-41229: Add ``contextlib.aclosing`` for deterministic cleanup of async
generators which is analogous to ``contextlib.closing`` for non-async
generators. Patch by Joongi Kim and John Belmonte.

- bpo-16396: Allow ``ctypes.wintypes`` to be imported on non-Windows
systems.

- bpo-4356: Add a key function to the bisect module.

- bpo-40592: :func:`shutil.which` now ignores empty entries in
:envvar:`PATHEXT` instead of treating them as a match.

- bpo-40492: Fix ``--outfile`` for :mod:`cProfile` / :mod:`profile` not
writing the output file in the original directory when the program being
profiled changes the working directory. PR by Anthony Sottile.

- bpo-34204: The :mod:`shelve` module now uses
:data:`pickle.DEFAULT_PROTOCOL` by default instead of :mod:`pickle`
protocol ``3``.

- bpo-27321: Fixed KeyError exception when flattening an email to a string
attempts to replace a non-existent Content-Transfer-Encoding header.

- bpo-38976: The :mod:`http.cookiejar` module now supports the parsing of
cookies in CURL-style cookiejar files through MozillaCookieJar on all
platforms. Previously, such cookie entries would be silently ignored when
loading a cookiejar with such entries.

Additionally, the HTTP Only attribute is persisted in the object, and will
be correctly written to file if the MozillaCookieJar object is
subsequently dumped.

Documentation
-------------

- bpo-42061: Document __format__ functionality for IP addresses.

- bpo-41910: Document the default implementation of `object.__eq__`.

- bpo-42010: Clarify that subscription expressions are also valid for
certain :term:`classes <class>` and :term:`types <type>` in the standard
library, and for user-defined classes and types if the classmethod
:meth:`__class_getitem__` is provided.

- bpo-41805: Documented :ref:`generic alias type <types-genericalias>` and
:data:`types.GenericAlias`. Also added an entry in glossary for
:term:`generic types <generic type>`.

- bpo-39693: Fix tarfile's extractfile documentation

- bpo-39416: Document some restrictions on the default string
representations of numeric classes.

Tests
-----

- bpo-41739: Fix test_logging.test_race_between_set_target_and_flush(): the
test now waits until all threads complete to avoid leaking running
threads.

- bpo-41970: Avoid a test failure in ``test_lib2to3`` if the module has
already imported at the time the test executes. Patch by Pablo Galindo.

- bpo-41944: Tests for CJK codecs no longer call ``eval()`` on content
received via HTTP.

- bpo-41306: Fixed a failure in ``test_tk.test_widgets.ScaleTest`` happening
when executing the test with Tk 8.6.10.

Build
-----

- bpo-38980: Add ``-fno-semantic-interposition`` to both the compile and
link line when building with ``--enable-optimizations``. Patch by Victor
Stinner and Pablo Galindo.

Windows
-------

- bpo-38439: Updates the icons for IDLE in the Windows Store package.

- bpo-38252: Use 8-byte step to detect ASCII sequence in 64-bit Windows
build.

- bpo-39107: Update Tcl and Tk to 8.6.10 in Windows installer.

- bpo-41557: Update Windows installer to use SQLite 3.33.0.

- bpo-38324: Avoid Unicode errors when accessing certain locale data on
Windows.

macOS
-----

- bpo-41471: Ignore invalid prefix lengths in system proxy excludes.

IDLE
----

- bpo-33987: Mostly finish using ttk widgets, mainly for editor, settings,
and searches. Some patches by Mark Roseman.

- bpo-40511: Typing opening and closing parentheses inside the parentheses
of a function call will no longer cause unnecessary "flashing" off and on
of an existing open call-tip, e.g. when typed in a string literal.

- bpo-38439: Add a 256×256 pixel IDLE icon to the Windows .ico file. Created
by Andrew Clover. Remove the low-color gif variations from the .ico file.

C API
-----

- bpo-42157: The private ``_PyUnicode_Name_CAPI`` structure of the PyCapsule
API ``unicodedata.ucnhash_CAPI`` has been moved to the internal C API.
Patch by Victor Stinner.

- bpo-42015: Fix potential crash in deallocating method objects when
dynamically allocated `PyMethodDef`'s lifetime is managed through the
``self`` argument of a `PyCFunction`.

- bpo-40423: The :mod:`subprocess` module and ``os.closerange`` will now use
the ``close_range(low, high, flags)`` syscall when it is available for
more efficient closing of ranges of descriptors.

- bpo-41845: :c:func:`PyObject_GenericGetDict` is available again in the
limited API when targeting 3.10 or later.

- bpo-40422: Add `_Py_closerange` function to provide performant closing of
a range of file descriptors.

- bpo-41986: :c:data:`Py_FileSystemDefaultEncodeErrors` and
:c:data:`Py_UTF8Mode` are available again in limited API.

- bpo-41756: Add `PyIter_Send` function to allow sending value into
generator/coroutine/iterator without raising StopIteration exception to
signal return.

- bpo-41784: Added ``PyUnicode_AsUTF8AndSize`` to the limited C API.

What's New in Python 3.10.0 alpha 1?
====================================

*Release date: 2020-10-05*

Security
--------

- bpo-41304: Fixes `python3x._pth` being ignored on Windows, caused by the
fix for :issue:`29778` (CVE-2020-15801).

- bpo-41162: Audit hooks are now cleared later during finalization to avoid
missing events.

- bpo-29778: Ensure :file:`python3.dll` is loaded from correct locations
when Python is embedded (CVE-2020-15523).

- bpo-41004: The __hash__() methods of ipaddress.IPv4Interface and
ipaddress.IPv6Interface incorrectly generated constant hash values of 32
and 128 respectively. This resulted in always causing hash collisions. The
fix uses hash() to generate hash values for the tuple of (address, mask
length, network address).

- bpo-39603: Prevent http header injection by rejecting control characters
in http.client.putrequest(...).

Core and Builtins
-----------------

- bpo-41909: Fixed stack overflow in :func:`issubclass` and
:func:`isinstance` when getting the ``__bases__`` attribute leads to
infinite recursion.

- bpo-41922: Speed up calls to ``reversed()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-41873: Calls to ``float()`` are now faster due to the ``vectorcall``
calling convention. Patch by Dennis Sweeney.

- bpo-41870: Speed up calls to ``bool()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-1635741: Port the :mod:`_bisect` module to the multi-phase
initialization API (:pep:`489`).

- bpo-39934: Correctly count control blocks in 'except' in compiler. Ensures
that a syntax error, rather a fatal error, occurs for deeply nested, named
exception handlers.

- bpo-41780: Fix :meth:`__dir__` of :class:`types.GenericAlias`. Patch by
Batuhan Taskaya.

- bpo-1635741: Port the :mod:`_lsprof` extension module to multi-phase
initialization (:pep:`489`).

- bpo-1635741: Port the :mod:`cmath` extension module to multi-phase
initialization (:pep:`489`).

- bpo-1635741: Port the :mod:`_scproxy` extension module to multi-phase
initialization (:pep:`489`).

- bpo-1635741: Port the :mod:`termios` extension module to multi-phase
initialization (:pep:`489`).

- bpo-1635741: Convert the :mod:`_sha256` extension module types to heap
types.

- bpo-41690: Fix a possible stack overflow in the parser when parsing
functions and classes with a huge amount of arguments. Patch by Pablo
Galindo.

- bpo-1635741: Port the :mod:`_overlapped` extension module to multi-phase
initialization (:pep:`489`).

- bpo-1635741: Port the :mod:`_curses_panel` extension module to multi-phase
initialization (:pep:`489`).

- bpo-1635741: Port the :mod:`_opcode` extension module to multi-phase
initialization (:pep:`489`).

- bpo-41681: Fixes the wrong error description in the error raised by using
2 `,` in format string in f-string and :meth:`str.format`.

- bpo-41675: The implementation of :func:`signal.siginterrupt` now uses
:c:func:`sigaction` (if it is available in the system) instead of the
deprecated :c:func:`siginterrupt`. Patch by Pablo Galindo.

- bpo-41670: Prevent line trace being skipped on platforms not compiled with
``USE_COMPUTED_GOTOS``. Fixes issue where some lines nested within a
try-except block were not being traced on Windows.

- bpo-41654: Fix a crash that occurred when destroying subclasses of
:class:`MemoryError`. Patch by Pablo Galindo.

- bpo-1635741: Port the :mod:`zlib` extension module to multi-phase
initialization (:pep:`489`).

- bpo-41631: The ``_ast`` module uses again a global state. Using a module
state per module instance is causing subtle practical problems. For
example, the Mercurial project replaces the ``__import__()`` function to
implement lazy import, whereas Python expected that ``import _ast`` always
return a fully initialized ``_ast`` module.

- bpo-40077: Convert :mod:`_operator` to use :c:func:`PyType_FromSpec`.

- bpo-1653741: Port :mod:`_sha3` to multi-phase init. Convert static types
to heap types.

- bpo-1635741: Port the :mod:`_blake2` extension module to the multi-phase
initialization API (:pep:`489`).

- bpo-41533: Free the stack allocated in ``va_build_stack`` if
``do_mkstack`` fails and the stack is not a ``small_stack``.

- bpo-41531: Fix a bug that was dropping keys when compiling dict literals
with more than 0xFFFF elements. Patch by Pablo Galindo.

- bpo-41525: The output of ``python --help`` contains now only ASCII
characters.

- bpo-1635741: Port the :mod:`_sha1`, :mod:`_sha512`, and :mod:`_md5`
extension modules to multi-phase initialization API (:pep:`489`).

- bpo-41431: Optimize ``dict_merge()`` for copying dict (e.g. ``dict(d)``
and ``{}.update(d)``).

- bpo-41428: Implement PEP 604. This supports (int | str) etc. in place of
Union[str, int].

- bpo-41340: Removed fallback implementation for ``strdup``.

- bpo-38156: Handle interrupts that come after EOF correctly in
``PyOS_StdioReadline``.

- bpo-41342: :func:`round` with integer argument is now faster (9--60%).

- bpo-41334: Constructors :func:`str`, :func:`bytes` and :func:`bytearray`
are now faster (around 30--40% for small objects).

- bpo-41295: Resolve a regression in CPython 3.8.4 where defining
"__setattr__" in a multi-inheritance setup and calling up the hierarchy
chain could fail if builtins/extension types were involved in the base
types.

- bpo-41323: Bytecode optimizations are performed directly on the control
flow graph. This will result in slightly more compact code objects in some
circumstances.

- bpo-41247: Always cache the running loop holder when running
``asyncio.set_running_loop``.

- bpo-41252: Fix incorrect refcounting in _ssl.c's
``_servername_callback()``.

- bpo-1635741: Port :mod:`multiprocessing` to multi-phase initialization

- bpo-1635741: Port :mod:`winapi` to multiphase initialization

- bpo-41215: Use non-NULL default values in the PEG parser keyword list to
overcome a bug that was preventing Python from being properly compiled
when using the XLC compiler. Patch by Pablo Galindo.

- bpo-41218: Python 3.8.3 had a regression where compiling with
ast.PyCF_ALLOW_TOP_LEVEL_AWAIT would aggressively mark list comprehension
with CO_COROUTINE. Now only list comprehension making use of async/await
will tagged as so.

- bpo-1635741: Port :mod:`faulthandler` to multiphase initialization.

- bpo-1635741: Port :mod:`sha256` to multiphase initialization

- bpo-41175: Guard against a NULL pointer dereference within bytearrayobject
triggered by the ``bytearray() + bytearray()`` operation.

- bpo-41100: add arm64 to the allowable Mac OS arches in mpdecimal.h

- bpo-41094: Fix decoding errors with audit when open files with non-ASCII
names on non-UTF-8 locale.

- bpo-39960: The "hackcheck" that prevents sneaking around a type's
__setattr__() by calling the superclass method was rewritten to allow C
implemented heap types.

- bpo-41084: Prefix the error message with 'f-string: ', when parsing an
f-string expression which throws a :exc:`SyntaxError`.

- bpo-40521: Empty frozensets are no longer singletons.

- bpo-41076: Pre-feed the parser with the location of the f-string
expression, not the f-string itself, which allows us to skip the shifting
of the AST node locations after the parsing is completed.

- bpo-41056: Fixes a reference to deallocated stack space during startup
when constructing sys.path involving a relative symlink when code was
supplied via -c. (discovered via Coverity)

- bpo-41061: Fix incorrect expressions and asserts in hashtable code and
tests.

- bpo-41052: Opt out serialization/deserialization for _random.Random

- bpo-40939: Rename `PyPegen*` functions to `PyParser*`, so that we can
remove the old set of `PyParser*` functions that were using the old
parser, but keep everything backwards-compatible.

- bpo-35975: Stefan Behnel reported that cf_feature_version is used even
when PyCF_ONLY_AST is not set. This is against the intention and against
the documented behavior, so it's been fixed.

- bpo-40939: Remove the remaining files from the old parser and the
:mod:`symbol` module.

- bpo-40077: Convert :mod:`_bz2` to use :c:func:`PyType_FromSpec`.

- bpo-41006: The ``encodings.latin_1`` module is no longer imported at
startup. Now it is only imported when it is the filesystem encoding or the
stdio encoding.

- bpo-40636: :func:`zip` now supports :pep:`618`'s ``strict`` parameter,
which raises a :exc:`ValueError` if the arguments are exhausted at
different lengths. Patch by Brandt Bucher.

- bpo-1635741: Port :mod:`_gdbm` to multiphase initialization.

- bpo-40985: Fix a bug that caused the :exc:`SyntaxError` text to be empty
when a file ends with a line ending in a line continuation character (i.e.
backslash). The error text should contain the text of the last line.

- bpo-40958: Fix a possible buffer overflow in the PEG parser when gathering
information for emitting syntax errors. Patch by Pablo Galindo.

- bpo-1635741: Port :mod:`_dbm` to multiphase initialization.

- bpo-40957: Fix refleak in _Py_fopen_obj() when PySys_Audit() fails

- bpo-40950: Add a state to the :mod:`nis` module (:pep:`3121`) and apply
the multiphase initialization. Patch by Dong-hee Na.

- bpo-40947: The Python :ref:`Path Configuration <init-path-config>` now
takes :c:member:`PyConfig.platlibdir` in account.

- bpo-40939: Remove the old parser, the :mod:`parser` module and all
associated support code, command-line options and environment variables.
Patch by Pablo Galindo.

- bpo-40847: Fix a bug where a line with only a line continuation character
is not considered a blank line at tokenizer level. In such cases, more
than a single `NEWLINE` token was emitted. The old parser was working
around the issue, but the new parser threw a :exc:`SyntaxError` for valid
input due to this. For example, an empty line following a line
continuation character was interpreted as a :exc:`SyntaxError`.

- bpo-40890: Each dictionary view now has a ``mapping`` attribute that
provides a :class:`types.MappingProxyType` wrapping the original
dictionary. Patch contributed by Dennis Sweeney.

- bpo-40889: Improved the performance of symmetric difference operations on
dictionary item views. Patch by Dennis Sweeney.

- bpo-40904: Fix possible segfault in the new PEG parser when parsing
f-string containing yield statements with no value (:code:`f"{yield}"`).
Patch by Pablo Galindo

- bpo-40903: Fixed a possible segfault in the new PEG parser when producing
error messages for invalid assignments of the form :code:`p=p=`. Patch by
Pablo Galindo

- bpo-40880: Fix invalid memory read in the new parser when checking
newlines in string literals. Patch by Pablo Galindo.

- bpo-40883: Fix memory leak in when parsing f-strings in the new parser.
Patch by Pablo Galindo

- bpo-40870: Raise :exc:`ValueError` when validating custom AST's where the
constants ``True``, ``False`` and ``None`` are used within a
:class:`ast.Name` node.

- bpo-40854: Allow overriding :data:`sys.platlibdir` via a new
:envvar:`PYTHONPLATLIBDIR` environment variable.

- bpo-40826: Fix GIL usage in :c:func:`PyOS_Readline`: lock the GIL to set
an exception and pass the Python thread state when checking if there is a
pending signal.

- bpo-1635741: Port :mod:`fcntl` to multiphase initialization.

- bpo-19468: Delete unnecessary instance check in importlib.reload(). Patch
by Furkan Önder.

- bpo-40824: Unexpected errors in calling the ``__iter__`` method are no
longer masked by ``TypeError`` in the :keyword:`in` operator and functions
:func:`~operator.contains`, :func:`~operator.indexOf` and
:func:`~operator.countOf` of the :mod:`operator` module.

- bpo-40792: Attributes ``start``, ``stop`` and ``step`` of the
:class:`range` object now always has exact type :class:`int`. Previously,
they could have been an instance of a subclass of ``int``.

- bpo-40780: Fix a corner case where g-style string formatting of a float
failed to remove trailing zeros.

- bpo-38964: When there's a :exc:`SyntaxError` in the expression part of an
fstring, the filename attribute of the :exc:`SyntaxError` gets correctly
set to the name of the file the fstring resides in.

- bpo-40750: Support the "-d" debug flag in the new PEG parser. Patch by
Pablo Galindo

- bpo-40217: Instances of types created with
:c:func:`PyType_FromSpecWithBases` will no longer automatically visit
their class object when traversing references in the garbage collector.
The user is expected to manually visit the object's class. Patch by Pablo
Galindo.

- bpo-39573: :c:func:`Py_TYPE()` is changed to the inline static function.
Patch by Dong-hee Na.

- bpo-40696: Fix a hang that can arise after :meth:`generator.throw` due to
a cycle in the exception context chain.

- bpo-40521: Each interpreter now its has own free lists, singletons and
caches:

* Free lists: float, tuple, list, dict, frame, context,
asynchronous generator, MemoryError.
* Singletons: empty tuple, empty bytes string, empty Unicode string,
single byte character, single Unicode (latin1) character.
* Slice cache.

They are no longer shared by all interpreters.

- bpo-40679: Certain :exc:`TypeError` messages about missing or extra
arguments now include the function's :term:`qualified name`. Patch by
Dennis Sweeney.

- bpo-29590: Make the stack trace correct after calling
:meth:`generator.throw` on a generator that has yielded from a ``yield
from``.

- bpo-4022: Improve performance of generators by not raising internal
StopIteration.

- bpo-1635741: Port :mod:`mmap` to multiphase initialization.

- bpo-1635741: Port :mod:`_lzma` to multiphase initialization.

- bpo-37999: Builtin and extension functions that take integer arguments no
longer accept :class:`~decimal.Decimal`\ s, :class:`~fractions.Fraction`\
s and other objects that can be converted to integers only with a loss
(e.g. that have the :meth:`~object.__int__` method but do not have the
:meth:`~object.__index__` method).

- bpo-29882: Add :meth:`int.bit_count()`, counting the number of ones in the
binary representation of an integer. Patch by Niklas Fiekas.

- bpo-36982: Use ncurses extended color functions when available to support
terminals with 256 colors, and add the new function
:func:`curses.has_extended_color_support` to indicate whether extended
color support is provided by the underlying ncurses library.

- bpo-19569: Add the private macros ``_Py_COMP_DIAG_PUSH``,
``_Py_COMP_DIAG_IGNORE_DEPR_DECLS``, and ``_Py_COMP_DIAG_POP``.

- bpo-26680: The int type now supports the x.is_integer() method for
compatibility with float.

Library
-------

- bpo-41900: C14N 2.0 serialisation in xml.etree.ElementTree failed for
unprefixed attributes when a default namespace was defined.

- bpo-41887: Strip leading spaces and tabs on :func:`ast.literal_eval`. Also
document stripping of spaces and tabs for :func:`eval`.

- bpo-41773: Note in documentation that :func:`random.choices` doesn't
support non-finite weights, raise :exc:`ValueError` when given non-finite
weights.

- bpo-41840: Fix a bug in the :mod:`symtable` module that was causing
module-scope global variables to not be reported as both local and global.
Patch by Pablo Galindo.

- bpo-41842: Add :func:`codecs.unregister` function to unregister a codec
search function.

- bpo-40564: In ``zipfile.Path``, mutate the passed ZipFile object type
instead of making a copy. Prevents issues when both the local copy and the
caller’s copy attempt to close the same file handle.

- bpo-40670: More reliable validation of statements in
:class:`timeit.Timer`. It now accepts "empty" statements (only whitespaces
and comments) and rejects misindentent statements.

- bpo-41833: The :class:`threading.Thread` constructor now uses the target
name if the *target* argument is specified but the *name* argument is
omitted.

- bpo-41817: fix `tkinter.EventType` Enum so all members are strings, and
none are tuples

- bpo-41810: :data:`types.EllipsisType`, :data:`types.NotImplementedType`
and :data:`types.NoneType` have been reintroduced, providing a new set of
types readily interpretable by static type checkers.

- bpo-41815: Fix SQLite3 segfault when backing up closed database. Patch
contributed by Peter David McCormick.

- bpo-41816: StrEnum added: it ensures that all members are already strings
or string candidates

- bpo-41517: fix bug allowing Enums to be extended via multiple inheritance

- bpo-39587: use the correct mix-in data type when constructing Enums

- bpo-41792: Add is_typeddict function to typing.py to check if a type is a
TypedDict class

Previously there was no way to check that without using private API. See
the `relevant issue in python/typing
<https://github.com/python/typing/issues/751>`

- bpo-41789: Honor `object` overrides in `Enum` class creation
(specifically, `__str__`, `__repr__`, `__format__`, and `__reduce_ex__`).

- bpo-32218: `enum.Flag` and `enum.IntFlag` members are now iterable

- bpo-39651: Fix a race condition in the ``call_soon_threadsafe()`` method
of ``asyncio.ProactorEventLoop``: do nothing if the self-pipe socket has
been closed.

- bpo-1635741: Port the ``mashal`` extension module to the multi-phase
initialization API (:pep:`489`).

- bpo-1635741: Port the ``_string`` extension module to the multi-phase
initialization API (:pep:`489`).

- bpo-41732: Added an :term:`iterator` to :class:`memoryview`.

- bpo-41720: Fixed :meth:`turtle.Vec2D.__rmul__` for arguments which are not
int or float.

- bpo-41696: Fix handling of debug mode in :func:`asyncio.run`. This allows
setting ``PYTHONASYNCIODEBUG`` or ``-X dev`` to enable asyncio debug mode
when using :func:`asyncio.run`.

- bpo-41687: Fix implementation of sendfile to be compatible with Solaris.

- bpo-41662: No longer override exceptions raised in ``__len__()`` of a
sequence of parameters in :mod:`sqlite3` with
:exc:`~sqlite3.ProgrammingError`.

- bpo-39010: Restarting a ``ProactorEventLoop`` on Windows no longer logs
spurious ``ConnectionResetErrors``.

- bpo-41638: :exc:`~sqlite3.ProgrammingError` message for absent parameter
in :mod:`sqlite3` contains now the name of the parameter instead of its
index when parameters are supplied as a dict.

- bpo-41662: Fixed crash when mutate list of parameters during iteration in
:mod:`sqlite3`.

- bpo-41513: Improved the accuracy of math.hypot(). Internally, each step
is computed with extra precision so that the result is now almost always
correctly rounded.

- bpo-41609: The pdb whatis command correctly reports instance methods as
'Method' rather than 'Function'.

- bpo-39994: Fixed pprint's handling of dict subclasses that override
__repr__.

- bpo-32751: When cancelling the task due to a timeout,
:meth:`asyncio.wait_for` will now wait until the cancellation is complete
also in the case when *timeout* is <= 0, like it does with positive
timeouts.

- bpo-37658: :meth:`asyncio.wait_for` now properly handles races between
cancellation of itself and the completion of the wrapped awaitable.

- bpo-40782: Change the method asyncio.AbstractEventLoop.run_in_executor to
not be a coroutine.

- bpo-41520: Fix :mod:`codeop` regression that prevented turning compile
warnings into errors.

- bpo-41528: turtle uses math module functions to convert degrees to radians
and vice versa and to calculate vector norm

- bpo-41513: Minor algorithmic improvement to math.hypot() and math.dist()
giving small gains in speed and accuracy.

- bpo-41503: Fixed a race between setTarget and flush in
logging.handlers.MemoryHandler.

- bpo-41497: Fix potential UnicodeDecodeError in dis module.

- bpo-41467: On Windows, fix asyncio ``recv_into()`` return value when the
socket/pipe is closed (:exc:`BrokenPipeError`): return ``0`` rather than
an empty byte string (``b''``).

- bpo-41425: Make tkinter doc example runnable.

- bpo-41421: Make an algebraic simplification to random.paretovariate(). It
now is slightly less subject to round-off error and is slightly faster.
Inputs that used to cause ZeroDivisionError now cause an OverflowError
instead.

- bpo-41440: Add :func:`os.cpu_count()` support for VxWorks RTOS.

- bpo-41316: Fix the :mod:`tarfile` module to write only basename of TAR
file to GZIP compression header.

- bpo-41384: Raise TclError instead of TypeError when an unknown option is
passed to tkinter.OptionMenu.

- bpo-41317: Use add_done_callback() in asyncio.loop.sock_accept() to
unsubscribe reader early on cancellation.

- bpo-41364: Reduce import overhead of :mod:`uuid`.

- bpo-35328: Set the environment variable ``VIRTUAL_ENV_PROMPT`` at
:mod:`venv` activation.

- bpo-41341: Recursive evaluation of `typing.ForwardRef` in
`get_type_hints`.

- bpo-41344: Prevent creating :class:`shared_memory.SharedMemory` objects
with :code:`size=0`.

- bpo-41333: :meth:`collections.OrderedDict.pop` is now 2 times faster.

- bpo-41288: Unpickling invalid NEWOBJ_EX opcode with the C implementation
raises now UnpicklingError instead of crashing.

- bpo-39017: Avoid infinite loop when reading specially crafted TAR files
using the tarfile module (CVE-2019-20907).

- bpo-41273: Speed up any transport using ``_ProactorReadPipeTransport`` by
calling ``recv_into`` instead of ``recv``, thus not creating a new buffer
for each ``recv`` call in the transport's read loop.

- bpo-41235: Fix the error handling in
:meth:`ssl.SSLContext.load_dh_params`.

- bpo-41207: In distutils.spawn, restore expectation that DistutilsExecError
is raised when the command is not found.

- bpo-29727: Register :class:`array.array` as a
:class:`~collections.abc.MutableSequence`. Patch by Pablo Galindo.

- bpo-39168: Remove the ``__new__`` method of :class:`typing.Generic`.

- bpo-41194: Fix a crash in the ``_ast`` module: it can no longer be loaded
more than once. It now uses a global state rather than a module state.

- bpo-41195: Add read-only ssl.SSLContext.security_level attribute to
retrieve the context's security level.

- bpo-41193: The ``write_history()`` atexit function of the readline
completer now ignores any :exc:`OSError` to ignore error if the filesystem
is read-only, instead of only ignoring :exc:`FileNotFoundError` and
:exc:`PermissionError`.

- bpo-41182: selector: use DefaultSelector based upon implementation

- bpo-41161: The decimal module now requires libmpdec-2.5.0. Users of
--with-system-libmpdec should update their system library.

- bpo-40874: The decimal module now requires libmpdec-2.5.0.

- bpo-41138: Fixed the :mod:`trace` module CLI for Python source files with
non-UTF-8 encoding.

- bpo-31082: Use the term "iterable" in the docstring for
:func:`functools.reduce`.

- bpo-40521: Remove freelist from collections.deque().

- bpo-31938: Fix default-value signatures of several functions in the
:mod:`select` module - by Anthony Sottile.

- bpo-41068: Fixed reading files with non-ASCII names from ZIP archive
directly after writing them.

- bpo-41058: :func:`pdb.find_function` now correctly determines the source
file encoding.

- bpo-41056: Invalid file descriptor values are now prevented from being
passed to os.fpathconf. (discovered by Coverity)

- bpo-41056: Fix a NULL pointer dereference within the ssl module during a
MemoryError in the keylog callback. (discovered by Coverity)

- bpo-41056: Fixed an instance where a MemoryError within the zoneinfo
module might not be reported or not reported at its source. (found by
Coverity)

- bpo-41048: :func:`mimetypes.read_mime_types` function reads the rule file
using UTF-8 encoding, not the locale encoding. Patch by Srinivas Reddy
Thatiparthy.

- bpo-41043: Fixed the use of :func:`~glob.glob` in the stdlib: literal part
of the path is now always correctly escaped.

- bpo-41025: Fixed an issue preventing the C implementation of
:class:`zoneinfo.ZoneInfo` from being subclassed.

- bpo-35018: Add the :class:`xml.sax.handler.LexicalHandler` class that is
present in other SAX XML implementations.

- bpo-41002: Improve performance of HTTPResponse.read with a given amount.
Patch by Bruce Merry.

- bpo-40448: :mod:`ensurepip` now disables the use of `pip` cache when
installing the bundled versions of `pip` and `setuptools`. Patch by
Krzysztof Konopko.

- bpo-40967: Removed :meth:`asyncio.Task.current_task` and
:meth:`asyncio.Task.all_tasks`. Patch contributed by Rémi Lapeyre.

- bpo-40924: Ensure ``importlib.resources.path`` returns an extant path for
the SourceFileLoader's resource reader. Avoids the regression identified
in master while a long-term solution is devised.

- bpo-40955: Fix a minor memory leak in :mod:`subprocess` module when
extra_groups was specified.

- bpo-40855: The standard deviation and variance functions in the statistics
module were ignoring their mu and xbar arguments.

- bpo-40939: Use the new PEG parser when generating the stdlib
:mod:`keyword` module.

- bpo-23427: Add :data:`sys.orig_argv` attribute: the list of the original
command line arguments passed to the Python executable.

- bpo-33689: Ignore empty or whitespace-only lines in .pth files. This
matches the documentated behavior. Before, empty lines caused the
site-packages dir to appear multiple times in sys.path. By Ido Michael,
contributors Malcolm Smith and Tal Einat.

- bpo-40884: Added a `defaults` parameter to :class:`logging.Formatter`, to
allow specifying default values for custom fields. Patch by Asaf Alon and
Bar Harel.

- bpo-40876: Clarify error message in the :mod:`csv` module.

- bpo-39791: Refresh importlib.metadata from importlib_metadata 1.6.1.

- bpo-40807: Stop codeop._maybe_compile, used by code.InteractiveInterpreter
(and IDLE). from emitting each warning three times.

- bpo-32604: Fix reference leak in the :mod:`select` module when the module
is imported in a subinterpreter.

- bpo-39791: Built-in loaders (SourceFileLoader and ZipImporter) now supply
``TraversableResources`` implementations for ``ResourceReader``, and the
fallback function has been removed.

- bpo-39314: :class:`rlcompleter.Completer` and the standard Python shell
now close the parenthesis for functions that take no arguments. Patch
contributed by Rémi Lapeyre.

- bpo-17005: The topological sort functionality that was introduced
initially in the :mod:`functools` module has been moved to a new
:mod:`graphlib` module to better accommodate the new tools and keep the
original scope of the :mod:`functools` module. Patch by Pablo Galindo

- bpo-40834: Fix truncate when sending str object
with_xxsubinterpreters.channel_send.

- bpo-40755: Add rich comparisons to collections.Counter().

- bpo-26407: Unexpected errors in calling the ``__iter__`` method are no
longer masked by ``TypeError`` in :func:`csv.reader`,
:func:`csv.writer.writerow` and :meth:`csv.writer.writerows`.

- bpo-39384: Fixed email.contentmanager to allow set_content() to set a null
string.

- bpo-40744: The :mod:`sqlite3` module uses SQLite API functions that
require SQLite v3.7.3 or higher. This patch removes support for older
SQLite versions, and explicitly requires SQLite 3.7.3 both at build,
compile and runtime. Patch by Sergey Fedoseev and Erlend E. Aasland.

- bpo-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time
to avoid errors on some compilers.

- bpo-38488: Update ensurepip to install pip 20.1.1 and setuptools 47.1.0.

- bpo-40792: The result of :func:`operator.index` now always has exact type
:class:`int`. Previously, the result could have been an instance of a
subclass of ``int``.

- bpo-40767: :mod:`webbrowser` now properly finds the default browser in
pure Wayland systems by checking the WAYLAND_DISPLAY environment variable.
Patch contributed by Jérémy Attali.

- bpo-40791: :func:`hashlib.compare_digest` uses OpenSSL's
``CRYPTO_memcmp()`` function when OpenSSL is available.

- bpo-40795: :mod:`ctypes` module: If ctypes fails to convert the result of
a callback or if a ctypes callback function raises an exception,
sys.unraisablehook is now called with an exception set. Previously, the
error was logged into stderr by :c:func:`PyErr_Print`.

- bpo-16995: Add :func:`base64.b32hexencode` and :func:`base64.b32hexdecode`
to support the Base32 Encoding with Extended Hex Alphabet.

- bpo-30008: Fix :mod:`ssl` code to be compatible with OpenSSL 1.1.x builds
that use ``no-deprecated`` and ``--api=1.1.0``.

- bpo-30064: Fix asyncio ``loop.sock_*`` race condition issue

- bpo-40759: Deprecate the :mod:`symbol` module.

- bpo-40756: The second argument (extra) of ``LoggerAdapter.__init__`` now
defaults to None.

- bpo-37129: Add a new :data:`os.RWF_APPEND` flag for :func:`os.pwritev`.

- bpo-40737: Fix possible reference leak for :mod:`sqlite3` initialization.

- bpo-40726: Handle cases where the ``end_lineno`` is ``None`` on
:func:`ast.increment_lineno`.

- bpo-40698: :mod:`distutils` upload creates SHA2-256 and Blake2b-256
digests. MD5 digests is skipped if platform blocks MD5.

- bpo-40695: :mod:`hashlib` no longer falls back to builtin hash
implementations when OpenSSL provides a hash digest and the algorithm is
blocked by security policy.

- bpo-9216: func:`hashlib.new` passed ``usedforsecurity`` to OpenSSL EVP
constructor ``_hashlib.new()``. test_hashlib and test_smtplib handle
strict security policy better.

- bpo-40614: :func:`ast.parse` will not parse self documenting expressions
in f-strings when passed ``feature_version`` is less than ``(3, 8)``.

- bpo-40626: Add h5 file extension as MIME Type application/x-hdf5, as per
HDF Group recommendation for HDF5 formatted data files. Patch contributed
by Mark Schwab.

- bpo-25920: On macOS, when building Python for macOS 10.4 and older, which
wasn't the case for python.org macOS installer, :func:`socket.getaddrinfo`
no longer uses an internal lock to prevent race conditions when calling
``getaddrinfo()`` which is thread-safe since macOS 10.5. Python 3.9
requires macOS 10.6 or newer. The internal lock caused random hang on fork
when another thread was calling :func:`socket.getaddrinfo`. The lock was
also used on FreeBSD older than 5.3, OpenBSD older than 201311 and NetBSD
older than 4.

- bpo-40671: Prepare ``_hashlib`` for :pep:`489` and use
:c:func:`PyModule_AddType`.

- bpo-32309: Added a new :term:`coroutine` :func:`asyncio.to_thread`. It is
mainly used for running IO-bound functions in a separate thread to avoid
blocking the event loop, and essentially works as a high-level version of
:meth:`~asyncio.loop.run_in_executor` that can directly take keyword
arguments.

- bpo-36543: Restored the deprecated :mod:`xml.etree.cElementTree` module.

- bpo-40611: :data:`~mmap.MAP_POPULATE` constant has now been added to the
list of exported :mod:`mmap` module flags.

- bpo-39881: PEP 554 for use in the test suite. (Patch By Joannah Nanjekye)

- bpo-13097: ``ctypes`` now raises an ``ArgumentError`` when a callback is
invoked with more than 1024 arguments.

- bpo-39385: A new test assertion context-manager,
:func:`unittest.assertNoLogs` will ensure a given block of code emits no
log messages using the logging module. Contributed by Kit Yan Choi.

- bpo-23082: Updated the error message and docs of PurePath.relative_to() to
better reflect the function behaviour.

- bpo-40318: Use SQLite3 trace v2 API, if it is available.

- bpo-40105: ZipFile truncates files to avoid corruption when a shorter
comment is provided in append ("a") mode. Patch by Jan Mazur.

- bpo-40084: Fix ``Enum.__dir__``: dir(Enum.member) now includes attributes
as well as methods.

- bpo-31122: ssl.wrap_socket() now raises ssl.SSLEOFError rather than
OSError when peer closes connection during TLS negotiation

- bpo-39728: fix default `_missing_` so a duplicate `ValueError` is not set
as the `__context__` of the original `ValueError`

- bpo-39244: Fixed :class:`multiprocessing.context.get_all_start_methods` to
properly return the default method first on macOS.

- bpo-39040: Fix parsing of invalid mime headers parameters by collapsing
whitespace between encoded words in a bare-quote-string.

- bpo-38731: Add ``--quiet`` option to command-line interface of
:mod:`py_compile`. Patch by Gregory Schevchenko.

- bpo-35714: :exc:`struct.error` is now raised if there is a null character
in a :mod:`struct` format string.

- bpo-38144: Added the *root_dir* and *dir_fd* parameters in
:func:`glob.glob`.

- bpo-26543: Fix :meth:`IMAP4.noop()` when debug mode is enabled (ex:
``imaplib.Debug = 3``).

- bpo-12178: :func:`csv.writer` now correctly escapes *escapechar* when
input contains *escapechar*. Patch by Catalin Iacob, Berker Peksag, and
Itay Elbirt.

- bpo-36290: AST nodes are now raising :exc:`TypeError` on conflicting
keyword arguments. Patch contributed by Rémi Lapeyre.

- bpo-33944: Added site.py site-packages tracing in verbose mode.

- bpo-35078: Refactor formatweekday, formatmonthname methods in
LocaleHTMLCalendar and LocaleTextCalendar classes in calendar module to
call the base class methods.This enables customizable CSS classes for
LocaleHTMLCalendar. Patch by Srinivas Reddy Thatiparthy

- bpo-29620: :func:`~unittest.TestCase.assertWarns` no longer raises a
``RuntimeException`` when accessing a module's ``__warningregistry__``
causes importation of a new module, or when a new module is imported in
another thread. Patch by Kernc.

- bpo-31844: Remove ``ParserBase.error()`` method from the private and
undocumented ``_markupbase`` module. :class:`html.parser.HTMLParser` is
the only subclass of ``ParserBase`` and its ``error()`` implementation was
deprecated in Python 3.4 and removed in Python 3.5.

- bpo-34226: Fix `cgi.parse_multipart` without content_length. Patch by
Roger Duran

- bpo-33660: Fix pathlib.PosixPath to resolve a relative path located on the
root directory properly.

- bpo-28557: Improve the error message for a misbehaving ``rawio.readinto``

- bpo-26680: The d.is_integer() method is added to the Decimal type, for
compatibility with other number types.

- bpo-26680: The x.is_integer() method is incorporated into the abstract
types of the numeric tower, Real, Rational and Integral, with appropriate
default implementations.

Documentation
-------------

- bpo-41428: Add documentation for :pep:`604` (Allow writing union types as
``X | Y``).

- bpo-41774: In Programming FAQ "Sequences (Tuples/Lists)" section, add "How
do you remove multiple items from a list".

- bpo-35293: Fix RemovedInSphinx40Warning when building the documentation.
Patch by Dong-hee Na.

- bpo-37149: Change Shipman tkinter doc link from archive.org to TkDocs.
(The doc has been removed from the NMT server.) The new link responds
much faster and includes a short explanatory note.

- bpo-41726: Update the refcounts info of ``PyType_FromModuleAndSpec``.

- bpo-41624: Fix the signature of :class:`typing.Coroutine`.

- bpo-40204: Enable Sphinx 3.2 ``c_allow_pre_v3`` option and disable
``c_warn_on_allowed_pre_v3`` option to make the documentation compatible
with Sphinx 2 and Sphinx 3.

- bpo-41045: Add documentation for debug feature of f-strings.

- bpo-41314: Changed the release when ``from __future__ import annotations``
becomes the default from ``4.0`` to ``3.10`` (following a change in PEP
563).

- bpo-40979: Refactored typing.rst, arranging more than 70 classes,
functions, and decorators into new sub-sections.

- bpo-40552: Fix in tutorial section 4.2. Code snippet is now correct.

- bpo-39883: Make code, examples, and recipes in the Python documentation be
licensed under the more permissive BSD0 license in addition to the
existing Python 2.0 license.

- bpo-37703: Updated Documentation to comprehensively elaborate on the
behaviour of gather.cancel()

Tests
-----

- bpo-41939: Fix test_site.test_license_exists_at_url(): call
``urllib.request.urlcleanup()`` to reset the global
``urllib.request._opener``. Patch by Victor Stinner.

- bpo-41731: Make test_cmd_line_script pass with option '-vv'.

- bpo-41602: Add tests for SIGINT handling in the runpy module.

- bpo-41521: :mod:`test.support`: Rename ``blacklist`` parameter of
:func:`~test.support.check__all__` to ``not_exported``.

- bpo-41477: Make ctypes optional in test_genericalias.

- bpo-41085: Fix integer overflow in the :meth:`array.array.index` method on
64-bit Windows for index larger than ``2**31``.

- bpo-41069: :data:`test.support.TESTFN` and the current directory for tests
when run via ``test.regrtest`` contain now non-ascii characters if
possible.

- bpo-38377: On Linux, skip tests using multiprocessing if the current user
cannot create a file in ``/dev/shm/`` directory. Add the
:func:`~test.support.skip_if_broken_multiprocessing_synchronize` function
to the :mod:`test.support` module.

- bpo-41009: Fix use of ``support.require_{linux|mac|freebsd}_version()``
decorators as class decorator.

- bpo-41003: Fix ``test_copyreg`` when ``numpy`` is installed:
``test.pickletester`` now saves/restores warnings filters when importing
``numpy``, to ignore filters installed by ``numpy``.

- bpo-40964: Disable remote :mod:`imaplib` tests, host cyrus.andrew.cmu.edu
is blocking incoming connections.

- bpo-40927: Fix test_binhex when run twice: it now uses
import_fresh_module() to ensure that it raises DeprecationWarning each
time.

- bpo-17258: Skip some :mod:`multiprocessing` tests when MD5 hash digest is
blocked.

- bpo-31904: Increase LOOPBACK_TIMEOUT to 10 for VxWorks RTOS.

- bpo-38169: Increase code coverage for SharedMemory and ShareableList

- bpo-34401: Make test_gdb properly run on HP-UX. Patch by Michael Osipov.

Build
-----

- bpo-38249: Update :c:macro:`Py_UNREACHABLE` to use __builtin_unreachable()
if only the compiler is able to use it. Patch by Dong-hee Na.

- bpo-41617: Fix ``pycore_bitutils.h`` header file to support old clang
versions: ``__builtin_bswap16()`` is not available in LLVM clang 3.0.

- bpo-40204: Pin Sphinx version to 2.3.1 in ``Doc/Makefile``.

- bpo-36020: The C99 functions :c:func:`snprintf` and :c:func:`vsnprintf`
are now required to build Python.

- bpo-40684: ``make install`` now uses the ``PLATLIBDIR`` variable for the
destination ``lib-dynload/`` directory when ``./configure
--with-platlibdir`` is used.

- bpo-40683: Fixed an issue where the :mod:`zoneinfo` module and its tests
were not included when Python is installed with ``make``.

Windows
-------

- bpo-41744: Fixes automatic import of props file when using the Nuget
package.

- bpo-41627: The user site directory for 32-bit now includes a ``-32``
suffix to distinguish it from the 64-bit interpreter's directory.

- bpo-41526: Fixed layout of final page of the installer by removing the
special thanks to Mark Hammond (with his permission).

- bpo-41492: Fixes the description that appears in UAC prompts.

- bpo-40948: Improve post-install message to direct people to the "py"
command.

- bpo-41412: The installer will now fail to install on Windows 7 and Windows
8. Further, the UCRT dependency is now always downloaded on demand.

- bpo-40741: Update Windows release to include SQLite 3.32.3.

- bpo-41142: :mod:`msilib` now supports creating CAB files with non-ASCII
file path and adding files with non-ASCII file path to them.

- bpo-41074: Fixed support of non-ASCII names in functions
:func:`msilib.OpenDatabase` and :func:`msilib.init_database` and non-ASCII
SQL in method :meth:`msilib.Database.OpenView`.

- bpo-41039: Stable ABI redirection DLL (python3.dll) now uses ``#pragma
comment(linker)`` for re-exporting.

- bpo-40164: Updates Windows OpenSSL to 1.1.1g

- bpo-39631: Changes the registered MIME type for ``.py`` files on Windows
to ``text/x-python`` instead of ``text/plain``.

- bpo-40677: Manually define IO_REPARSE_TAG_APPEXECLINK in case some old
Windows SDK doesn't have it.

- bpo-37556: Extend py.exe help to mention overrides via venv, shebang,
environmental variables & ini files.

macOS
-----

- bpo-41557: Update macOS installer to use SQLite 3.33.0.

- bpo-39580: Avoid opening Finder window if running installer from the
command line. Patch contributed by Rick Heil.

- bpo-41100: Fix configure error when building on macOS 11. Note that the
current Python release was released shortly after the first developer
preview of macOS 11 (Big Sur); there are other known issues with building
and running on the developer preview. Big Sur is expected to be fully
supported in a future bugfix release of Python 3.8.x and with 3.9.0.

- bpo-40741: Update macOS installer to use SQLite 3.32.3.

- bpo-41005: fixed an XDG settings issue not allowing macos to open browser
in webbrowser.py

- bpo-40741: Update macOS installer to use SQLite 3.32.2.

IDLE
----

- bpo-41775: Use 'IDLE Shell' as shell title

- bpo-35764: Rewrite the Calltips doc section.

- bpo-40181: In calltips, stop reminding that '/' marks the end of
positional-only arguments.

- bpo-41468: Improve IDLE run crash error message (which users should never
see).

- bpo-41373: Save files loaded with no line ending, as when blank, or
different line endings, by setting its line ending to the system default.
Fix regression in 3.8.4 and 3.9.0b4.

- bpo-41300: Save files with non-ascii chars. Fix regression released in
3.9.0b4 and 3.8.4.

- bpo-37765: Add keywords to module name completion list. Rewrite
Completions section of IDLE doc.

- bpo-41152: The encoding of ``stdin``, ``stdout`` and ``stderr`` in IDLE is
now always UTF-8.

- bpo-41144: Make Open Module open a special module such as os.path.

- bpo-39885: Make context menu Cut and Copy work again when right-clicking
within a selection.

- bpo-40723: Make test_idle pass when run after import.

C API
-----

- bpo-41936: Removed undocumented macros ``Py_ALLOW_RECURSION`` and
``Py_END_ALLOW_RECURSION`` and the ``recursion_critical`` field of the
:c:type:`PyInterpreterState` structure.

- bpo-41692: The ``PyUnicode_InternImmortal()`` function is now deprecated
and will be removed in Python 3.12: use :c:func:`PyUnicode_InternInPlace`
instead. Patch by Victor Stinner.

- bpo-41842: Add :c:func:`PyCodec_Unregister` function to unregister a codec
search function.

- bpo-41834: Remove the ``_Py_CheckRecursionLimit`` variable: it has been
replaced by ``ceval.recursion_limit`` of the :c:type:`PyInterpreterState`
structure. Patch by Victor Stinner.

- bpo-41689: Types created with :c:func:`PyType_FromSpec` now make any
signature in their ``tp_doc`` slot accessible from ``__text_signature__``.

- bpo-41524: Fix bug in PyOS_mystrnicmp and PyOS_mystricmp that incremented
pointers beyond the end of a string.

- bpo-41324: Add a minimal decimal capsule API. The API supports fast
conversions between Decimals up to 38 digits and their triple
representation as a C struct.

- bpo-30155: Add :c:func:`PyDateTime_DATE_GET_TZINFO` and
:c:func:`PyDateTime_TIME_GET_TZINFO` macros for accessing the ``tzinfo``
attributes of :class:`datetime.datetime` and :class:`datetime.time`
objects.

- bpo-40170: Revert :c:func:`PyType_HasFeature` change: it reads again
directly the :c:member:`PyTypeObject.tp_flags` member when the limited C
API is not used, rather than always calling :c:func:`PyType_GetFlags`
which hides implementation details.

- bpo-41123: Remove ``PyUnicode_AsUnicodeCopy``.

- bpo-41123: Removed ``PyLong_FromUnicode()``.

- bpo-41123: Removed ``PyUnicode_GetMax()``.

- bpo-41123: Removed ``Py_UNICODE_str*`` functions manipulating
``Py_UNICODE*`` strings.

- bpo-41103: ``PyObject_AsCharBuffer()``, ``PyObject_AsReadBuffer()``,
``PyObject_CheckReadBuffer()``, and ``PyObject_AsWriteBuffer()`` are
removed. Please migrate to new buffer protocol;
:c:func:`PyObject_GetBuffer` and :c:func:`PyBuffer_Release`.

- bpo-36346: Raises DeprecationWarning for ``PyUnicode_FromUnicode(NULL,
size)`` and ``PyUnicode_FromStringAndSize(NULL, size)`` with ``size > 0``.

- bpo-36346: Mark ``Py_UNICODE_COPY``, ``Py_UNICODE_FILL``,
``PyUnicode_WSTR_LENGTH``, ``PyUnicode_FromUnicode``,
``PyUnicode_AsUnicode``, and ``PyUnicode_AsUnicodeAndSize`` as deprecated
in C. Remove ``Py_UNICODE_MATCH`` which was deprecated and broken since
Python 3.3.

- bpo-40989: The :c:func:`PyObject_INIT` and :c:func:`PyObject_INIT_VAR`
macros become aliases to, respectively, :c:func:`PyObject_Init` and
:c:func:`PyObject_InitVar` functions.

- bpo-36020: On Windows, ``#include "pyerrors.h"`` no longer defines
``snprintf`` and ``vsnprintf`` macros.

- bpo-40943: The ``PY_SSIZE_T_CLEAN`` macro must now be defined to use
:c:func:`PyArg_ParseTuple` and :c:func:`Py_BuildValue` formats which use
``#``: ``es#``, ``et#``, ``s#``, ``u#``, ``y#``, ``z#``, ``U#`` and
``Z#``. See :ref:`Parsing arguments and building values <arg-parsing>` and
the :pep:`353`.

- bpo-40910: Export explicitly the :c:func:`Py_GetArgcArgv` function to the
C API and document the function. Previously, it was exported implicitly
which no longer works since Python is built with ``-fvisibility=hidden``.

- bpo-40724: Allow defining buffer slots in type specs.

- bpo-40679: Fix a ``_PyEval_EvalCode()`` crash if *qualname* argument is
NULL.

- bpo-40839: Calling :c:func:`PyDict_GetItem` without :term:`GIL` held had
been allowed for historical reason. It is no longer allowed.

- bpo-40826: :c:func:`PyOS_InterruptOccurred` now fails with a fatal error
if it is called with the GIL released.

- bpo-40792: The result of :c:func:`PyNumber_Index` now always has exact
type :class:`int`. Previously, the result could have been an instance of a
subclass of ``int``.

- bpo-39573: Convert :c:func:`Py_REFCNT` and :c:func:`Py_SIZE` macros to
static inline functions. They cannot be used as l-value anymore: use
:c:func:`Py_SET_REFCNT` and :c:func:`Py_SET_SIZE` to set an object
reference count and size. This change is backward incompatible on purpose,
to prepare the C API for an opaque :c:type:`PyObject` structure.

- bpo-40703: The PyType_FromSpec*() functions no longer overwrite the type's
"__module__" attribute if it is set via "Py_tp_members" or "Py_tp_getset".

- bpo-39583: Remove superfluous "extern C" declarations from
``Include/cpython/*.h``.

What's New in Python 3.9.0 beta 1?
==================================

*Release date: 2020-05-19*

Security
--------

- bpo-40501: :mod:`uuid` no longer uses :mod:`ctypes` to load
:file:`libuuid` or :file:`rpcrt4.dll` at runtime.

Core and Builtins
-----------------

- bpo-40663: Correctly generate annotations where parentheses are omitted
but required (e.g: ``Type[(str, int, *other))]``.

- bpo-40596: Fixed :meth:`str.isidentifier` for non-canonicalized strings
containing non-BMP characters on Windows.

- bpo-40593: Improved syntax errors for invalid characters in source code.

- bpo-40585: Fixed a bug when using :func:`codeop.compile_command` that was
causing exceptions to be swallowed with the new parser. Patch by Pablo
Galindo

- bpo-40566: Apply :pep:`573` to :mod:`abc`.

- bpo-40502: Initialize ``n->n_col_offset``. (Patch by Joannah Nanjekye)

- bpo-40527: Fix command line argument parsing: no longer write errors
multiple times into stderr.

- bpo-1635741: Port :mod:`errno` to multiphase initialization (:pep:`489`).

- bpo-40523: Add pass-throughs for :func:`hash` and :func:`reversed` to
:class:`weakref.proxy` objects. Patch by Pablo Galindo.

- bpo-1635741: Port :mod:`syslog` to multiphase initialization (:pep:`489`).

- bpo-40246: Reporting a specialised error message for invalid string
prefixes, which was introduced in :issue:`40246`, is being reverted due to
backwards compatibility concerns for strings that immediately follow a
reserved keyword without whitespace between them. Constructs like
`bg="#d00" if clear else"#fca"` were failing to parse, which is not an
acceptable breakage on such short notice.

- bpo-40417: Fix imp module deprecation warning when PyImport_ReloadModule
is called. Patch by Robert Rouhani.

- bpo-40408: Fixed support of nested type variables in GenericAlias (e.g.
``list[list[T]]``).

- bpo-1635741: Port _stat module to multiphase initialization (:pep:`489`).

- bpo-29587: Enable implicit exception chaining when calling
:meth:`generator.throw`.

- bpo-40328: Add tools for generating mappings headers for CJKCodecs.

- bpo-40228: Setting frame.f_lineno is now robust w.r.t. changes in the
source-to-bytecode compiler

- bpo-38880: Added the ability to list interpreters associated with channel
ends in the internal subinterpreters module.

- bpo-37986: Improve performance of :c:func:`PyLong_FromDouble` for values
that fit into :c:expr:`long`.

Library
-------

- bpo-40662: Fixed :func:`ast.get_source_segment` for ast nodes that have
incomplete location information. Patch by Irit Katriel.

- bpo-40665: Convert :mod:`bisect` to use Argument Clinic.

- bpo-40536: Added the :func:`~zoneinfo.available_timezones` function to the
:mod:`zoneinfo` module. Patch by Paul Ganssle.

- bpo-40645: The :class:`hmac.HMAC` exposes internal implementation details.
The attributes ``digest_cons``, ``inner``, and ``outer`` are deprecated
and will be removed in the future.

- bpo-40645: The internal module ``_hashlib`` wraps and exposes OpenSSL's
HMAC API. The new code will be used in Python 3.10 after the internal
implementation details of the pure Python HMAC module are no longer part
of the public API.

- bpo-40637: Builtin hash modules can now be disabled or selectively enabled
with ``configure --with-builtin-hashlib-hashes=sha3,blake1`` or
``--without-builtin-hashlib-hashes``.

- bpo-37630: The :mod:`hashlib` module can now use SHA3 hashes and SHAKE XOF
from OpenSSL when available.

- bpo-40479: The :mod:`hashlib` now compiles with OpenSSL 3.0.0-alpha2.

- bpo-40257: Revert changes to :func:`inspect.getdoc`.

- bpo-40607: When cancelling a task due to timeout, :meth:`asyncio.wait_for`
will now propagate the exception if an error happens during cancellation.
Patch by Roman Skurikhin.

- bpo-40612: Fix edge cases in SyntaxError formatting. If the offset is <=
0, no caret is printed. If the offset is > line length, the caret is
printed pointing just after the last character.

- bpo-40597: If text content lines are longer than policy.max_line_length,
always use a content-encoding to make sure they are wrapped.

- bpo-40571: Added functools.cache() as a simpler, more discoverable way to
access the unbounded cache variant of lru_cache(maxsize=None).

- bpo-40503: :pep:`615`, the :mod:`zoneinfo` module. Adds support for the
IANA time zone database.

- bpo-40397: Removed attributes ``__args__`` and ``__parameters__`` from
special generic aliases like ``typing.List`` (not subscripted).

- bpo-40549: Convert posixmodule.c ("posix" or "nt" module) to the
multiphase initialization (PEP 489).

- bpo-31033: Add a ``msg`` argument to :meth:`Future.cancel` and
:meth:`Task.cancel`.

- bpo-40541: Added an optional *counts* parameter to random.sample().

- bpo-40515: The :mod:`ssl` and :mod:`hashlib` modules now actively check
that OpenSSL is build with thread support. Python 3.7.0 made thread
support mandatory and no longer works safely with a no-thread builds.

- bpo-31033: When a :class:`asyncio.Task` is cancelled, the exception
traceback now chains all the way back to where the task was first
interrupted.

- bpo-40504: :func:`functools.lru_cache` objects can now be the targets of
weakrefs.

- bpo-40559: Fix possible memory leak in the C implementation of
:class:`asyncio.Task`.

- bpo-40480: ``fnmatch.fnmatch()`` could take exponential time in the
presence of multiple ``*`` pattern characters. This was repaired by
generating more elaborate regular expressions to avoid futile
backtracking.

- bpo-40495: :mod:`compileall` is now able to use hardlinks to prevent
duplicates in a case when ``.pyc`` files for different optimization levels
have the same content.

- bpo-40457: The ssl module now support OpenSSL builds without TLS 1.0 and
1.1 methods.

- bpo-40355: Improve error reporting in :func:`ast.literal_eval` in the
presence of malformed :class:`ast.Dict` nodes instead of silently ignoring
any non-conforming elements. Patch by Curtis Bucher.

- bpo-40465: Deprecated the optional *random* argument to
*random.shuffle()*.

- bpo-40459: :func:`platform.win32_ver` now produces correct *ptype* strings
instead of empty strings.

- bpo-39435: The first argument of :func:`pickle.loads` is now
positional-only.

- bpo-39305: Update :mod:`nntplib` to merge :class:`nntplib.NNTP` and
:class:`nntplib._NNTPBase`. Patch by Dong-hee Na.

- bpo-32494: Update :mod:`dbm.gnu` to use gdbm_count if possible when
calling :func:`len`. Patch by Dong-hee Na.

- bpo-40453: Add ``isolated=True`` keyword-only parameter to
``_xxsubinterpreters.create()``. An isolated subinterpreter cannot spawn
threads, spawn a child process or call ``os.fork()``.

- bpo-40286: Remove ``_random.Random.randbytes()``: the C implementation of
``randbytes()``. Implement the method in Python to ease subclassing:
``randbytes()`` now directly reuses ``getrandbits()``.

- bpo-40394: Added default arguments to
:meth:`difflib.SequenceMatcher.find_longest_match()`.

- bpo-39995: Fix a race condition in concurrent.futures._ThreadWakeup:
access to _ThreadWakeup is now protected with the shutdown lock.

- bpo-30966: ``Process.shutdown(wait=True)`` of :mod:`concurrent.futures`
now closes explicitly the result queue.

- bpo-30966: Add a new :meth:`~multiprocessing.SimpleQueue.close` method to
the :class:`~multiprocessing.SimpleQueue` class to explicitly close the
queue.

- bpo-39966: Revert bpo-25597. :class:`unittest.mock.MagicMock` with wraps'
set uses default return values for magic methods.

- bpo-39791: Added ``files()`` function to importlib.resources with support
for subdirectories in package data, matching backport in
importlib_resources 1.5.

- bpo-40375: :meth:`imaplib.IMAP4.unselect` is added. Patch by Dong-hee Na.

- bpo-40389: ``repr()`` now returns ``typing.Optional[T]`` when called for
``typing.Union`` of two types, one of which is ``NoneType``.

- bpo-40291: Add support for CAN_J1939 sockets (available on Linux 5.4+)

- bpo-40273: :class:`types.MappingProxyType` is now reversible.

- bpo-39075: The repr for :class:`types.SimpleNamespace` is now insertion
ordered rather than alphabetical.

- bpo-40192: On AIX, :func:`~time.thread_time` is now implemented with
``thread_cputime()`` which has nanosecond resolution, rather than
``clock_gettime(CLOCK_THREAD_CPUTIME_ID)`` which has a resolution of 10
milliseconds. Patch by Batuhan Taskaya.

- bpo-40025: Raise TypeError when _generate_next_value_ is defined after
members. Patch by Ethan Onstott.

- bpo-39058: In the argparse module, the repr for Namespace() and other
argument holders now displayed in the order attributes were added.
Formerly, it displayed in alphabetical order even though argument order is
preserved the user visible parts of the module.

- bpo-24416: The ``isocalendar()`` methods of :class:`datetime.date` and
:class:`datetime.datetime` now return a :term:`named tuple` instead of a
:class:`tuple`.

Documentation
-------------

- bpo-34790: Add version of removal for explicit passing of coros to
`asyncio.wait()`'s documentation

- bpo-40561: Provide docstrings for webbrowser open functions.

- bpo-40499: Mention that :func:`asyncio.wait` requires a non-empty set of
awaitables.

- bpo-39705: Tutorial example for sorted() in the Loop Techniques section is
given a better explanation. Also a new example is included to explain
sorted()'s basic behavior.

- bpo-39435: Fix an incorrect signature for :func:`pickle.loads` in the docs

Tests
-----

- bpo-40055: distutils.tests now saves/restores warnings filters to leave
them unchanged. Importing tests imports docutils which imports
pkg_resources which adds a warnings filter.

- bpo-40436: test_gdb and test.pythoninfo now check gdb command exit code.

Build
-----

- bpo-40653: Move _dirnameW out of HAVE_SYMLINK to fix a potential compiling
issue.

- bpo-40514: Add ``--with-experimental-isolated-subinterpreters`` build
option to ``configure``: better isolate subinterpreters, experimental
build mode.

Windows
-------

- bpo-40650: Include winsock2.h in pytime.c for timeval.

- bpo-40458: Increase reserved stack space to prevent overflow crash on
Windows.

- bpo-39148: Add IPv6 support to :mod:`asyncio` datagram endpoints in
ProactorEventLoop. Change the raised exception for unknown address
families to ValueError as it's not coming from Windows API.

macOS
-----

- bpo-34956: When building Python on macOS from source, ``_tkinter`` now
links with non-system Tcl and Tk frameworks if they are installed in
``/Library/Frameworks``, as had been the case on older releases of macOS.
If a macOS SDK is explicitly configured, by using
``--enable-universalsdk=`` or ``-isysroot``, only the SDK itself is
searched. The default behavior can still be overridden with
``--with-tcltk-includes`` and ``--with-tcltk-libs``.

- bpo-35569: Expose RFC 3542 IPv6 socket options.

Tools/Demos
-----------

- bpo-40479: Update multissltest helper to test with latest OpenSSL 1.0.2,
1.1.0, 1.1.1, and 3.0.0-alpha.

- bpo-40431: Fix a syntax typo in ``turtledemo`` that now raises a
``SyntaxError``.

- bpo-40163: Fix multissltest tool. OpenSSL has changed download URL for old
releases. The multissltest tool now tries to download from current and old
download URLs.

C API
-----

- bpo-39465: Remove the ``_PyUnicode_ClearStaticStrings()`` function from
the C API.

- bpo-38787: Add PyCFunction_CheckExact() macro for exact type checks now
that we allow subtypes of PyCFunction, as well as PyCMethod_CheckExact()
and PyCMethod_Check() for the new PyCMethod subtype.

- bpo-40545: Declare ``_PyErr_GetTopmostException()`` with ``PyAPI_FUNC()``
to properly export the function in the C API. The function remains private
(``_Py``) prefix.

- bpo-40412: Nullify inittab_copy during finalization, preventing future
interpreter initializations in an embedded situation from crashing. Patch
by Gregory Szorc.

- bpo-40429: The :c:func:`PyThreadState_GetFrame` function now returns a
strong reference to the frame.

- bpo-40428: Remove the following functions from the C API. Call
:c:func:`PyGC_Collect` explicitly to free all free lists.

* ``PyAsyncGen_ClearFreeLists()``
* ``PyContext_ClearFreeList()``
* ``PyDict_ClearFreeList()``
* ``PyFloat_ClearFreeList()``
* ``PyFrame_ClearFreeList()``
* ``PyList_ClearFreeList()``
* ``PySet_ClearFreeList()``
* ``PyTuple_ClearFreeList()``

- bpo-40421: New :c:func:`PyFrame_GetBack` function: get the frame next
outer frame.

- bpo-40421: New :c:func:`PyFrame_GetCode` function: return a borrowed
reference to the frame code.

- bpo-40217: Ensure that instances of types created with
:c:func:`PyType_FromSpecWithBases` will visit its class object when
traversing references in the garbage collector (implemented as an
extension of the provided :c:member:`~PyTypeObject.tp_traverse`). Patch by
Pablo Galindo.

- bpo-38787: Module C state is now accessible from C-defined heap type
methods (:pep:`573`). Patch by Marcel Plch and Petr Viktorin.

What's New in Python 3.9.0 alpha 6?
===================================

*Release date: 2020-04-27*

Security
--------

- bpo-40121: Fixes audit events raised on creating a new socket.

- bpo-39073: Disallow CR or LF in email.headerregistry.Address arguments to
guard against header injection attacks.

- bpo-39503: CVE-2020-8492: The
:class:`~urllib.request.AbstractBasicAuthHandler` class of the
:mod:`urllib.request` module uses an inefficient regular expression which
can be exploited by an attacker to cause a denial of service. Fix the
regex to prevent the catastrophic backtracking. Vulnerability reported by
Ben Caller and Matt Schwager.

Core and Builtins
-----------------

- bpo-40313: Improve the performance of bytes.hex().

- bpo-40334: Switch to a new parser, based on PEG. For more details see PEP
617. To temporarily switch back to the old parser, use ``-X oldparser`` or
``PYTHONOLDPARSER=1``. In Python 3.10 we will remove the old parser
completely, including the ``parser`` module (already deprecated) and
anything that depends on it.

- bpo-40267: Fix the tokenizer to display the correct error message, when
there is a SyntaxError on the last input character and no newline follows.
It used to be `unexpected EOF while parsing`, while it should be `invalid
syntax`.

- bpo-39522: Correctly unparse explicit ``u`` prefix for strings when
postponed evaluation for annotations activated. Patch by Batuhan Taskaya.

- bpo-40246: Report a specialized error message, `invalid string prefix`,
when the tokenizer encounters a string with an invalid prefix.

- bpo-40082: Fix the signal handler: it now always uses the main
interpreter, rather than trying to get the current Python thread state.

- bpo-37388: str.encode() and str.decode() no longer check the encoding and
errors in development mode or in debug mode during Python finalization.
The codecs machinery can no longer work on very late calls to str.encode()
and str.decode().

- bpo-40077: Fix possible refleaks in :mod:`_json`, memo of PyScannerObject
should be traversed.

- bpo-37207: Speed up calls to ``dict()`` by using the :pep:`590`
``vectorcall`` calling convention.

- bpo-40141: Add column and line information to ``ast.keyword`` nodes. Patch
by Pablo Galindo.

- bpo-1635741: Port :mod:`resource` to multiphase initialization
(:pep:`489`).

- bpo-1635741: Port :mod:`math` to multiphase initialization (:pep:`489`).

- bpo-1635741: Port _uuid module to multiphase initialization (:pep:`489`).

- bpo-40077: Convert json module to use :c:func:`PyType_FromSpec`.

- bpo-40067: Improve the error message for multiple star expressions in an
assignment. Patch by Furkan Onder

- bpo-1635741: Port _functools module to multiphase initialization (PEP
489). Patch by Paulo Henrique Silva.

- bpo-1635741: Port operator module to multiphase initialization (PEP 489).
Patch by Paulo Henrique Silva.

- bpo-20526: Fix :c:func:`PyThreadState_Clear()`. ``PyThreadState.frame`` is
a borrowed reference, not a strong reference: ``PyThreadState_Clear()``
must not call ``Py_CLEAR(tstate->frame)``.

- bpo-1635741: Port time module to multiphase initialization (:pep:`489`).
Patch by Paulo Henrique Silva.

- bpo-1635741: Port _weakref extension module to multiphase initialization
(:pep:`489`).

- bpo-40020: Fix a leak and subsequent crash in parsetok.c caused by realloc
misuse on a rare codepath.

- bpo-39939: Added str.removeprefix and str.removesuffix methods and
corresponding bytes, bytearray, and collections.UserString methods to
remove affixes from a string if present. See :pep:`616` for a full
description. Patch by Dennis Sweeney.

- bpo-39481: Implement PEP 585. This supports list[int], tuple[str, ...]
etc.

- bpo-32894: Support unparsing of infinity numbers in postponed annotations.
Patch by Batuhan Taşkaya.

- bpo-37207: Speed up calls to ``list()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Mark Shannon.

Library
-------

- bpo-40398: :func:`typing.get_args` now always returns an empty tuple for
special generic aliases.

- bpo-40396: Functions :func:`typing.get_origin`, :func:`typing.get_args`
and :func:`typing.get_type_hints` support now generic aliases like
``list[int]``.

- bpo-38061: Optimize the :mod:`subprocess` module on FreeBSD using
``closefrom()``. A single ``close(fd)`` syscall is cheap, but when
``sysconf(_SC_OPEN_MAX)`` is high, the loop calling ``close(fd)`` on each
file descriptor can take several milliseconds.

The workaround on FreeBSD to improve performance was to load and mount the
fdescfs kernel module, but this is not enabled by default.

Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans
(kevans) and Kubilay Kocak (koobs):
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274

- bpo-38061: On FreeBSD, ``os.closerange(fd_low, fd_high)`` now calls
``closefrom(fd_low)`` if *fd_high* is greater than or equal to
``sysconf(_SC_OPEN_MAX)``.

Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans
(kevans) and Kubilay Kocak (koobs):
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274

- bpo-40360: The :mod:`lib2to3` module is pending deprecation due to
:pep:`617`.

- bpo-40138: Fix the Windows implementation of :func:`os.waitpid` for exit
code larger than ``INT_MAX >> 8``. The exit status is now interpreted as
an unsigned number.

- bpo-39942: Set "__main__" as the default module name when "__name__" is
missing in :class:`typing.TypeVar`. Patch by Weipeng Hong.

- bpo-40275: The :mod:`logging` package is now imported lazily in
:mod:`unittest` only when the :meth:`~unittest.TestCase.assertLogs`
assertion is used.

- bpo-40275: The :mod:`asyncio` package is now imported lazily in
:mod:`unittest` only when the :class:`~unittest.IsolatedAsyncioTestCase`
class is used.

- bpo-40330: In :meth:`ShareableList.__setitem__`, check the size of a new
string item after encoding it to utf-8, not before.

- bpo-40148: Added :meth:`pathlib.Path.with_stem()` to create a new Path
with the stem replaced.

- bpo-40325: Deprecated support for set objects in random.sample().

- bpo-40257: Improved help for the :mod:`typing` module. Docstrings are now
shown for all special forms and special generic aliases (like ``Union``
and ``List``). Using ``help()`` with generic alias like ``List[int]`` will
show the help for the correspondent concrete type (``list`` in this case).

- bpo-40257: func:`inspect.getdoc` no longer returns docstring inherited
from the type of the object or from parent class if it is a class if it is
not defined in the object itself. In :mod:`pydoc` the documentation string
is now shown not only for class, function, method etc, but for any object
that has its own ``__doc__`` attribute.

- bpo-40287: Fixed ``SpooledTemporaryFile.seek()`` to return the position.

- bpo-40290: Added zscore() to statistics.NormalDist().

- bpo-40282: Allow ``random.getrandbits(0)`` to succeed and to return 0.

- bpo-40286: Add :func:`random.randbytes` function and
:meth:`random.Random.randbytes` method to generate random bytes.

- bpo-40277: :func:`collections.namedtuple` now provides a human-readable
repr for its field accessors.

- bpo-40270: The included copy of sqlite3 on Windows is now compiled with
the json extension. This allows the use of functions such as
``json_object``.

- bpo-29255: Wait in `KqueueSelector.select` when no fds are registered

- bpo-40260: Ensure :mod:`modulefinder` uses :func:`io.open_code` and
respects coding comments.

- bpo-40234: Allow again to spawn daemon threads in subinterpreters (revert
change which denied them).

- bpo-39207: Workers in :class:`~concurrent.futures.ProcessPoolExecutor` are
now spawned on demand, only when there are no available idle workers to
reuse. This optimizes startup overhead and reduces the amount of lost CPU
time to idle workers. Patch by Kyle Stanley.

- bpo-40091: Fix a hang at fork in the logging module: the new private
_at_fork_reinit() method is now used to reinitialize locks at fork in the
child process.

- bpo-40149: Implement traverse and clear slots in _abc._abc_data type.

- bpo-40208: Remove deprecated :meth:`symtable.SymbolTable.has_exec`.

- bpo-40196: Fix a bug in the :mod:`symtable` module that was causing
incorrectly report global variables as local. Patch by Pablo Galindo.

- bpo-40190: Add support for ``_SC_AIX_REALMEM`` to :func:`posix.sysconf`.

- bpo-40182: Removed the ``_field_types`` attribute of the
:class:`typing.NamedTuple` class.

- bpo-36517: Multiple inheritance with :class:`typing.NamedTuple` now raises
an error instead of silently ignoring other types.

- bpo-40126: Fixed reverting multiple patches in unittest.mock. Patcher's
``__exit__()`` is now never called if its ``__enter__()`` is failed.
Returning true from ``__exit__()`` silences now the exception.

- bpo-40094: CGIHTTPRequestHandler of http.server now logs the CGI script
exit code, rather than the CGI script exit status of os.waitpid(). For
example, if the script is killed by signal 11, it now logs: "CGI script
exit code -11."

- bpo-40108: Improve the error message when triying to import a module using
:mod:`runpy` and incorrently use the ".py" extension at the end of the
module name. Patch by Pablo Galindo.

- bpo-40094: Add :func:`os.waitstatus_to_exitcode` function: convert a wait
status to an exit code.

- bpo-40089: Fix threading._after_fork(): if fork was not called by a thread
spawned by threading.Thread, threading._after_fork() now creates a
_MainThread instance for _main_thread, instead of a _DummyThread instance.

- bpo-40089: Add a private ``_at_fork_reinit()`` method to
:class:`_thread.Lock`, :class:`_thread.RLock`, :class:`threading.RLock`
and :class:`threading.Condition` classes: reinitialize the lock at fork in
the child process, reset the lock to the unlocked state. Rename also the
private ``_reset_internal_locks()`` method of :class:`threading.Event` to
``_at_fork_reinit()``.

- bpo-25780: Expose :data:`~socket.CAN_RAW_JOIN_FILTERS` in the
:mod:`socket` module.

- bpo-39503: :class:`~urllib.request.AbstractBasicAuthHandler` of
:mod:`urllib.request` now parses all WWW-Authenticate HTTP headers and
accepts multiple challenges per header: use the realm of the first Basic
challenge.

- bpo-39812: Removed daemon threads from :mod:`concurrent.futures` by adding
an internal `threading._register_atexit()`, which calls registered
functions prior to joining all non-daemon threads. This allows for
compatibility with subinterpreters, which don't support daemon threads.

- bpo-40050: Fix ``importlib._bootstrap_external``: avoid creating a new
``winreg`` builtin module if it's already available in
:data:`sys.modules`, and remove redundant imports.

- bpo-40014: Fix ``os.getgrouplist()``: if ``getgrouplist()`` function fails
because the group list is too small, retry with a larger group list. On
failure, the glibc implementation of ``getgrouplist()`` sets ``ngroups``
to the total number of groups. For other implementations, double the group
list size.

- bpo-40017: Add :data:`time.CLOCK_TAI` constant if the operating system
support it.

- bpo-40016: In re docstring, clarify the relationship between inline and
argument compile flags.

- bpo-39953: Update internal table of OpenSSL error codes in the ``ssl``
module.

- bpo-36144: Added :pep:`584` operators to
:class:`weakref.WeakValueDictionary`.

- bpo-36144: Added :pep:`584` operators to
:class:`weakref.WeakKeyDictionary`.

- bpo-38891: Fix linear runtime behaviour of the `__getitem__` and
`__setitem__` methods in
:class:`multiprocessing.shared_memory.ShareableList`. This avoids
quadratic performance when iterating a `ShareableList`. Patch by Thomas
Krennwallner.

- bpo-39682: Remove undocumented support for *closing* a `pathlib.Path`
object via its context manager. The context manager magic methods remain,
but they are now a no-op, making `Path` objects immutable.

- bpo-36144: Added :pep:`584` operators (``|`` and ``|=``) to
:class:`collections.ChainMap`.

- bpo-39011: Normalization of line endings in ElementTree attributes was
removed, as line endings which were replaced by entity numbers should be
preserved in original form.

- bpo-38410: Properly handle :func:`sys.audit` failures in
:func:`sys.set_asyncgen_hooks`.

- bpo-36541: lib2to3 now recognizes named assignment expressions (the walrus
operator, ``:=``)

- bpo-35967: In platform, delay the invocation of 'uname -p' until the
processor attribute is requested.

- bpo-35113: :meth:`inspect.getsource` now returns correct source code for
inner class with same name as module level class. Decorators are also
returned as part of source of the class. Patch by Karthikeyan
Singaravelan.

- bpo-33262: Deprecate passing None as an argument for
:func:`shlex.split()`'s ``s`` parameter. Patch by Zackery Spytz.

- bpo-31758: Prevent crashes when using an uninitialized
``_elementtree.XMLParser`` object. Patch by Oren Milman.

Documentation
-------------

- bpo-27635: The pickle documentation incorrectly claimed that ``__new__``
isn't called by default when unpickling.

- bpo-39879: Updated :ref:`datamodel` docs to include :func:`dict` insertion
order preservation. Patch by Furkan Onder and Samy Lahfa.

- bpo-38387: Document :c:macro:`PyDoc_STRVAR` macro in the C-API reference.

- bpo-13743: Some methods within xml.dom.minidom.Element class are now
better documented.

Tests
-----

- bpo-31904: Set expected default encoding in test_c_locale_coercion.py for
VxWorks RTOS.

- bpo-40162: Update Travis CI configuration to OpenSSL 1.1.1f.

- bpo-40146: Update OpenSSL to 1.1.1f in Azure Pipelines.

- bpo-40094: Add :func:`test.support.wait_process` function.

- bpo-40003: ``test.bisect_cmd`` now copies Python command line options like
``-O`` or ``-W``. Moreover, emit a warning if ``test.bisect_cmd`` is used
with ``-w``/``--verbose2`` option.

- bpo-39380: Add the encoding in :class:`ftplib.FTP` and
:class:`ftplib.FTP_TLS` to the constructor as keyword-only and change the
default from ``latin-1`` to ``utf-8`` to follow :rfc:`2640`.

- bpo-39793: Use the same domain when testing ``make_msgid``. Patch by
Batuhan Taskaya.

- bpo-1812: Fix newline handling in doctest.testfile when loading from a
package whose loader has a get_data method. Patch by Peter Donis.

Build
-----

- bpo-38360: Support single-argument form of macOS -isysroot flag.

- bpo-40158: Fix CPython MSBuild Properties in NuGet Package
(build/native/python.props)

- bpo-38527: Fix configure check on Solaris for "float word ordering":
sometimes, the correct "grep" command was not being used. Patch by Arnon
Yaari.

Windows
-------

- bpo-40164: Updates Windows to OpenSSL 1.1.1f

- bpo-8901: Ignore the Windows registry when the ``-E`` option is used.

macOS
-----

- bpo-38329: python.org macOS installers now update the Current version
symlink of /Library/Frameworks/Python.framework/Versions for 3.9 installs.
Previously, Current was only updated for Python 2.x installs. This should
make it easier to embed Python 3 into other macOS applications.

- bpo-40164: Update macOS installer builds to use OpenSSL 1.1.1g.

IDLE
----

- bpo-38439: Add a 256×256 pixel IDLE icon to support more modern
environments. Created by Andrew Clover. Delete the unused macOS idle.icns
icon file.

- bpo-38689: IDLE will no longer freeze when inspect.signature fails when
fetching a calltip.

Tools/Demos
-----------

- bpo-40385: Removed the checkpyc.py tool. Please see compileall without
force mode as a potential alternative.

- bpo-40179: Fixed translation of ``#elif`` in Argument Clinic.

- bpo-40094: Fix ``which.py`` script exit code: it now uses
:func:`os.waitstatus_to_exitcode` to convert :func:`os.system` exit status
into an exit code.

C API
-----

- bpo-40241: Move the :c:type:`PyGC_Head` structure to the internal C API.

- bpo-40170: Convert :c:func:`PyObject_IS_GC` macro to a function to hide
implementation details.

- bpo-40241: Add the functions :c:func:`PyObject_GC_IsTracked` and
:c:func:`PyObject_GC_IsFinalized` to the public API to allow to query if
Python objects are being currently tracked or have been already finalized
by the garbage collector respectively. Patch by Pablo Galindo.

- bpo-40170: The :c:func:`PyObject_NEW` macro becomes an alias to the
:c:func:`PyObject_New` macro, and the :c:func:`PyObject_NEW_VAR` macro
becomes an alias to the :c:func:`PyObject_NewVar` macro, to hide
implementation details. They no longer access directly the
:c:member:`PyTypeObject.tp_basicsize` member.

- bpo-40170: :c:func:`PyType_HasFeature` now always calls
:c:func:`PyType_GetFlags` to hide implementation details. Previously, it
accessed directly the :c:member:`PyTypeObject.tp_flags` member when the
limited C API was not used.

- bpo-40170: Convert the :c:func:`PyObject_GET_WEAKREFS_LISTPTR` macro to a
function to hide implementation details: the macro accessed directly to
the :c:member:`PyTypeObject.tp_weaklistoffset` member.

- bpo-40170: Convert :c:func:`PyObject_CheckBuffer` macro to a function to
hide implementation details: the macro accessed directly the
:c:member:`PyTypeObject.tp_as_buffer` member.

- bpo-40170: Always declare :c:func:`PyIndex_Check` as an opaque function to
hide implementation details: remove ``PyIndex_Check()`` macro. The macro
accessed directly the :c:member:`PyTypeObject.tp_as_number` member.

- bpo-39947: Add :c:func:`PyThreadState_GetID` function: get the unique
identifier of a Python thread state.

What's New in Python 3.9.0 alpha 5?
===================================

*Release date: 2020-03-23*

Security
--------

- bpo-38576: Disallow control characters in hostnames in http.client,
addressing CVE-2019-18348. Such potentially malicious header injection
URLs now cause a InvalidURL to be raised.

Core and Builtins
-----------------

- bpo-40010: Optimize pending calls in multithreaded applications. If a
thread different than the main thread schedules a pending call
(:c:func:`Py_AddPendingCall`), the bytecode evaluation loop is no longer
interrupted at each bytecode instruction to check for pending calls which
cannot be executed. Only the main thread can execute pending calls.

Previously, the bytecode evaluation loop was interrupted at each
instruction until the main thread executes pending calls.

- bpo-1635741: Port _weakref extension module to multiphase initialization
(:pep:`489`).

- bpo-1635741: Port _collections module to multiphase initialization
(:pep:`489`).

- bpo-40010: Optimize signal handling in multithreaded applications. If a
thread different than the main thread gets a signal, the bytecode
evaluation loop is no longer interrupted at each bytecode instruction to
check for pending signals which cannot be handled. Only the main thread of
the main interpreter can handle signals.

Previously, the bytecode evaluation loop was interrupted at each
instruction until the main thread handles signals.

- bpo-39984: If :c:func:`Py_AddPendingCall` is called in a subinterpreter,
the function is now scheduled to be called from the subinterpreter, rather
than being called from the main interpreter. Each subinterpreter now has
its own list of scheduled calls.

- bpo-1635741: Port _heapq module to multiphase initialization.

- bpo-1635741: Port itertools module to multiphase initialization
(:pep:`489`).

- bpo-37207: Speed up calls to ``frozenset()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-39984: subinterpreters: Move
``_PyRuntimeState.ceval.tracing_possible`` to
``PyInterpreterState.ceval.tracing_possible``: each interpreter now has
its own variable.

- bpo-37207: Speed up calls to ``set()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-1635741: Port _statistics module to multiphase initialization
(:pep:`489`).

- bpo-39968: Use inline function to replace extension modules'
get_module_state macros.

- bpo-39965: Correctly raise ``SyntaxError`` if *await* is used inside
non-async functions and ``PyCF_ALLOW_TOP_LEVEL_AWAIT`` is set (like in the
asyncio REPL). Patch by Pablo Galindo.

- bpo-39562: Allow executing asynchronous comprehensions on the top level
when the ``PyCF_ALLOW_TOP_LEVEL_AWAIT`` flag is given. Patch by Batuhan
Taskaya.

- bpo-37207: Speed up calls to ``tuple()`` by using the :pep:`590`
``vectorcall`` calling convention. Patch by Dong-hee Na.

- bpo-38373: Changed list overallocation strategy. It no longer
overallocates if the new size is closer to overallocated size than to the
old size and adds padding.

- bpo-39926: Update Unicode database to Unicode version 13.0.0.

- bpo-19466: Clear the frames of daemon threads earlier during the Python
shutdown to call objects destructors. So "unclosed file" resource warnings
are now emitted for daemon threads in a more reliable way.

- bpo-38894: Fix a bug that was causing incomplete results when calling
``pathlib.Path.glob`` in the presence of symlinks that point to files
where the user does not have read access. Patch by Pablo Galindo and Matt
Wozniski.

- bpo-39877: Fix :c:func:`PyEval_RestoreThread` random crash at exit with
daemon threads. It now accesses the ``_PyRuntime`` variable directly
instead of using ``tstate->interp->runtime``, since ``tstate`` can be a
dangling pointer after :c:func:`Py_Finalize` has been called. Moreover,
the daemon thread now exits before trying to take the GIL.

- bpo-39871: Fix a possible :exc:`SystemError` in
``math.{atan2,copysign,remainder}()`` when the first argument cannot be
converted to a :class:`float`. Patch by Zackery Spytz.

- bpo-39776: Fix race condition where threads created by PyGILState_Ensure()
could get a duplicate id.

This affects consumers of tstate->id like the contextvar caching
machinery, which could return invalid cached objects under heavy thread
load (observed in embedded scenarios).

- bpo-39778: Fixed a crash due to incorrect handling of weak references in
``collections.OrderedDict`` classes. Patch by Pablo Galindo.

- bpo-1635741: Port audioop extension module to multiphase initialization
(:pep:`489`).

- bpo-39702: Relax :term:`decorator` grammar restrictions to allow any valid
expression (:pep:`614`).

- bpo-38091: Tweak import deadlock detection code to not deadlock itself.

- bpo-1635741: Port _locale extension module to multiphase initialization
(:pep:`489`).

- bpo-39087: Optimize :c:func:`PyUnicode_AsUTF8` and
:c:func:`PyUnicode_AsUTF8AndSize` slightly when they need to create
internal UTF-8 cache.

- bpo-39520: Fix unparsing of ext slices with no items (``foo[:,]``). Patch
by Batuhan Taskaya.

- bpo-39220: Do not optimize annotations if 'from __future__ import
annotations' is used. Patch by Pablo Galindo.

- bpo-35712: Using :data:`NotImplemented` in a boolean context has been
deprecated. Patch contributed by Josh Rosenberg.

- bpo-22490: Don't leak environment variable ``__PYVENV_LAUNCHER__`` into
the interpreter session on macOS.

Library
-------

- bpo-39830: Add :class:`zipfile.Path` to ``__all__`` in the :mod:`zipfile`
module.

- bpo-40000: Improved error messages for validation of ``ast.Constant``
nodes. Patch by Batuhan Taskaya.

- bpo-39999: ``__module__`` of the AST node classes is now set to "ast"
instead of "_ast". Added docstrings for dummy AST node classes and
deprecated attributes.

- bpo-39991: :func:`uuid.getnode` now skips IPv6 addresses with the same
string length than a MAC address (17 characters): only use MAC addresses.

- bpo-39988: Deprecated ``ast.AugLoad`` and ``ast.AugStore`` node classes
because they are no longer used.

- bpo-39656: Ensure ``bin/python3.#`` is always present in virtual
environments on POSIX platforms - by Anthony Sottile.

- bpo-39969: Deprecated ``ast.Param`` node class because it's no longer
used. Patch by Batuhan Taskaya.

- bpo-39360: Ensure all workers exit when finalizing a
:class:`multiprocessing.Pool` implicitly via the module finalization
handlers of multiprocessing. This fixes a deadlock situation that can be
experienced when the Pool is not properly finalized via the context
manager or a call to ``multiprocessing.Pool.terminate``. Patch by Batuhan
Taskaya and Pablo Galindo.

- bpo-35370: sys.settrace(), sys.setprofile() and _lsprof.Profiler.enable()
now properly report :c:func:`PySys_Audit` error if "sys.setprofile" or
"sys.settrace" audit event is denied.

- bpo-39936: AIX: Fix _aix_support module when the subprocess is not
available, when building Python from scratch. It now uses new private
_bootsubprocess module, rather than having two implementations depending
if subprocess is available or not. So _aix_support.aix_platform() result
is now the same if subprocess is available or not.

- bpo-36144: :class:`collections.OrderedDict` now implements ``|`` and
``|=`` (:pep:`584`).

- bpo-39652: The column name found in ``sqlite3.Cursor.description`` is now
truncated on the first '[' only if the PARSE_COLNAMES option is set.

- bpo-39915: Ensure :attr:`unittest.mock.AsyncMock.await_args_list` has call
objects in the order of awaited arguments instead of using
:attr:`unittest.mock.Mock.call_args` which has the last value of the call.
Patch by Karthikeyan Singaravelan.

- bpo-36144: Updated :data:`os.environ` and :data:`os.environb` to support
:pep:`584`'s merge (``|``) and update (``|=``) operators.

- bpo-38662: The ``ensurepip`` module now invokes ``pip`` via the ``runpy``
module. Hence it is no longer tightly coupled with the internal API of the
bundled ``pip`` version, allowing easier updates to a newer ``pip``
version both internally and for distributors.

- bpo-38075: Fix the :meth:`random.Random.seed` method when a :class:`bool`
is passed as the seed.

- bpo-39916: More reliable use of ``os.scandir()`` in ``Path.glob()``. It no
longer emits a ResourceWarning when interrupted.

- bpo-39850: :mod:`multiprocessing` now supports abstract socket addresses
(if abstract sockets are supported in the running platform). When creating
arbitrary addresses (like when default-constructing
:class:`multiprocessing.connection.Listener` objects) abstract sockets are
preferred to avoid the case when the temporary-file-generated address is
too large for an AF_UNIX socket address. Patch by Pablo Galindo.

- bpo-36287: :func:`ast.dump()` no longer outputs optional fields and
attributes with default values. The default values for optional fields and
attributes of AST nodes are now set as class attributes (e.g.
``Constant.kind`` is set to ``None``).

- bpo-39889: Fixed :func:`ast.unparse` for extended slices containing a
single element (e.g. ``a[i:j,]``). Remove redundant tuples when index with
a tuple (e.g. ``a[i, j]``).

- bpo-39828: Fix :mod:`json.tool` to catch :exc:`BrokenPipeError`. Patch by
Dong-hee Na.

- bpo-13487: Avoid a possible *"RuntimeError: dictionary changed size during
iteration"* from :func:`inspect.getmodule` when it tried to loop through
:attr:`sys.modules`.

- bpo-39674: Revert "bpo-37330: open() no longer accept 'U' in file mode".
The "U" mode of open() is kept in Python 3.9 to ease transition from
Python 2.7, but will be removed in Python 3.10.

- bpo-28577: The hosts method on 32-bit prefix length IPv4Networks and
128-bit prefix IPv6Networks now returns a list containing the single
Address instead of an empty list.

- bpo-39826: Add getConnection method to logging HTTPHandler to enable
custom connections.

- bpo-39763: Reimplement :func:`distutils.spawn.spawn` function with the
:mod:`subprocess` module.

- bpo-39794: Add --without-decimal-contextvar build option. This enables a
thread-local rather than a coroutine local context.

- bpo-36144: :class:`collections.defaultdict` now implements ``|``
(:pep:`584`).

- bpo-39517: Fix runpy.run_path() when using pathlike objects

- bpo-39775: Change ``inspect.Signature.parameters`` back to
``collections.OrderedDict``. This was changed to ``dict`` in Python
3.9.0a4.

- bpo-39678: Refactor queue_manager in
:class:`concurrent.futures.ProcessPoolExecutor` to make it easier to
maintain.

- bpo-39764: Fix AttributeError when calling get_stack on a PyAsyncGenObject
Task

- bpo-39769: The :func:`compileall.compile_dir` function's *ddir* parameter
and the compileall command line flag `-d` no longer write the wrong
pathname to the generated pyc file for submodules beneath the root of the
directory tree being compiled. This fixes a regression introduced with
Python 3.5.

- bpo-36144: :class:`types.MappingProxyType` objects now support the merge
(``|``) operator from :pep:`584`.

- bpo-38691: The :mod:`importlib` module now ignores the
:envvar:`PYTHONCASEOK` environment variable when the :option:`-E` or
:option:`-I` command line options are being used.

- bpo-39719: Remove :meth:`tempfile.SpooledTemporaryFile.softspace` as files
no longer have the ``softspace`` attribute in Python 3. Patch by Shantanu.

- bpo-39667: Improve pathlib.Path compatibility on zipfile.Path and correct
performance degradation as found in zipp 3.0.

- bpo-39638: Keep ASDL signatures in the docstrings for ``AST`` nodes. Patch
by Batuhan Taskaya

- bpo-39639: Deprecated ``ast.Suite`` node class because it's no longer
used. Patch by Batuhan Taskaya.

- bpo-39609: Add thread_name_prefix to default asyncio executor

- bpo-39548: Fix handling of header in
:class:`urllib.request.AbstractDigestAuthHandler` when the optional
``qop`` parameter is not present.

- bpo-39509: HTTP status codes ``103 EARLY_HINTS`` and ``425 TOO_EARLY`` are
added to :class:`http.HTTPStatus`. Patch by Dong-hee Na.

- bpo-39507: Adding HTTP status 418 "I'm a Teapot" to HTTPStatus in http
library. Patch by Ross Rhodes.

- bpo-39495: Remove default value from *attrs* parameter of
:meth:`xml.etree.ElementTree.TreeBuilder.start` for consistency between
Python and C implementations.

- bpo-38971: Open issue in the BPO indicated a desire to make the
implementation of codecs.open() at parity with io.open(), which implements
a try/except to assure file stream gets closed before an exception is
raised.

- bpo-38641: Added starred expressions support to ``return`` and ``yield``
statements for ``lib2to3``. Patch by Vlad Emelianov.

- bpo-37534: When using minidom module to generate XML documents the ability
to add Standalone Document Declaration is added. All the changes are made
to generate a document in compliance with Extensible Markup Language (XML)
1.0 (Fifth Edition) W3C Recommendation (available here:
https://www.w3.org/TR/xml/#sec-prolog-dtd).

- bpo-34788: Add support for scoped IPv6 addresses to :mod:`ipaddress`.
Patch by Oleksandr Pavliuk.

- bpo-34822: Simplified AST for subscription. Simple indices are now
represented by their value, extended slices are represented as tuples.
:mod:`ast` classes ``Index`` and ``ExtSlice`` are considered deprecated
and will be removed in future Python versions. In the meantime,
``Index(value)`` now returns a ``value`` itself, ``ExtSlice(slices)``
returns ``Tuple(slices, Load())``.

Documentation
-------------

- bpo-39868: Updated the Language Reference for :pep:`572`.

- bpo-13790: Change 'string' to 'specification' in format doc.

- bpo-17422: The language reference no longer restricts default class
namespaces to dicts only.

- bpo-39530: Fix misleading documentation about mixed-type numeric
comparisons.

- bpo-39718: Update :mod:`token` documentation to reflect additions in
Python 3.8

- bpo-39677: Changed operand name of **MAKE_FUNCTION** from *argc* to
*flags* for module :mod:`dis`

Tests
-----

- bpo-40019: test_gdb now skips tests if it detects that gdb failed to read
debug information because the Python binary is optimized.

- bpo-27807: ``test_site.test_startup_imports()`` is now skipped if a path
of :data:`sys.path` contains a ``.pth`` file.

- bpo-26067: Do not fail test_shutil test_chown test when uid or gid of user
cannot be resolved to a name.

- bpo-39855: test_subprocess.test_user() now skips the test on an user name
if the user name doesn't exist. For example, skip the test if the user
"nobody" doesn't exist on Linux.

Build
-----

- bpo-39761: Fix build with DTrace but without additional DFLAGS.

- bpo-39763: setup.py now uses a basic implementation of the
:mod:`subprocess` module if the :mod:`subprocess` module is not available:
before required C extension modules are built.

- bpo-1294959: Add ``--with-platlibdir`` option to the configure script:
name of the platform-specific library directory, stored in the new
:attr:`sys.platlibdir` attribute. It is used to build the path of
platform-specific extension modules and the path of the standard library.
It is equal to ``"lib"`` on most platforms. On Fedora and SuSE, it is
equal to ``"lib64"`` on 64-bit platforms. Patch by Jan Matějek, Matěj
Cepl, Charalampos Stratakis and Victor Stinner.

Windows
-------

- bpo-39930: Ensures the required :file:`vcruntime140.dll` is included in
install packages.

- bpo-39847: Avoid hang when computer is hibernated whilst waiting for a
mutex (for lock-related objects from :mod:`threading`) around 49-day
uptime.

- bpo-38597: :mod:`distutils` will no longer statically link
:file:`vcruntime140.dll` when a redistributable version is unavailable.
All future releases of CPython will include a copy of this DLL to ensure
distributed extensions can continue to load.

- bpo-38380: Update Windows builds to use SQLite 3.31.1

- bpo-39789: Update Windows release build machines to Visual Studio 2019
(MSVC 14.2).

- bpo-34803: Package for nuget.org now includes repository reference and
bundled icon image.

macOS
-----

- bpo-38380: Update macOS builds to use SQLite 3.31.1

IDLE
----

- bpo-27115: For 'Go to Line', use a Query box subclass with IDLE standard
behavior and improved error checking.

- bpo-39885: Since clicking to get an IDLE context menu moves the cursor,
any text selection should be and now is cleared.

- bpo-39852: Edit "Go to line" now clears any selection, preventing
accidental deletion. It also updates Ln and Col on the status bar.

- bpo-39781: Selecting code context lines no longer causes a jump.

Tools/Demos
-----------

- bpo-36184: Port python-gdb.py to FreeBSD. python-gdb.py now checks for
"take_gil" function name to check if a frame tries to acquire the GIL,
instead of checking for "pthread_cond_timedwait" which is specific to
Linux and can be a different condition than the GIL.

- bpo-38080: Added support to fix ``getproxies`` in the
:mod:`lib2to3.fixes.fix_urllib` module. Patch by José Roberto Meza
Cabrera.

C API
-----

- bpo-40024: Add :c:func:`PyModule_AddType` helper function: add a type to a
module. Patch by Dong-hee Na.

- bpo-39946: Remove ``_PyRuntime.getframe`` hook and remove
``_PyThreadState_GetFrame`` macro which was an alias to
``_PyRuntime.getframe``. They were only exposed by the internal C API.
Remove also ``PyThreadFrameGetter`` type.

- bpo-39947: Add :c:func:`PyThreadState_GetFrame` function: get the current
frame of a Python thread state.

- bpo-37207: Add _PyArg_NoKwnames helper function. Patch by Dong-hee Na.

- bpo-39947: Add :c:func:`PyThreadState_GetInterpreter`: get the interpreter
of a Python thread state.

- bpo-39947: Add :c:func:`PyInterpreterState_Get` function to the limited C
API.

- bpo-35370: If :c:func:`PySys_Audit` fails in :c:func:`PyEval_SetProfile`
or :c:func:`PyEval_SetTrace`, log the error as an unraisable exception.

- bpo-39947: Move the static inline function flavor of
Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() to the internal C API:
they access PyThreadState attributes. The limited C API provides regular
functions which hide implementation details.

- bpo-39947: Py_TRASHCAN_BEGIN_CONDITION and Py_TRASHCAN_END macro no longer
access PyThreadState attributes, but call new private _PyTrash_begin() and
_PyTrash_end() functions which hide implementation details.

- bpo-39884: :c:func:`PyDescr_NewMethod` and :c:func:`PyCFunction_NewEx` now
include the method name in the SystemError "bad call flags" error message
to ease debug.

- bpo-39877: Deprecated :c:func:`PyEval_InitThreads` and
:c:func:`PyEval_ThreadsInitialized`. Calling :c:func:`PyEval_InitThreads`
now does nothing.

- bpo-38249: :c:macro:`Py_UNREACHABLE` is now implemented with
``__builtin_unreachable()`` and analogs in release mode.

- bpo-38643: :c:func:`PyNumber_ToBase` now raises a :exc:`SystemError`
instead of crashing when called with invalid base.

- bpo-39882: The :c:func:`Py_FatalError` function is replaced with a macro
which logs automatically the name of the current function, unless the
``Py_LIMITED_API`` macro is defined.

- bpo-39824: Extension modules: :c:member:`~PyModuleDef.m_traverse`,
:c:member:`~PyModuleDef.m_clear` and :c:member:`~PyModuleDef.m_free`
functions of :c:type:`PyModuleDef` are no longer called if the module
state was requested but is not allocated yet. This is the case immediately
after the module is created and before the module is executed
(:c:data:`Py_mod_exec` function). More precisely, these functions are not
called if :c:member:`~PyModuleDef.m_size` is greater than 0 and the module
state (as returned by :c:func:`PyModule_GetState`) is ``NULL``.

Extension modules without module state (``m_size <= 0``) are not affected.

- bpo-38913: Fixed segfault in ``Py_BuildValue()`` called with a format
containing "#" and undefined PY_SSIZE_T_CLEAN whwn an exception is set.

- bpo-38500: Add a private API to get and set the frame evaluation function:
add :c:func:`_PyInterpreterState_GetEvalFrameFunc` and
:c:func:`_PyInterpreterState_SetEvalFrameFunc` C functions. The
:c:type:`_PyFrameEvalFunction` function type now takes a *tstate*
parameter.

What's New in Python 3.9.0 alpha 4?
===================================

*Release date: 2020-02-25*

Security
--------

- bpo-39184: Add audit events to functions in `fcntl`, `msvcrt`, `os`,
`resource`, `shutil`, `signal` and `syslog`.

- bpo-39401: Avoid unsafe DLL load at startup on Windows 7 and earlier.

- bpo-39184: Add audit events to command execution functions in os and pty
modules.

Core and Builtins
-----------------

- bpo-39382: Fix a use-after-free in the single inheritance path of
``issubclass()``, when the ``__bases__`` of an object has a single
reference, and so does its first item. Patch by Yonatan Goldschmidt.

- bpo-39573: Update clinic tool to use :c:func:`Py_IS_TYPE`. Patch by
Dong-hee Na.

- bpo-39619: Enable use of :func:`os.chroot` on HP-UX systems.

- bpo-39573: Add :c:func:`Py_IS_TYPE` static inline function to check
whether the object *o* type is *type*.

- bpo-39606: Fix regression caused by fix for bpo-39386, that prevented
calling ``aclose`` on an async generator that had already been closed or
exhausted.

- bpo-39579: Change the ending column offset of `Attribute` nodes
constructed in `ast_for_dotted_name` to point at the end of the current
node and not at the end of the last `NAME` node.

- bpo-1635741: Port _crypt extension module to multiphase initialization
(:pep:`489`).

- bpo-1635741: Port _contextvars extension module to multiphase
initialization (:pep:`489`).

- bpo-39510: Fix segfault in ``readinto()`` method on closed BufferedReader.

- bpo-39502: Fix :func:`time.localtime` on 64-bit AIX to support years
before 1902 and after 2038. Patch by M Felt.

- bpo-39492: Fix a reference cycle in the C Pickler that was preventing the
garbage collection of deleted, pickled objects.

- bpo-39453: Fixed a possible crash in :meth:`list.__contains__` when a list
is changed during comparing items. Patch by Dong-hee Na.

- bpo-39434: :term:`floor division` of float operation now has a better
performance. Also the message of :exc:`ZeroDivisionError` for this
operation is updated. Patch by Dong-hee Na.

- bpo-1635741: Port _codecs extension module to multiphase initialization
(:pep:`489`).

- bpo-1635741: Port _bz2 extension module to multiphase initialization
(:pep:`489`).

- bpo-1635741: Port _abc extension module to multiphase initialization
(:pep:`489`).

- bpo-39320: Replace two complex bytecodes for building dicts with two
simpler ones. The new bytecodes ``DICT_MERGE`` and ``DICT_UPDATE`` have
been added The old bytecodes ``BUILD_MAP_UNPACK`` and
``BUILD_MAP_UNPACK_WITH_CALL`` have been removed.

- bpo-39219: Syntax errors raised in the tokenizer now always set correct
"text" and "offset" attributes.

- bpo-36051: Drop the GIL during large ``bytes.join`` operations. Patch by
Bruce Merry.

- bpo-38960: Fix DTrace build issues on FreeBSD. Patch by David Carlier.

- bpo-37207: Speed up calls to ``range()`` by about 30%, by using the PEP
590 ``vectorcall`` calling convention. Patch by Mark Shannon.

- bpo-36144: :class:`dict` (and :class:`collections.UserDict`) objects now
support PEP 584's merge (``|``) and update (``|=``) operators. Patch by
Brandt Bucher.

- bpo-32856: Optimized the idiom for assignment a temporary variable in
comprehensions. Now ``for y in [expr]`` in comprehensions is as fast as a
simple assignment ``y = expr``.

Library
-------

- bpo-30566: Fix :exc:`IndexError` when trying to decode an invalid string
with punycode codec.

- bpo-39649: Remove obsolete check for `__args__` in
bdb.Bdb.format_stack_entry.

- bpo-39648: Expanded :func:`math.gcd` and :func:`math.lcm` to handle
multiple arguments.

- bpo-39681: Fix a regression where the C pickle module wouldn't allow
unpickling from a file-like object that doesn't expose a readinto()
method.

- bpo-35950: Raise :exc:`io.UnsupportedOperation` in
:meth:`io.BufferedReader.truncate` when it is called on a read-only
:class:`io.BufferedReader` instance.

- bpo-39479: Add :func:`math.lcm` function: least common multiple.

- bpo-39674: Revert "Do not expose abstract collection classes in the
collections module" change (bpo-25988). Aliases to ABC like
collections.Mapping are kept in Python 3.9 to ease transition from Python
2.7, but will be removed in Python 3.10.

- bpo-39104: Fix hanging ProcessPoolExcutor on ``shutdown(wait=False)`` when
a task has failed pickling.

- bpo-39627: Fixed TypedDict totality check for inherited keys.

- bpo-39474: Fixed starting position of AST for expressions like ``(a)(b)``,
``(a)[b]`` and ``(a).b``.

- bpo-21016: The :mod:`pydoc` and :mod:`trace` modules now use the
:mod:`sysconfig` module to get the path to the Python standard library, to
support uncommon installation path like ``/usr/lib64/python3.9/`` on
Fedora. Patch by Jan Matějek.

- bpo-39590: Collections.deque now holds strong references during
deque.__contains__ and deque.count, fixing crashes.

- bpo-39586: The distutils ``bdist_msi`` command is deprecated in Python
3.9, use ``bdist_wheel`` (wheel packages) instead.

- bpo-39595: Improved performance of zipfile.Path for files with a large
number of entries. Also improved performance and fixed minor issue as
published with `importlib_metadata 1.5
<https://importlib-metadata.readthedocs.io/en/latest/changelog%20(links).html#v1-5-0>`_.

- bpo-39350: Fix regression in :class:`fractions.Fraction` if the numerator
and/or the denominator is an :class:`int` subclass. The :func:`math.gcd`
function is now used to normalize the *numerator* and *denominator*.
:func:`math.gcd` always return a :class:`int` type. Previously, the GCD
type depended on *numerator* and *denominator*.

- bpo-39567: Added audit for :func:`os.walk`, :func:`os.fwalk`,
:meth:`pathlib.Path.glob` and :meth:`pathlib.Path.rglob`.

- bpo-39559: Remove unused, undocumented argument ``getters`` from
:func:`uuid.getnode`

- bpo-38149: :func:`sys.audit` is now called only once per call of
:func:`glob.glob` and :func:`glob.iglob`.

- bpo-39546: Fix a regression in :class:`~argparse.ArgumentParser` where
``allow_abbrev=False`` was ignored for long options that used a prefix
character other than "-".

- bpo-39450: Striped whitespace from docstring before returning it from
:func:`unittest.case.shortDescription`.

- bpo-12915: A new function ``resolve_name`` has been added to the
``pkgutil`` module. This resolves a string of the form ``'a.b.c.d'`` or
``'a.b:c.d'`` to an object. In the example, ``a.b`` is a package/module
and ``c.d`` is an object within that package/module reached via recursive
attribute access.

- bpo-39353: The :func:`binascii.crc_hqx` function is no longer deprecated.

- bpo-39493: Mark ``typing.IO.closed`` as a property

- bpo-39491: Add :data:`typing.Annotated` and ``include_extras`` parameter
to :func:`typing.get_type_hints` as part of :pep:`593`. Patch by Till
Varoquaux, documentation by Till Varoquaux and Konstantin Kashin.

- bpo-39485: Fix a bug in :func:`unittest.mock.create_autospec` that would
complain about the wrong number of arguments for custom descriptors
defined in an extension module returning functions.

- bpo-38932: Mock fully resets child objects on reset_mock(). Patch by
Vegard Stikbakke

- bpo-39082: Allow AsyncMock to correctly patch static/class methods

- bpo-39432: Implement PEP-489 algorithm for non-ascii "PyInit\_..." symbol
names in distutils to make it export the correct init symbol also on
Windows.

- bpo-18819: Omit ``devmajor`` and ``devminor`` fields for non-device files
in :mod:`tarfile` archives, enabling bit-for-bit compatibility with GNU
``tar(1)``.

- bpo-39349: Added a new *cancel_futures* parameter to
:meth:`concurrent.futures.Executor.shutdown` that cancels all pending
futures which have not started running, instead of waiting for them to
complete before shutting down the executor.

- bpo-39274: ``bool(fraction.Fraction)`` now returns a boolean even if
(numerator != 0) does not return a boolean (ex: numpy number).

- bpo-34793: Remove support for ``with (await asyncio.lock):`` and ``with
(yield from asyncio.lock):``. The same is correct for
``asyncio.Condition`` and ``asyncio.Semaphore``.

- bpo-25597: Ensure, if ``wraps`` is supplied to
:class:`unittest.mock.MagicMock`, it is used to calculate return values
for the magic methods instead of using the default return values. Patch by
Karthikeyan Singaravelan.

- bpo-36350: `inspect.Signature.parameters` and
`inspect.BoundArguments.arguments` are now dicts instead of OrderedDicts.
Patch contributed by Rémi Lapeyre.

- bpo-35727: Fix sys.exit() and sys.exit(None) exit code propagation when
used in multiprocessing.Process.

- bpo-32173: * Add `lazycache` function to `__all__`. * Use `dict.clear` to
clear the cache. * Refactoring `getline` function and `checkcache`
function.

Documentation
-------------

- bpo-17422: The language reference now specifies restrictions on class
namespaces. Adapted from a patch by Ethan Furman.

- bpo-39572: Updated documentation of ``total`` flag of ``TypedDict``.

- bpo-39654: In pyclbr doc, update 'class' to 'module' where appropriate and
add readmodule comment. Patch by Hakan Çelik.

- bpo-39153: Clarify refcounting semantics for the following functions: -
PyObject_SetItem - PyMapping_SetItemString - PyDict_SetItem -
PyDict_SetItemString

- bpo-39392: Explain that when filling with turtle, overlap regions may be
left unfilled.

- bpo-39369: Update mmap readline method description. The fact that the
readline method does update the file position should not be ignored since
this might give the impression for the programmer that it doesn't update
it.

- bpo-9056: Include subsection in TOC for PDF version of docs.

Tests
-----

- bpo-38325: Skip tests on non-BMP characters of test_winconsoleio.

- bpo-39502: Skip test_zipfile.test_add_file_after_2107() if
:func:`time.localtime` fails with :exc:`OverflowError`. It is the case on
AIX 6.1 for example.

Build
-----

- bpo-39489: Remove ``COUNT_ALLOCS`` special build.

Windows
-------

- bpo-39553: Delete unused code related to SxS manifests.

- bpo-39439: Honor the Python path when a virtualenv is active on Windows.

- bpo-39393: Improve the error message when attempting to load a DLL with
unresolved dependencies.

- bpo-38883: :meth:`~pathlib.Path.home()` and
:meth:`~pathlib.Path.expanduser()` on Windows now prefer
:envvar:`USERPROFILE` and no longer use :envvar:`HOME`, which is not
normally set for regular user accounts. This makes them again behave like
:func:`os.path.expanduser`, which was changed to ignore :envvar:`HOME` in
3.8, see :issue:`36264`.

- bpo-39185: The build.bat script has additional options for very-quiet
output (-q) and very-verbose output (-vv)

IDLE
----

- bpo-39663: Add tests for pyparse find_good_parse_start().

- bpo-39600: In the font configuration window, remove duplicated font names.

- bpo-30780: Add remaining configdialog tests for buttons and highlights and
keys tabs.

- bpo-39388: IDLE Settings Cancel button now cancels pending changes

- bpo-38792: Close an IDLE shell calltip if a :exc:`KeyboardInterrupt` or
shell restart occurs. Patch by Zackery Spytz.

C API
-----

- bpo-35081: Move the ``bytes_methods.h`` header file to the internal C API
as ``pycore_bytes_methods.h``: it only contains private symbols (prefixed
by ``_Py``), except of the ``PyDoc_STRVAR_shared()`` macro.

- bpo-35081: Move the ``dtoa.h`` header file to the internal C API as
``pycore_dtoa.h``: it only contains private functions (prefixed by
``_Py``). The :mod:`math` and :mod:`cmath` modules must now be compiled
with the ``Py_BUILD_CORE`` macro defined.

- bpo-39573: Add :c:func:`Py_SET_SIZE` function to set the size of an
object.

- bpo-39500: :c:func:`PyUnicode_IsIdentifier` does not call
:c:func:`Py_FatalError` anymore if the string is not ready.

- bpo-39573: Add :c:func:`Py_SET_TYPE` function to set the type of an
object.

- bpo-39573: Add a :c:func:`Py_SET_REFCNT` function to set the reference
counter of an object.

- bpo-39542: Convert :c:func:`PyType_HasFeature`, :c:func:`PyType_Check` and
:c:func:`PyType_CheckExact` macros to static inline functions.

- bpo-39542: In the limited C API, ``PyObject_INIT()`` and
``PyObject_INIT_VAR()`` are now defined as aliases to
:c:func:`PyObject_Init` and :c:func:`PyObject_InitVar` to make their
implementation opaque. It avoids to leak implementation details in the
limited C API. Exclude the following functions from the limited C API:
``_Py_NewReference()``, ``_Py_ForgetReference()``,
``_PyTraceMalloc_NewReference()`` and ``_Py_GetRefTotal()``.

- bpo-39542: Exclude trashcan mechanism from the limited C API: it requires
access to PyTypeObject and PyThreadState structure fields, whereas these
structures are opaque in the limited C API.

- bpo-39511: The :c:func:`PyThreadState_Clear` function now calls the
:c:member:`PyThreadState.on_delete` callback. Previously, that happened in
:c:func:`PyThreadState_Delete`.

- bpo-38076: Fix to clear the interpreter state only after clearing module
globals to guarantee module state access from C Extensions during runtime
destruction

- bpo-39245: The Vectorcall API (PEP 590) was made public, adding the
functions ``PyObject_Vectorcall``, ``PyObject_VectorcallMethod``,
``PyVectorcall_Function``, ``PyObject_CallOneArg``,
``PyObject_CallMethodNoArgs``, ``PyObject_CallMethodOneArg``,
``PyObject_FastCallDict``, and the flag ``Py_TPFLAGS_HAVE_VECTORCALL``.

What's New in Python 3.9.0 alpha 3?
===================================

*Release date: 2020-01-24*

Core and Builtins
-----------------

- bpo-39427: Document all possibilities for the ``-X`` options in the
command line help section. Patch by Pablo Galindo.

- bpo-39421: Fix possible crashes when operating with the functions in the
:mod:`heapq` module and custom comparison operators.

- bpo-39386: Prevent double awaiting of async iterator.

- bpo-17005: Add :class:`functools.TopologicalSorter` to the
:mod:`functools` module to offers functionality to perform topological
sorting of graphs. Patch by Pablo Galindo, Tim Peters and Larry Hastings.

- bpo-39320: Replace four complex bytecodes for building sequences with
three simpler ones.

The following four bytecodes have been removed:

* BUILD_LIST_UNPACK
* BUILD_TUPLE_UNPACK
* BUILD_SET_UNPACK
* BUILD_TUPLE_UNPACK_WITH_CALL

The following three bytecodes have been added:

* LIST_TO_TUPLE
* LIST_EXTEND
* SET_UPDATE

- bpo-39336: Import loaders which publish immutable module objects can now
publish immutable packages in addition to individual modules.

- bpo-39322: Added a new function :func:`gc.is_finalized` to check if an
object has been finalized by the garbage collector. Patch by Pablo
Galindo.

- bpo-39048: Improve the displayed error message when incorrect types are
passed to ``async with`` statements by looking up the :meth:`__aenter__`
special method before the :meth:`__aexit__` special method when entering
an asynchronous context manager. Patch by Géry Ogam.

- bpo-39235: Fix AST end location for lone generator expression in function
call, e.g. f(i for i in a).

- bpo-39209: Correctly handle multi-line tokens in interactive mode. Patch
by Pablo Galindo.

- bpo-1635741: Port _json extension module to multiphase initialization
(:pep:`489`).

- bpo-39216: Fix constant folding optimization for positional only arguments
- by Anthony Sottile.

- bpo-39215: Fix ``SystemError`` when nested function has annotation on
positional-only argument - by Anthony Sottile.

- bpo-39200: Correct the error message when calling the :func:`min` or
:func:`max` with no arguments. Patch by Dong-hee Na.

- bpo-39200: Correct the error message when trying to construct
:class:`range` objects with no arguments. Patch by Pablo Galindo.

- bpo-39166: Fix incorrect line execution reporting in trace functions when
tracing the last iteration of asynchronous for loops. Patch by Pablo
Galindo.

- bpo-39114: Fix incorrect line execution reporting in trace functions when
tracing exception handlers with name binding. Patch by Pablo Galindo.

- bpo-39156: Split the COMPARE_OP bytecode instruction into four distinct
instructions.

* COMPARE_OP for rich comparisons
* IS_OP for 'is' and 'is not' tests
* CONTAINS_OP for 'in' and 'is not' tests
* JUMP_IF_NOT_EXC_MATCH for checking exceptions in 'try-except' statements.

This improves the clarity of the interpreter and should provide a modest
speedup.

- bpo-38588: Fix possible crashes in dict and list when calling
:c:func:`PyObject_RichCompareBool`.

- bpo-13601: By default, ``sys.stderr`` is line-buffered now, even if
``stderr`` is redirected to a file. You can still make ``sys.stderr``
unbuffered by passing the :option:`-u` command-line option or setting the
:envvar:`PYTHONUNBUFFERED` environment variable.

(Contributed by Jendrik Seipp in bpo-13601.)

- bpo-38610: Fix possible crashes in several list methods by holding strong
references to list elements when calling
:c:func:`PyObject_RichCompareBool`.

- bpo-32021: Include brotli .br encoding in mimetypes encodings_map

Library
-------

- bpo-39430: Fixed race condition in lazy imports in :mod:`tarfile`.

- bpo-39413: The :func:`os.unsetenv` function is now also available on
Windows.

- bpo-39390: Fixed a regression with the `ignore` callback of
:func:`shutil.copytree`. The argument types are now str and List[str]
again.

- bpo-39395: The :func:`os.putenv` and :func:`os.unsetenv` functions are now
always available.

- bpo-39406: If ``setenv()`` C function is available, :func:`os.putenv` is
now implemented with ``setenv()`` instead of ``putenv()``, so Python
doesn't have to handle the environment variable memory.

- bpo-39396: Fix ``math.nextafter(-0.0, +0.0)`` on AIX 7.1.

- bpo-29435: Allow :func:`tarfile.is_tarfile` to be used with file and
file-like objects, like :func:`zipfile.is_zipfile`. Patch by William
Woodruff.

- bpo-39377: Removed ``encoding`` option from :func:`json.loads`. It has
been deprecated since Python 3.1.

- bpo-39389: Write accurate compression level metadata in :mod:`gzip`
archives, rather than always signaling maximum compression.

- bpo-39366: The previously deprecated ``xpath()`` and ``xgtitle()`` methods
of :class:`nntplib.NNTP` have been removed.

- bpo-39357: Remove the *buffering* parameter of :class:`bz2.BZ2File`. Since
Python 3.0, it was ignored and using it was emitting
:exc:`DeprecationWarning`. Pass an open file object, to control how the
file is opened. The *compresslevel* parameter becomes keyword-only.

- bpo-39353: Deprecate binhex4 and hexbin4 standards. Deprecate the
:mod:`binhex` module and the following :mod:`binascii` functions:
:func:`~binascii.b2a_hqx`, :func:`~binascii.a2b_hqx`,
:func:`~binascii.rlecode_hqx`, :func:`~binascii.rledecode_hqx`,
:func:`~binascii.crc_hqx`.

- bpo-39351: Remove ``base64.encodestring()`` and ``base64.decodestring()``,
aliases deprecated since Python 3.1: use :func:`base64.encodebytes` and
:func:`base64.decodebytes` instead.

- bpo-39350: Remove ``fractions.gcd()`` function, deprecated since Python
3.5 (:issue:`22486`): use :func:`math.gcd` instead.

- bpo-39329: :class:`~smtplib.LMTP` constructor now has an optional
*timeout* parameter. Patch by Dong-hee Na.

- bpo-39313: Add a new ``exec_function`` option (*--exec-function* in the
CLI) to ``RefactoringTool`` for making ``exec`` a function. Patch by
Batuhan Taskaya.

- bpo-39259: :class:`~ftplib.FTP_TLS` and :class:`~ftplib.FTP_TLS` now raise
a :class:`ValueError` if the given timeout for their constructor is zero
to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-39259: :class:`~smtplib.SMTP` and :class:`~smtplib.SMTP_SSL` now raise
a :class:`ValueError` if the given timeout for their constructor is zero
to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-39310: Add :func:`math.ulp`: return the value of the least significant
bit of a float.

- bpo-39297: Improved performance of importlib.metadata distribution
discovery and resilients to inaccessible sys.path entries
(importlib_metadata v1.4.0).

- bpo-39259: :class:`~nntplib.NNTP` and :class:`~nntplib.NNTP_SSL` now raise
a :class:`ValueError` if the given timeout for their constructor is zero
to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-38901: When you specify prompt='.' or equivalently python -m venv
--prompt . ... the basename of the current directory is used to set the
created venv's prompt when it's activated.

- bpo-39288: Add :func:`math.nextafter`: return the next floating-point
value after *x* towards *y*.

- bpo-39259: :class:`~poplib.POP3` and :class:`~poplib.POP3_SSL` now raise a
:class:`ValueError` if the given timeout for their constructor is zero to
prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-39242: Updated the Gmane domain from news.gmane.org to news.gmane.io
which is used for examples of :class:`~nntplib.NNTP` news reader server
and nntplib tests.

- bpo-35292: Proxy the `SimpleHTTPRequestHandler.guess_type` to
`mimetypes.guess_type` so the `mimetypes.init` is called lazily to avoid
unnecessary costs when :mod:`http.server` module is imported.

- bpo-39239: The :meth:`select.epoll.unregister` method no longer ignores
the :data:`~errno.EBADF` error.

- bpo-38907: In http.server script, restore binding to IPv4 on Windows.

- bpo-39152: Fix ttk.Scale.configure([name]) to return configuration tuple
for name or all options. Giovanni Lombardo contributed part of the patch.

- bpo-39198: If an exception were to be thrown in `Logger.isEnabledFor`
(say, by asyncio timeouts or stopit) , the `logging` global lock may not
be released appropriately, resulting in deadlock. This change wraps that
block of code with `try...finally` to ensure the lock is released.

- bpo-39191: Perform a check for running loop before starting a new task in
``loop.run_until_complete()`` to fail fast; it prevents the side effect of
new task spawning before exception raising.

- bpo-38871: Correctly parenthesize filter-based statements that contain
lambda expressions in mod:`lib2to3`. Patch by Dong-hee Na.

- bpo-39142: A change was made to logging.config.dictConfig to avoid
converting instances of named tuples to ConvertingTuple. It's assumed that
named tuples are too specialised to be treated like ordinary tuples; if a
user of named tuples requires ConvertingTuple functionality, they will
have to implement that themselves in their named tuple class.

- bpo-39158: ast.literal_eval() now supports empty sets.

- bpo-39129: Fix import path for ``asyncio.TimeoutError``

- bpo-39057: :func:`urllib.request.proxy_bypass_environment` now ignores
leading dots and no longer ignores a trailing newline.

- bpo-39056: Fixed handling invalid warning category in the -W option. No
longer import the re module if it is not needed.

- bpo-39055: :func:`base64.b64decode` with ``validate=True`` raises now a
binascii.Error if the input ends with a single ``\n``.

- bpo-21600: Fix :func:`mock.patch.stopall` to stop active patches that were
created with :func:`mock.patch.dict`.

- bpo-39019: Implement dummy ``__class_getitem__`` for
:class:`tempfile.SpooledTemporaryFile`.

- bpo-39019: Implement dummy ``__class_getitem__`` for ``subprocess.Popen``,
``subprocess.CompletedProcess``

- bpo-38914: Adjusted the wording of the warning issued by distutils'
``check`` command when the ``author`` and ``maintainer`` fields are
supplied but no corresponding e-mail field (``author_email`` or
``maintainer_email``) is found. The wording now reflects the fact that
these fields are suggested, but not required. Patch by Juergen Gmach.

- bpo-38878: Fixed __subclasshook__ of :class:`os.PathLike` to return a
correct result upon inheritance. Patch by Bar Harel.

- bpo-38615: :class:`~imaplib.IMAP4` and :class:`~imaplib.IMAP4_SSL` now
have an optional *timeout* parameter for their constructors. Also, the
:meth:`~imaplib.IMAP4.open` method now has an optional *timeout* parameter
with this change. The overridden methods of :class:`~imaplib.IMAP4_SSL`
and :class:`~imaplib.IMAP4_stream` were applied to this change. Patch by
Dong-hee Na.

- bpo-35182: Fixed :func:`Popen.communicate` subsequent call crash when the
child process has already closed any piped standard stream, but still
continues to be running. Patch by Andriy Maletsky.

- bpo-38630: On Unix, :meth:`subprocess.Popen.send_signal` now polls the
process status. Polling reduces the risk of sending a signal to the wrong
process if the process completed, the :attr:`subprocess.Popen.returncode`
attribute is still ``None``, and the pid has been reassigned (recycled) to
a new different process.

- bpo-38536: Removes trailing space in formatted currency with
`international=True` and a locale with symbol following value. E.g.
`locale.currency(12.34, international=True)` returned `'12,34 EUR '`
instead of `'12,34 EUR'`.

- bpo-38473: Use signature from inner mock for autospecced methods attached
with :func:`unittest.mock.attach_mock`. Patch by Karthikeyan Singaravelan.

- bpo-38361: Fixed an issue where ``ident`` could include a leading path
separator when :func:`syslog.openlog` was called without arguments.

- bpo-38293: Add :func:`copy.copy` and :func:`copy.deepcopy` support to
:func:`property` objects.

- bpo-37958: Added the pstats.Stats.get_profile_dict() method to return the
profile data as a StatsProfile instance.

- bpo-28367: Termios magic constants for the following baud rates: -
B500000 - B576000 - B921600 - B1000000 - B1152000 - B1500000 -
B2000000 - B2500000 - B3000000 - B3500000 - B4000000 Patch by
Andrey Smirnov

Documentation
-------------

- bpo-39381: Mention in docs that :func:`asyncio.get_event_loop` implicitly
creates new event loop only if called from the main thread.

- bpo-38918: Add an entry for ``__module__`` in the "function" & "method"
sections of the :mod:`inspect` docs' :ref:`inspect-types` table.

- bpo-3530: In the :mod:`ast` module documentation, fix a misleading
``NodeTransformer`` example and add advice on when to use the
``fix_missing_locations`` function.

Build
-----

- bpo-39395: On non-Windows platforms, the :c:func:`setenv` and
:c:func:`unsetenv` functions are now required to build Python.

- bpo-39160: Updated the documentation in `./configure --help` to show
default values, reference documentation where required and add additional
explanation where needed.

- bpo-39144: The ctags and etags build targets both include Modules/_ctypes
and Python standard library source files.

IDLE
----

- bpo-39050: Make IDLE Settings dialog Help button work again.

- bpo-34118: Tag memoryview, range, and tuple as classes, the same as list,
etcetera, in the library manual built-in functions list.

- bpo-32989: Add tests for editor newline_and_indent_event method. Remove
dead code from pyparse find_good_parse_start method.

C API
-----

- bpo-39372: Clean header files of interfaces defined but with no
implementation. The public API symbols being removed are:
``_PyBytes_InsertThousandsGroupingLocale``,
``_PyBytes_InsertThousandsGrouping``, ``_Py_InitializeFromArgs``,
``_Py_InitializeFromWideArgs``, ``_PyFloat_Repr``, ``_PyFloat_Digits``,
``_PyFloat_DigitsInit``, ``PyFrame_ExtendStack``,
``_PyAIterWrapper_Type``, ``PyNullImporter_Type``, ``PyCmpWrapper_Type``,
``PySortWrapper_Type``, ``PyNoArgsFunction``.

- bpo-39164: Add a private ``_PyErr_GetExcInfo()`` function to retrieve
exception information of the specified Python thread state.

What's New in Python 3.9.0 alpha 2?
===================================

*Release date: 2019-12-18*

Security
--------

- bpo-38945: Newline characters have been escaped when performing uu
encoding to prevent them from overflowing into to content section of the
encoded file. This prevents malicious or accidental modification of data
during the decoding process.

- bpo-37228: Due to significant security concerns, the *reuse_address*
parameter of :meth:`asyncio.loop.create_datagram_endpoint` is no longer
supported. This is because of the behavior of ``SO_REUSEADDR`` in UDP. For
more details, see the documentation for
``loop.create_datagram_endpoint()``. (Contributed by Kyle Stanley, Antoine
Pitrou, and Yury Selivanov in :issue:`37228`.)

- bpo-38804: Fixes a ReDoS vulnerability in :mod:`http.cookiejar`. Patch by
Ben Caller.

Core and Builtins
-----------------

- bpo-39028: Slightly improve the speed of keyword argument parsing with
many kwargs by strengthening the assumption that kwargs are interned
strings.

- bpo-39080: Fix the value of *end_col_offset* for Starred Expression AST
nodes when they are among the elements in the *args* attribute of Call AST
nodes.

- bpo-39031: When parsing an "elif" node, lineno and col_offset of the node
now point to the "elif" keyword and not to its condition, making it
consistent with the "if" node. Patch by Lysandros Nikolaou.

- bpo-20443: In Python 3.9.0a1, sys.argv[0] was made an absolute path if a
filename was specified on the command line. Revert this change, since most
users expect sys.argv to be unmodified.

- bpo-39008: :c:func:`PySys_Audit` now requires ``Py_ssize_t`` to be used
for size arguments in the format string, regardless of whether
``PY_SSIZE_T_CLEAN`` was defined at include time.

- bpo-38673: In REPL mode, don't switch to PS2 if the line starts with
comment or whitespace. Based on work by Batuhan Taşkaya.

- bpo-38922: Calling ``replace`` on a code object now raises the
``code.__new__`` audit event.

- bpo-38920: Add audit hooks for when :func:`sys.excepthook` and
:func:`sys.unraisablehook` are invoked.

- bpo-38892: Improve documentation for audit events table and functions.

- bpo-38852: Set the thread stack size to 8 Mb for debug builds on android
platforms.

- bpo-38858: Each Python subinterpreter now has its own "small integer
singletons": numbers in [-5; 257] range. It is no longer possible to
change the number of small integers at build time by overriding
``NSMALLNEGINTS`` and ``NSMALLPOSINTS`` macros: macros should now be
modified manually in ``pycore_pystate.h`` header file.

- bpo-36854: The garbage collector state becomes per interpreter
(``PyInterpreterState.gc``), rather than being global
(``_PyRuntimeState.gc``).

- bpo-38835: The ``PyFPE_START_PROTECT()`` and ``PyFPE_END_PROTECT()``
macros are empty: they have been doing nothing for the last year, so stop
using them.

- bpo-38328: Sped up the creation time of constant :class:`list` and
:class:`set` displays. Patch by Brandt Bucher.

- bpo-38707: ``MainThread.native_id`` is now correctly reset in child
processes spawned using :class:`multiprocessing.Process`, instead of
retaining the parent's value.

- bpo-38629: Added ``__floor__`` and ``__ceil__`` methods to float object.
Patch by Batuhan Taşkaya.

- bpo-27145: int + int and int - int operators can now return small integer
singletons. Patch by hongweipeng.

- bpo-38021: Provide a platform tag for AIX that is sufficient for PEP425
binary distribution identification. Patch by Michael Felt.

- bpo-35409: Ignore GeneratorExit exceptions when throwing an exception into
the aclose coroutine of an asynchronous generator.

- bpo-33387: Removed WITH_CLEANUP_START, WITH_CLEANUP_FINISH, BEGIN_FINALLY,
END_FINALLY, CALL_FINALLY and POP_FINALLY bytecodes. Replaced with RERAISE
and WITH_EXCEPT_START bytecodes. The compiler now generates different code
for exceptional and non-exceptional branches for 'with' and 'try-except'
statements. For 'try-finally' statements the 'finally' block is replicated
for each exit from the 'try' body.

Library
-------

- bpo-39033: Fix :exc:`NameError` in :mod:`zipimport`. Patch by Karthikeyan
Singaravelan.

- bpo-39022: Update importlib.metadata to include improvements from
importlib_metadata 1.3 including better serialization of EntryPoints and
improved documentation for custom finders.

- bpo-39006: Fix asyncio when the ssl module is missing: only check for
ssl.SSLSocket instance if the ssl module is available.

- bpo-38708: Fix a potential IndexError in email parser when parsing an
empty msg-id.

- bpo-38698: Add a new ``InvalidMessageID`` token to email parser to
represent invalid Message-ID headers. Also, add defects when there is
remaining value after parsing the header.

- bpo-38994: Implement ``__class_getitem__`` for ``os.PathLike``,
``pathlib.Path``.

- bpo-38979: Return class from ``ContextVar.__class_getitem__`` to simplify
subclassing.

- bpo-38978: Implement ``__class_getitem__`` on asyncio objects (Future,
Task, Queue). Patch by Batuhan Taskaya.

- bpo-38916: :class:`array.array`: Remove ``tostring()`` and
``fromstring()`` methods. They were aliases to ``tobytes()`` and
``frombytes()``, deprecated since Python 3.2.

- bpo-38986: Make repr of C accelerated TaskWakeupMethWrapper the same as of
pure Python version.

- bpo-38982: Fix asyncio ``PidfdChildWatcher``: handle ``waitpid()`` error.
If ``waitpid()`` is called elsewhere, ``waitpid()`` call fails with
:exc:`ChildProcessError`: use return code 255 in this case, and log a
warning. It ensures that the pidfd file descriptor is closed if this error
occurs.

- bpo-38529: Drop too noisy asyncio warning about deletion of a stream
without explicit ``.close()`` call.

- bpo-27413: Added ability to pass through ``ensure_ascii`` options to
json.dumps in the ``json.tool`` command-line interface.

- bpo-38634: The :mod:`readline` module now detects if Python is linked to
libedit at runtime on all platforms. Previously, the check was only done
on macOS.

- bpo-33684: Fix ``json.tool`` failed to read a JSON file with non-ASCII
characters when locale encoding is not UTF-8.

- bpo-38698: Prevent UnboundLocalError to pop up in parse_message_id.

parse_message_id() was improperly using a token defined inside an
exception handler, which was raising `UnboundLocalError` on parsing an
invalid value. Patch by Claudiu Popa.

- bpo-38927: Use ``python -m pip`` instead of ``pip`` to upgrade
dependencies in venv.

- bpo-26730: Fix ``SpooledTemporaryFile.rollover()`` might corrupt the file
when it is in text mode. Patch by Serhiy Storchaka.

- bpo-38881: random.choices() now raises a ValueError when all the weights
are zero.

- bpo-38876: Raise pickle.UnpicklingError when loading an item from memo for
invalid input.

The previous code was raising a `KeyError` for both the Python and C
implementation. This was caused by the specified index of an invalid input
which did not exist in the memo structure, where the pickle stores what
objects it has seen. The malformed input would have caused either a
`BINGET` or `LONG_BINGET` load from the memo, leading to a `KeyError` as
the determined index was bogus. Patch by Claudiu Popa

- bpo-38688: Calling func:`shutil.copytree` to copy a directory tree from
one directory to another subdirectory resulted in an endless loop and a
RecursionError. A fix was added to consume an iterator and create the list
of the entries to be copied, avoiding the recursion for newly created
directories. Patch by Bruno P. Kinoshita.

- bpo-38863: Improve :func:`is_cgi` function in :mod:`http.server`, which
enables processing the case that cgi directory is a child of another
directory other than root.

- bpo-37838: :meth:`typing.get_type_hints` properly handles functions
decorated with :meth:`functools.wraps`.

- bpo-38870: Expose :func:`ast.unparse` as a function of the :mod:`ast`
module that can be used to unparse an :class:`ast.AST` object and produce
a string with code that would produce an equivalent :class:`ast.AST`
object when parsed. Patch by Pablo Galindo and Batuhan Taskaya.

- bpo-38859: AsyncMock now returns StopAsyncIteration on the exhaustion of a
side_effects iterable. Since PEP-479 its Impossible to raise a
StopIteration exception from a coroutine.

- bpo-38857: AsyncMock fix for return values that are awaitable types. This
also covers side_effect iterable values that happened to be awaitable, and
wraps callables that return an awaitable type. Before these awaitables
were being awaited instead of being returned as is.

- bpo-38834: :class:`typing.TypedDict` subclasses now track which keys are
optional using the ``__required_keys__`` and ``__optional_keys__``
attributes, to enable runtime validation by downstream projects. Patch by
Zac Hatfield-Dodds.

- bpo-38821: Fix unhandled exceptions in :mod:`argparse` when
internationalizing error messages for arguments with ``nargs`` set to
special (non-integer) values. Patch by Federico Bond.

- bpo-38820: Make Python compatible with OpenSSL 3.0.0.
:func:`ssl.SSLSocket.getpeercert` no longer returns IPv6 addresses with a
trailing new line.

- bpo-38811: Fix an unhandled exception in :mod:`pathlib` when
:meth:`os.link` is missing. Patch by Toke Høiland-Jørgensen.

- bpo-38686: Added support for multiple ``qop`` values in
:class:`urllib.request.AbstractDigestAuthHandler`.

- bpo-38712: Add the Linux-specific :func:`signal.pidfd_send_signal`
function, which allows sending a signal to a process identified by a file
descriptor rather than a pid.

- bpo-38348: Add ``-i`` and ``--indent`` (indentation level), and
``--no-type-comments`` (type comments) command line options to ast parsing
tool.

- bpo-37523: Change :class:`zipfile.ZipExtFile` to raise ``ValueError`` when
trying to access the underlying file object after it has been closed. This
new behavior is consistent with how accessing closed files is handled in
other parts of Python.

- bpo-38045: Improve the performance of :func:`enum._decompose` in
:mod:`enum`. Patch by hongweipeng.

- bpo-36820: Break cycle generated when saving an exception in socket.py,
codeop.py and dyld.py as they keep alive not only the exception but user
objects through the ``__traceback__`` attribute. Patch by Mario Corchero.

- bpo-36406: Handle namespace packages in :mod:`doctest`. Patch by
Karthikeyan Singaravelan.

- bpo-34776: Fix dataclasses to support forward references in type
annotations

- bpo-20928: ElementTree supports recursive XInclude processing. Patch by
Stefan Behnel.

- bpo-29636: Add whitespace options for formatting JSON with the
``json.tool`` CLI. The following mutually exclusive options are now
supported: ``--indent`` for setting the indent level in spaces; ``--tab``
for indenting with tabs; ``--no-indent`` for suppressing newlines; and
``--compact`` for suppressing all whitespace. The default behavior remains
the same as ``--indent=4``.

Documentation
-------------

- bpo-38928: Correct when venv's ``upgrade_dependencies()`` and
``--upgrade-deps`` are added.

- bpo-38899: Update documentation to state that to activate virtual
environments under fish one should use `source`, not `.` as documented at
https://fishshell.com/docs/current/commands.html#source.

- bpo-22377: Improves documentation of the values that
:meth:`datetime.datetime.strptime` accepts for ``%Z``. Patch by Karl
Dubost.

Tests
-----

- bpo-38546: Fix test_ressources_gced_in_workers() of
test_concurrent_futures: explicitly stop the manager to prevent leaking a
child process running in the background after the test completes.

- bpo-38546: Multiprocessing and concurrent.futures tests now stop the
resource tracker process when tests complete.

- bpo-38614: Replace hardcoded timeout constants in tests with new
:mod:`test.support` constants: :data:`~test.support.LOOPBACK_TIMEOUT`,
:data:`~test.support.INTERNET_TIMEOUT`,
:data:`~test.support.SHORT_TIMEOUT` and
:data:`~test.support.LONG_TIMEOUT`. It becomes easier to adjust these four
timeout constants for all tests at once, rather than having to adjust
every single test file.

- bpo-38547: Fix test_pty: if the process is the session leader, closing the
master file descriptor raises a SIGHUP signal: simply ignore SIGHUP when
running the tests.

- bpo-38992: Fix a test for :func:`math.fsum` that was failing due to
constant folding.

- bpo-38991: :mod:`test.support`:
:func:`~test.support.run_python_until_end`,
:func:`~test.support.assert_python_ok` and
:func:`~test.support.assert_python_failure` functions no longer strip
whitespaces from stderr. Remove ``test.support.strip_python_stderr()``
function.

- bpo-38965: Fix test_faulthandler on GCC 10. Use the "volatile" keyword in
``faulthandler._stack_overflow()`` to prevent tail call optimization on
any compiler, rather than relying on compiler specific pragma.

- bpo-38875: test_capi: trashcan tests now require the test "cpu" resource.

- bpo-38841: Skip asyncio test_create_datagram_endpoint_existing_sock_unix
on platforms lacking a functional bind() for named unix domain sockets.

- bpo-38692: Skip the test_posix.test_pidfd_open() test if
``os.pidfd_open()`` fails with a :exc:`PermissionError`. This situation
can happen in a Linux sandbox using a syscall whitelist which doesn't
allow the ``pidfd_open()`` syscall yet.

- bpo-38839: Fix some unused functions in tests. Patch by Adam Johnson.

- bpo-38669: Raise :exc:`TypeError` when passing target as a string with
:meth:`unittest.mock.patch.object`.

- bpo-37957: test.regrtest now can receive a list of test patterns to ignore
(using the -i/--ignore argument) or a file with a list of patterns to
ignore (using the --ignore-file argument). Patch by Pablo Galindo.

Build
-----

- bpo-37404: :mod:`asyncio` now raises :exc:`TyperError` when calling
incompatible methods with an :class:`ssl.SSLSocket` socket. Patch by Ido
Michael.

- bpo-36500: Added an optional "regen" project to the Visual Studio solution
that will regenerate all grammar, tokens, and opcodes.

Windows
-------

- bpo-39007: Add auditing events to functions in :mod:`winreg`.

- bpo-33125: Add support for building and releasing Windows ARM64 packages.

macOS
-----

- bpo-37931: Fixed a crash on OSX dynamic builds that occurred when
re-initializing the posix module after a Py_Finalize if the environment
had changed since the previous `import posix`. Patch by Benoît Hudson.

IDLE
----

- bpo-38944: Escape key now closes IDLE completion windows. Patch by Johnny
Najera.

- bpo-38943: Fix IDLE autocomplete windows not always appearing on some
systems. Patch by Johnny Najera.

- bpo-38862: 'Strip Trailing Whitespace' on the Format menu removes extra
newlines at the end of non-shell files.

- bpo-38636: Fix IDLE Format menu tab toggle and file indent width. These
functions (default shortcuts Alt-T and Alt-U) were mistakenly disabled in
3.7.5 and 3.8.0.

C API
-----

- bpo-38896: Remove ``PyUnicode_ClearFreeList()`` function: the Unicode free
list has been removed in Python 3.3.

- bpo-37340: Remove ``PyMethod_ClearFreeList()`` and
``PyCFunction_ClearFreeList()`` functions: the free lists of bound method
objects have been removed.

- bpo-38835: Exclude ``PyFPE_START_PROTECT()`` and ``PyFPE_END_PROTECT()``
macros of ``pyfpe.h`` from ``Py_LIMITED_API`` (stable API).

What's New in Python 3.9.0 alpha 1?
===================================

*Release date: 2019-11-19*

Security
--------

- bpo-38722: :mod:`runpy` now uses :meth:`io.open_code` to open code files.
Patch by Jason Killen.

- bpo-38622: Add additional audit events for the :mod:`ctypes` module.

- bpo-38418: Fixes audit event for :func:`os.system` to be named
``os.system``.

- bpo-38243: Escape the server title of
:class:`xmlrpc.server.DocXMLRPCServer` when rendering the document page as
HTML. (Contributed by Dong-hee Na in :issue:`38243`.)

- bpo-38174: Update vendorized expat library version to 2.2.8, which
resolves CVE-2019-15903.

- bpo-37764: Fixes email._header_value_parser.get_unstructured going into an
infinite loop for a specific case in which the email header does not have
trailing whitespace, and the case in which it contains an invalid encoded
word. Patch by Ashwin Ramaswami.

- bpo-37461: Fix an infinite loop when parsing specially crafted email
headers. Patch by Abhilash Raj.

- bpo-37363: Adds audit events for the range of supported run commands (see
:ref:`using-on-general`).

- bpo-37463: ssl.match_hostname() no longer accepts IPv4 addresses with
additional text after the address and only quad-dotted notation without
trailing whitespaces. Some inet_aton() implementations ignore whitespace
and all data after whitespace, e.g. '127.0.0.1 whatever'.

- bpo-37363: Adds audit events for :mod:`ensurepip`, :mod:`ftplib`,
:mod:`glob`, :mod:`imaplib`, :mod:`nntplib`, :mod:`pdb`, :mod:`poplib`,
:mod:`shutil`, :mod:`smtplib`, :mod:`sqlite3`, :mod:`subprocess`,
:mod:`telnetlib`, :mod:`tempfile` and :mod:`webbrowser`, as well as
:func:`os.listdir`, :func:`os.scandir` and :func:`breakpoint`.

- bpo-37364: :func:`io.open_code` is now used when reading :file:`.pth`
files.

- bpo-34631: Updated OpenSSL to 1.1.1c in Windows installer

- bpo-34155: Fix parsing of invalid email addresses with more than one ``@``
(e.g. a@b@c.com.) to not return the part before 2nd ``@`` as valid email
address. Patch by maxking & jpic.

Core and Builtins
-----------------

- bpo-38631: Replace ``Py_FatalError()`` call with a regular
:exc:`RuntimeError` exception in :meth:`float.__getformat__`.

- bpo-38639: Optimized :func:`math.floor()`, :func:`math.ceil()` and
:func:`math.trunc()` for floats.

- bpo-38640: Fixed a bug in the compiler that was causing to raise in the
presence of break statements and continue statements inside always false
while loops. Patch by Pablo Galindo.

- bpo-38613: Optimized some set operations (e.g. ``|``, ``^``, and ``-``) of
``dict_keys``. ``d.keys() | other`` was slower than ``set(d) | other`` but
they are almost same performance for now.

- bpo-28029: ``"".replace("", s, n)`` now returns ``s`` instead of an empty
string for all non-zero ``n``. There are similar changes for
:class:`bytes` and :class:`bytearray` objects.

- bpo-38535: Fixed line numbers and column offsets for AST nodes for calls
without arguments in decorators.

- bpo-38525: Fix a segmentation fault when using reverse iterators of empty
``dict`` objects. Patch by Dong-hee Na and Inada Naoki.

- bpo-38465: :class:`bytearray`, :class:`~array.array` and
:class:`~mmap.mmap` objects allow now to export more than ``2**31``
buffers at a time.

- bpo-38469: Fixed a bug where the scope of named expressions was not being
resolved correctly in the presence of the *global* keyword. Patch by Pablo
Galindo.

- bpo-38437: Activate the ``GC_DEBUG`` macro for debug builds of the
interpreter (when ``Py_DEBUG`` is set). Patch by Pablo Galindo.

- bpo-38379: When the garbage collector makes a collection in which some
objects resurrect (they are reachable from outside the isolated cycles
after the finalizers have been executed), do not block the collection of
all objects that are still unreachable. Patch by Pablo Galindo and Tim
Peters.

- bpo-38379: When cyclic garbage collection (gc) runs finalizers that
resurrect unreachable objects, the current gc run ends, without collecting
any cyclic trash. However, the statistics reported by ``collect()`` and
``get_stats()`` claimed that all cyclic trash found was collected, and
that the resurrected objects were collected. Changed the stats to report
that none were collected.

- bpo-38392: In debug mode, :c:func:`PyObject_GC_Track` now calls
``tp_traverse()`` of the object type to ensure that the object is valid:
test that objects visited by ``tp_traverse()`` are valid.

- bpo-38210: Remove unnecessary intersection and update set operation in
dictview with empty set. (Contributed by Dong-hee Na in :issue:`38210`.)

- bpo-38402: Check the error from the system's underlying ``crypt`` or
``crypt_r``.

- bpo-37474: On FreeBSD, Python no longer calls ``fedisableexcept()`` at
startup to control the floating point control mode. The call became
useless since FreeBSD 6: it became the default mode.

- bpo-38006: Fix a bug due to the interaction of weakrefs and the cyclic
garbage collector. We must clear any weakrefs in garbage in order to
prevent their callbacks from executing and causing a crash.

- bpo-38317: Fix warnings options priority: ``PyConfig.warnoptions`` has the
highest priority, as stated in the :pep:`587`.

- bpo-38310: Predict ``BUILD_MAP_UNPACK_WITH_CALL`` -> ``CALL_FUNCTION_EX``
opcode pairs in the main interpreter loop. Patch by Brandt Bucher.

- bpo-36871: Improve error handling for the assert_has_calls and
assert_has_awaits methods of mocks. Fixed a bug where any errors
encountered while binding the expected calls to the mock's spec were
silently swallowed, leading to misleading error output.

- bpo-11410: Better control over symbol visibility is provided through use
of the visibility attributes available in gcc >= 4.0, provided in a
uniform way across POSIX and Windows. The POSIX build files have been
updated to compile with -fvisibility=hidden, minimising exported symbols.

- bpo-38219: Optimized the :class:`dict` constructor and the
:meth:`~dict.update` method for the case when the argument is a dict.

- bpo-38236: Python now dumps path configuration if it fails to import the
Python codecs of the filesystem and stdio encodings.

- bpo-38013: Allow to call ``async_generator_athrow().throw(...)`` even for
non-started async generator helper. It fixes annoying warning at the end
of :func:`asyncio.run` call.

- bpo-38124: Fix an off-by-one error in PyState_AddModule that could cause
out-of-bounds memory access.

- bpo-38116: The select module is now PEP-384 compliant and no longer has
static state

- bpo-38113: ast module updated to PEP-384 and all statics removed

- bpo-38076: The struct module is now PEP-384 compatible

- bpo-38075: The random module is now PEP-384 compatible

- bpo-38074: zlib module made PEP-384 compatible

- bpo-38073: Make pwd extension module PEP-384 compatible

- bpo-38072: grp module made PEP-384 compatible

- bpo-38069: Make _posixsubprocess PEP-384 compatible

- bpo-38071: Make termios extension module PEP-384 compatible

- bpo-38005: Fixed comparing and creating of InterpreterID and ChannelID.

- bpo-36946: Fix possible signed integer overflow when handling slices.
Patch by hongweipeng.

- bpo-37994: Fixed silencing arbitrary errors if an attribute lookup fails
in several sites. Only AttributeError should be silenced.

- bpo-8425: Optimize set difference_update for the case when the other set
is much larger than the base set. (Suggested by Evgeny Kapun with code
contributed by Michele Orrù).

- bpo-37966: The implementation of :func:`~unicodedata.is_normalized` has
been greatly sped up on strings that aren't normalized, by implementing
the full normalization-quick-check algorithm from the Unicode standard.

- bpo-37947: Adjust correctly the recursion level in the symtable generation
for named expressions. Patch by Pablo Galindo.

- bpo-37812: The ``CHECK_SMALL_INT`` macro used inside
:file:`Object/longobject.c` has been replaced with an explicit ``return``
at each call site.

- bpo-37751: Fix :func:`codecs.lookup` to normalize the encoding name the
same way than :func:`encodings.normalize_encoding`, except that
:func:`codecs.lookup` also converts the name to lower case.

- bpo-37830: Fixed compilation of :keyword:`break` and :keyword:`continue`
in the :keyword:`finally` block when the corresponding :keyword:`try`
block contains :keyword:`return` with a non-constant value.

- bpo-20490: Improve import error message for partially initialized module
on circular ``from`` imports - by Anthony Sottile.

- bpo-37840: Fix handling of negative indices in
:c:member:`~PySequenceMethods.sq_item` of :class:`bytearray`. Patch by
Sergey Fedoseev.

- bpo-37802: Slightly improve performance of
:c:func:`PyLong_FromUnsignedLong`, :c:func:`PyLong_FromUnsignedLongLong`
and :c:func:`PyLong_FromSize_t`. Patch by Sergey Fedoseev.

- bpo-37409: Ensure explicit relative imports from interactive sessions and
scripts (having no parent package) always raise ImportError, rather than
treating the current module as the package. Patch by Ben Lewis.

- bpo-32912: Reverted :issue:`32912`: emitting :exc:`SyntaxWarning` instead
of :exc:`DeprecationWarning` for invalid escape sequences in string and
bytes literals.

- bpo-37757: :pep:`572`: As described in the PEP, assignment expressions now
raise :exc:`SyntaxError` when their interaction with comprehension scoping
results in an ambiguous target scope.

The ``TargetScopeError`` subclass originally proposed by the PEP has been
removed in favour of just raising regular syntax errors for the disallowed
cases.

- bpo-36279: Fix potential use of uninitialized memory in :func:`os.wait3`.

- bpo-36311: Decoding bytes objects larger than 2GiB is faster and no longer
fails when a multibyte characters spans a chunk boundary.

- bpo-34880: The :keyword:`assert` statement now works properly if the
:exc:`AssertionError` exception is being shadowed. Patch by Zackery Spytz.

- bpo-37340: Removed object cache (``free_list``) for bound method objects.
Temporary bound method objects are less used than before thanks to the
``LOAD_METHOD`` opcode and the ``_PyObject_VectorcallMethod`` C API.

- bpo-37648: Fixed minor inconsistency in :meth:`list.__contains__`,
:meth:`tuple.__contains__` and a few other places. The collection's item
is now always at the left and the needle is on the right of ``==``.

- bpo-37444: Update differing exception between :meth:`builtins.__import__`
and :meth:`importlib.__import__`.

- bpo-37619: When adding a wrapper descriptor from one class to a different
class (for example, setting ``__add__ = str.__add__`` on an ``int``
subclass), an exception is correctly raised when the operator is called.

- bpo-37593: Swap the positions of the *posonlyargs* and *args* parameters
in the constructor of :class:`ast.parameters` nodes.

- bpo-37543: Optimized pymalloc for non PGO build.

- bpo-37537: Compute allocated pymalloc blocks inside
_Py_GetAllocatedBlocks(). This slows down _Py_GetAllocatedBlocks() but
gives a small speedup to _PyObject_Malloc() and _PyObject_Free().

- bpo-37467: Fix :func:`sys.excepthook` and :c:func:`PyErr_Display` if a
filename is a bytes string. For example, for a SyntaxError exception where
the filename attribute is a bytes string.

- bpo-37433: Fix ``SyntaxError`` indicator printing too many spaces for
multi-line strings - by Anthony Sottile.

- bpo-37417: :meth:`bytearray.extend` now correctly handles errors that
arise during iteration. Patch by Brandt Bucher.

- bpo-37414: The undocumented ``sys.callstats()`` function has been removed.
Since Python 3.7, it was deprecated and always returned ``None``. It
required a special build option ``CALL_PROFILE`` which was already removed
in Python 3.7.

- bpo-37392: Remove ``sys.getcheckinterval()`` and
``sys.setcheckinterval()`` functions. They were deprecated since Python
3.2. Use :func:`sys.getswitchinterval` and :func:`sys.setswitchinterval`
instead. Remove also ``check_interval`` field of the
``PyInterpreterState`` structure.

- bpo-37388: In development mode and in debug build, *encoding* and *errors*
arguments are now checked on string encoding and decoding operations.
Examples: :func:`open`, :meth:`str.encode` and :meth:`bytes.decode`.

By default, for best performances, the *errors* argument is only checked
at the first encoding/decoding error, and the *encoding* argument is
sometimes ignored for empty strings.

- bpo-37348: Optimized decoding short ASCII string with UTF-8 and ascii
codecs. ``b"foo".decode()`` is about 15% faster. Patch by Inada Naoki.

- bpo-24214: Improved support of the surrogatepass error handler in the
UTF-8 and UTF-16 incremental decoders.

- bpo-35224: Reverse evaluation order of key: value in dict comprehensions
as proposed in PEP 572. I.e. in ``{k: v for ...}``, ``k`` will be
evaluated before ``v``.

- bpo-37316: Fix the :c:func:`PySys_Audit` call in :class:`mmap.mmap`.

- bpo-37300: Remove an unnecessary Py_XINCREF in classobject.c.

- bpo-37269: Fix a bug in the peephole optimizer that was not treating
correctly constant conditions with binary operators. Patch by Pablo
Galindo.

- bpo-20443: Python now gets the absolute path of the script filename
specified on the command line (ex: "python3 script.py"): the __file__
attribute of the __main__ module and sys.path[0] become an absolute path,
rather than a relative path.

- bpo-37257: Python's small object allocator (``obmalloc.c``) now allows (no
more than) one empty arena to remain available for immediate reuse,
without returning it to the OS. This prevents thrashing in simple loops
where an arena could be created and destroyed anew on each iteration.

- bpo-37231: The dispatching of type slots to special methods (for example
calling ``__mul__`` when doing ``x * y``) has been made faster.

- bpo-36974: Implemented separate vectorcall functions for every calling
convention of builtin functions and methods. This improves performance for
calls.

- bpo-37213: Handle correctly negative line offsets in the peephole
optimizer. Patch by Pablo Galindo.

- bpo-37219: Remove erroneous optimization for empty set differences.

- bpo-15913: Implement :c:func:`PyBuffer_SizeFromFormat()` function
(previously documented but not implemented): call :func:`struct.calcsize`.
Patch by Joannah Nanjekye.

- bpo-36922: Slot functions optimize any callable with
``Py_TPFLAGS_METHOD_DESCRIPTOR`` instead of only instances of
``function``.

- bpo-36974: The slot ``tp_vectorcall_offset`` is inherited unconditionally
to support ``super().__call__()`` when the base class uses vectorcall.

- bpo-37160: :func:`threading.get_native_id` now also supports NetBSD.

- bpo-37077: Add :func:`threading.get_native_id` support for AIX. Patch by
M. Felt

- bpo-36781: :func:`sum` has been optimized for boolean values.

- bpo-34556: Add ``--upgrade-deps`` to venv module. Patch by Cooper Ry Lees

- bpo-20523: ``pdb.Pdb`` supports ~/.pdbrc in Windows 7. Patch by Tim Hopper
and Dan Lidral-Porter.

- bpo-35551: Updated encodings: - Removed the "tis260" encoding, which was
an alias for the nonexistent "tactis" codec. - Added "mac_centeuro" as an
alias for the mac_latin2 encoding.

- bpo-19072: The :class:`classmethod` decorator can now wrap other
descriptors such as property objects. Adapted from a patch written by
Graham Dumpleton.

- bpo-27575: Improve speed of dictview intersection by directly using set
intersection logic. Patch by David Su.

- bpo-30773: Prohibit parallel running of aclose() / asend() / athrow(). Fix
ag_running to reflect the actual running status of the AG.

Library
-------

- bpo-36589: The :func:`curses.update_lines_cols` function now returns
``None`` instead of ``1`` on success.

- bpo-38807: Update :exc:`TypeError` messages for :meth:`os.path.join` to
include :class:`os.PathLike` objects as acceptable input types.

- bpo-38724: Add a repr for ``subprocess.Popen`` objects. Patch by Andrey
Doroschenko.

- bpo-38786: pydoc now recognizes and parses HTTPS URLs. Patch by python273.

- bpo-38785: Prevent asyncio from crashing if parent ``__init__`` is not
called from a constructor of object derived from ``asyncio.Future``.

- bpo-38723: :mod:`pdb` now uses :meth:`io.open_code` to trigger auditing
events.

- bpo-27805: Allow opening pipes and other non-seekable files in append mode
with :func:`open`.

- bpo-38438: Simplify the :mod:`argparse` usage message for ``nargs="*"``.

- bpo-38761: WeakSet is now registered as a collections.abc.MutableSet.

- bpo-38716: logging: change RotatingHandler namer and rotator to
class-level attributes. This stops __init__ from setting them to None in
the case where a subclass defines them with eponymous methods.

- bpo-38713: Add :data:`os.P_PIDFD` constant, which may be passed to
:func:`os.waitid` to wait on a Linux process file descriptor.

- bpo-38692: Add :class:`asyncio.PidfdChildWatcher`, a Linux-specific child
watcher implementation that polls process file descriptors.

- bpo-38692: Expose the Linux ``pidfd_open`` syscall as
:func:`os.pidfd_open`.

- bpo-38602: Added constants :data:`~fcntl.F_OFD_GETLK`,
:data:`~fcntl.F_OFD_SETLK` and :data:`~fcntl.F_OFD_SETLKW` to the
:mod:`fcntl` module. Patch by Dong-hee Na.

- bpo-38334: Fixed seeking backward on an encrypted
:class:`zipfile.ZipExtFile`.

- bpo-38312: Add :func:`curses.get_escdelay`, :func:`curses.set_escdelay`,
:func:`curses.get_tabsize`, and :func:`curses.set_tabsize` functions - by
Anthony Sottile.

- bpo-38586: Now :func:`~logging.config.fileConfig` correctly sets the .name
of handlers loaded.

- bpo-38565: Add new cache_parameters() method for functools.lru_cache() to
better support pickling.

- bpo-34679: asynci.ProactorEventLoop.close() now only calls
signal.set_wakeup_fd() in the main thread.

- bpo-31202: The case the result of :func:`pathlib.WindowsPath.glob` matches
now the case of the pattern for literal parts.

- bpo-36321: Remove misspelled attribute. The 3.8 changelog noted that this
would be removed in 3.9.

- bpo-38521: Fixed erroneous equality comparison in statistics.NormalDist().

- bpo-38493: Added :data:`~os.CLD_KILLED` and :data:`~os.CLD_STOPPED` for
:attr:`si_code`. Patch by Dong-hee Na.

- bpo-38478: Fixed a bug in :meth:`inspect.signature.bind` that was causing
it to fail when handling a keyword argument with same name as
positional-only parameter. Patch by Pablo Galindo.

- bpo-33604: Fixed `hmac.new` and `hmac.HMAC` to raise TypeError instead of
ValueError when the digestmod parameter, now required in 3.8, is omitted.
Also clarified the hmac module documentation and docstrings.

- bpo-38378: Parameters *out* and *in* of :func:`os.sendfile` was renamed to
*out_fd* and *in_fd*.

- bpo-38417: Added support for setting the umask in the child process to the
subprocess module on POSIX systems.

- bpo-38449: Revert PR 15522, which introduces a regression in
:meth:`mimetypes.guess_type` due to improper handling of filenames as
urls.

- bpo-38431: Fix ``__repr__`` method for :class:`dataclasses.InitVar` to
support typing objects, patch by Samuel Colvin.

- bpo-38109: Add missing :data:`stat.S_IFDOOR`, :data:`stat.S_IFPORT`,
:data:`stat.S_IFWHT`, :func:`stat.S_ISDOOR`, :func:`stat.S_ISPORT`, and
:func:`stat.S_ISWHT` values to the Python implementation of :mod:`stat`.

- bpo-38422: Clarify docstrings of pathlib suffix(es)

- bpo-38405: Nested subclasses of :class:`typing.NamedTuple` are now
pickleable.

- bpo-38332: Prevent :exc:`KeyError` thrown by :func:`_encoded_words.decode`
when given an encoded-word with invalid content-type encoding from
propagating all the way to :func:`email.message.get`.

- bpo-38371: Deprecated the ``split()`` method in
:class:`_tkinter.TkappType` in favour of the ``splitlist()`` method which
has more consistent and predicable behavior.

- bpo-38341: Add :exc:`smtplib.SMTPNotSupportedError` to the :mod:`smtplib`
exported names.

- bpo-38319: sendfile() used in socket and shutil modules was raising
OverflowError for files >= 2GiB on 32-bit architectures. (patch by
Giampaolo Rodola)

- bpo-38242: Revert the new asyncio Streams API

- bpo-13153: OS native encoding is now used for converting between Python
strings and Tcl objects. This allows to display, copy and paste to
clipboard emoji and other non-BMP characters. Converting strings from Tcl
to Python and back now never fails (except MemoryError).

- bpo-38019: Correctly handle pause/resume reading of closed asyncio unix
pipe.

- bpo-38163: Child mocks will now detect their type as either synchronous or
asynchronous, asynchronous child mocks will be AsyncMocks and synchronous
child mocks will be either MagicMock or Mock (depending on their parent
type).

- bpo-38161: Removes _AwaitEvent from AsyncMock.

- bpo-38216: Allow the rare code that wants to send invalid http requests
from the `http.client` library a way to do so. The fixes for bpo-30458
led to breakage for some projects that were relying on this ability to
test their own behavior in the face of bad requests.

- bpo-28286: Deprecate opening :class:`~gzip.GzipFile` for writing
implicitly. Always specify the *mode* argument for writing.

- bpo-38108: Any synchronous magic methods on an AsyncMock now return a
MagicMock. Any asynchronous magic methods on a MagicMock now return an
AsyncMock.

- bpo-38265: Update the *length* parameter of :func:`os.pread` to accept
:c:type:`Py_ssize_t` instead of :c:expr:`int`.

- bpo-38112: :mod:`compileall` has a higher default recursion limit and new
command-line arguments for path manipulation, symlinks handling, and
multiple optimization levels.

- bpo-38248: asyncio: Fix inconsistent immediate Task cancellation

- bpo-38237: The arguments for the builtin pow function are more
descriptive. They can now also be passed in as keywords.

- bpo-34002: Improve efficiency in parts of email package by changing
while-pop to a for loop, using isdisjoint instead of set intersections.

- bpo-38191: Constructors of :class:`~typing.NamedTuple` and
:class:`~typing.TypedDict` types now accept arbitrary keyword argument
names, including "cls", "self", "typename", "_typename", "fields" and
"_fields".

- bpo-38155: Add ``__all__`` to :mod:`datetime`. Patch by Tahia Khan.

- bpo-38185: Fixed case-insensitive string comparison in
:class:`sqlite3.Row` indexing.

- bpo-38136: Changes AsyncMock call count and await count to be two
different counters. Now await count only counts when a coroutine has been
awaited, not when it has been called, and vice-versa. Update the
documentation around this.

- bpo-37828: Fix default mock name in
:meth:`unittest.mock.Mock.assert_called` exceptions. Patch by Abraham
Toriz Cruz.

- bpo-38175: Fix a memory leak in comparison of :class:`sqlite3.Row`
objects.

- bpo-33936: _hashlib no longer calls obsolete OpenSSL initialization
function with OpenSSL 1.1.0+.

- bpo-34706: Preserve subclassing in inspect.Signature.from_callable.

- bpo-38153: Names of hashing algorithms from OpenSSL are now normalized to
follow Python's naming conventions. For example OpenSSL uses sha3-512
instead of sha3_512 or blake2b512 instead of blake2b.

- bpo-38115: Fix a bug in dis.findlinestarts() where it would return invalid
bytecode offsets. Document that a code object's co_lnotab can contain
invalid bytecode offsets.

- bpo-38148: Add slots to :mod:`asyncio` transport classes, which can reduce
memory usage.

- bpo-38142: The _hashlib OpenSSL wrapper extension module is now PEP-384
compliant.

- bpo-9216: hashlib constructors now support usedforsecurity flag to signal
that a hashing algorithm is not used in a security context.

- bpo-36991: Fixes a potential incorrect AttributeError exception escaping
ZipFile.extract() in some unsupported input error situations.

- bpo-38134: Remove obsolete copy of PBKDF2_HMAC_fast. All supported OpenSSL
versions contain a fast implementation.

- bpo-38132: The OpenSSL hashlib wrapper uses a simpler implementation.
Several Macros and pointless caches are gone. The hash name now comes from
OpenSSL's EVP. The algorithm name stays the same, except it is now always
lower case.

- bpo-38008: Fix parent class check in protocols to correctly identify the
module that provides a builtin protocol, instead of assuming they all come
from the :mod:`collections.abc` module

- bpo-34037: For :mod:`asyncio`, add a new coroutine
:meth:`loop.shutdown_default_executor`. The new coroutine provides an API
to schedule an executor shutdown that waits on the threadpool to finish
closing. Also, :func:`asyncio.run` has been updated to utilize the new
coroutine. Patch by Kyle Stanley.

- bpo-37405: Fixed regression bug for socket.getsockname() for non-CAN_ISOTP
AF_CAN address family sockets by returning a 1-tuple instead of string.

- bpo-38121: Update parameter names on functions in importlib.metadata
matching the changes in the 0.22 release of importlib_metadata.

- bpo-38110: The os.closewalk() implementation now uses the libc fdwalk()
API on platforms where it is available.

- bpo-38093: Fixes AsyncMock so it doesn't crash when used with
AsyncContextManagers or AsyncIterators.

- bpo-37488: Add warning to :meth:`datetime.utctimetuple`,
:meth:`datetime.utcnow` and :meth:`datetime.utcfromtimestamp` .

- bpo-35640: Allow passing a :term:`path-like object` as ``directory``
argument to the :class:`http.server.SimpleHTTPRequestHandler` class. Patch
by Géry Ogam.

- bpo-38086: Update importlib.metadata with changes from `importlib_metadata
0.21
<https://gitlab.com/python-devs/importlib_metadata/blob/0.21/importlib_metadata/docs/changelog.rst>`_.

- bpo-37251: Remove `__code__` check in AsyncMock that incorrectly evaluated
function specs as async objects but failed to evaluate classes with
`__await__` but no `__code__` attribute defined as async objects.

- bpo-38037: Fix reference counters in the :mod:`signal` module.

- bpo-38066: Hide internal asyncio.Stream methods: feed_eof(), feed_data(),
set_exception() and set_transport().

- bpo-38059: inspect.py now uses sys.exit() instead of exit()

- bpo-38049: Added command-line interface for the :mod:`ast` module.

- bpo-37953: In :mod:`typing`, improved the ``__hash__`` and ``__eq__``
methods for :class:`ForwardReferences`.

- bpo-38026: Fixed :func:`inspect.getattr_static` used ``isinstance`` while
it should avoid dynamic lookup.

- bpo-35923: Update :class:`importlib.machinery.BuiltinImporter` to use
``loader._ORIGIN`` instead of a hardcoded value. Patch by Dong-hee Na.

- bpo-38010: In ``importlib.metadata`` sync with ``importlib_metadata``
0.20, clarifying behavior of ``files()`` and fixing issue where only one
requirement was returned for ``requires()`` on ``dist-info`` packages.

- bpo-38006: weakref.WeakValueDictionary defines a local remove() function
used as callback for weak references. This function was created with a
closure. Modify the implementation to avoid the closure.

- bpo-37995: Added the *indent* option to :func:`ast.dump` which allows it
to produce a multiline indented output.

- bpo-34410: Fixed a crash in the :func:`tee` iterator when re-enter it.
RuntimeError is now raised in this case.

- bpo-37140: Fix a ctypes regression of Python 3.8. When a ctypes.Structure
is passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be called
exactly once. Fix ctypes internals to no longer call the finalizer twice.

- bpo-37587: ``_json.scanstring`` is now up to 3x faster when there are many
backslash escaped characters in the JSON string.

- bpo-37834: Prevent shutil.rmtree exception when built on non-Windows
system without fd system call support, like older versions of macOS.

- bpo-10978: Semaphores and BoundedSemaphores can now release more than one
waiting thread at a time.

- bpo-37972: Subscripts to the `unittest.mock.call` objects now receive the
same chaining mechanism as any other custom attributes, so that the
following usage no longer raises a `TypeError`:

call().foo().__getitem__('bar')

Patch by blhsing

- bpo-37965: Fix C compiler warning caused by
distutils.ccompiler.CCompiler.has_function.

- bpo-37964: Add ``F_GETPATH`` command to :mod:`fcntl`.

- bpo-37960: ``repr()`` of buffered and text streams now silences only
expected exceptions when get the value of "name" and "mode" attributes.

- bpo-37961: Add a ``total_nframe`` field to the traces collected by the
tracemalloc module. This field indicates the original number of frames
before it was truncated.

- bpo-37951: Most features of the subprocess module now work again in
subinterpreters. Only *preexec_fn* is restricted in subinterpreters.

- bpo-36205: Fix the rusage implementation of time.process_time() to
correctly report the sum of the system and user CPU time.

- bpo-37950: Fix :func:`ast.dump` when call with incompletely initialized
node.

- bpo-34679: Restores instantiation of Windows IOCP event loops from the
non-main thread.

- bpo-36917: Add default implementation of the
:meth:`ast.NodeVisitor.visit_Constant` method which emits a deprecation
warning and calls corresponding methody ``visit_Num()``, ``visit_Str()``,
etc.

- bpo-37798: Update test_statistics.py to verify that the statistics module
works well for both C and Python implementations. Patch by Dong-hee Na

- bpo-26589: Added a new status code to the http module: 451
UNAVAILABLE_FOR_LEGAL_REASONS

- bpo-37915: Fix a segmentation fault that appeared when comparing instances
of ``datetime.timezone`` and ``datetime.tzinfo`` objects. Patch by Pablo
Galindo.

- bpo-32554: Deprecate having random.seed() call hash on arbitrary types.

- bpo-9938: Add optional keyword argument ``exit_on_error`` for
:class:`ArgumentParser`.

- bpo-37851: The :mod:`faulthandler` module no longer allocates its
alternative stack at Python startup. Now the stack is only allocated at
the first faulthandler usage.

- bpo-32793: Fix a duplicated debug message when
:meth:`smtplib.SMTP.connect` is called.

- bpo-37885: venv: Don't generate unset variable warning on deactivate.

- bpo-37868: Fix dataclasses.is_dataclass when given an instance that never
raises AttributeError in __getattr__. That is, an object that returns
something for __dataclass_fields__ even if it's not a dataclass.

- bpo-37811: Fix ``socket`` module's ``socket.connect(address)`` function
being unable to establish connection in case of interrupted system call.
The problem was observed on all OSes which ``poll(2)`` system call can
take only non-negative integers and -1 as a timeout value.

- bpo-37863: Optimizations for Fraction.__hash__ suggested by Tim Peters.

- bpo-21131: Fix ``faulthandler.register(chain=True)`` stack. faulthandler
now allocates a dedicated stack of ``SIGSTKSZ*2`` bytes, instead of just
``SIGSTKSZ`` bytes. Calling the previous signal handler in faulthandler
signal handler uses more than ``SIGSTKSZ`` bytes of stack memory on some
platforms.

- bpo-37798: Add C fastpath for statistics.NormalDist.inv_cdf() Patch by
Dong-hee Na

- bpo-37804: Remove the deprecated method `threading.Thread.isAlive()`.
Patch by Dong-hee Na.

- bpo-37819: Add Fraction.as_integer_ratio() to match the corresponding
methods in bool, int, float, and decimal.

- bpo-14465: Add an xml.etree.ElementTree.indent() function for
pretty-printing XML trees. Contributed by Stefan Behnel.

- bpo-37810: Fix :mod:`difflib` ``?`` hint in diff output when dealing with
tabs. Patch by Anthony Sottile.

- bpo-37772: In ``zipfile.Path``, when adding implicit dirs, ensure that
ancestral directories are added and that duplicates are excluded.

- bpo-18578: Renamed and documented `test.bytecode_helper` as
`test.support.bytecode_helper`. Patch by Joannah Nanjekye.

- bpo-37785: Fix xgettext warnings in :mod:`argparse`.

- bpo-34488: :meth:`writelines` method of :class:`io.BytesIO` is now
slightly faster when many small lines are passed. Patch by Sergey
Fedoseev.

- bpo-37449: `ensurepip` now uses `importlib.resources.read_binary()` to
read data instead of `pkgutil.get_data()`. Patch by Joannah Nanjekye.

- bpo-28292: Mark calendar.py helper functions as being private. The
follows PEP 8 guidance to maintain the style conventions in the module and
it addresses a known case of user confusion.

- bpo-18049: Add definition of THREAD_STACK_SIZE for AIX in
Python/thread_pthread.h The default thread stacksize caused crashes with
the default recursion limit Patch by M Felt

- bpo-37742: The logging.getLogger() API now returns the root logger when
passed the name 'root', whereas previously it returned a non-root logger
named 'root'. This could affect cases where user code explicitly wants a
non-root logger named 'root', or instantiates a logger using
logging.getLogger(__name__) in some top-level module called 'root.py'.

- bpo-37738: Fix the implementation of curses ``addch(str, color_pair)``:
pass the color pair to ``setcchar()``, instead of always passing 0 as the
color pair.

- bpo-37723: Fix performance regression on regular expression parsing with
huge character sets. Patch by Yann Vaginay.

- bpo-35943: The function :c:func:`PyImport_GetModule` now ensures any
module it returns is fully initialized. Patch by Joannah Nanjekye.

- bpo-32178: Fix IndexError in :mod:`email` package when trying to parse
invalid address fields starting with ``:``.

- bpo-37268: The :mod:`parser` module is deprecated and will be removed in
future versions of Python.

- bpo-11953: Completing WSA* error codes in :mod:`socket`.

- bpo-37685: Fixed comparisons of :class:`datetime.timedelta` and
:class:`datetime.timezone`.

- bpo-37697: Synchronize ``importlib.metadata`` with `importlib_metadata
0.19
<https://gitlab.com/python-devs/importlib_metadata/-/milestones/20>`_,
improving handling of EGG-INFO files and fixing a crash when entry point
names contained colons.

- bpo-37695: Correct :func:`curses.unget_wch` error message. Patch by
Anthony Sottile.

- bpo-37689: Add :meth:`is_relative_to` in :class:`PurePath` to determine
whether or not one path is relative to another.

- bpo-29553: Fixed :meth:`argparse.ArgumentParser.format_usage` for mutually
exclusive groups. Patch by Andrew Nester.

- bpo-37691: Let math.dist() accept coordinates as sequences (or iterables)
rather than just tuples.

- bpo-37685: Fixed ``__eq__``, ``__lt__`` etc implementations in some
classes. They now return :data:`NotImplemented` for unsupported type of
the other operand. This allows the other operand to play role (for example
the equality comparison with :data:`~unittest.mock.ANY` will return
``True``).

- bpo-37354: Make Activate.ps1 Powershell script static to allow for signing
it.

- bpo-37664: Update wheels bundled with ensurepip (pip 19.2.3 and setuptools
41.2.0)

- bpo-37663: Bring consistency to venv shell activation scripts by always
using __VENV_PROMPT__.

- bpo-37642: Allowed the pure Python implementation of
:class:`datetime.timezone` to represent sub-minute offsets close to
minimum and maximum boundaries, specifically in the ranges (23:59, 24:00)
and (-23:59, 24:00). Patch by Ngalim Siregar

- bpo-36161: In :mod:`posix`, use ``ttyname_r`` instead of ``ttyname`` for
thread safety.

- bpo-36324: Make internal attributes for statistics.NormalDist() private.

- bpo-37555: Fix `NonCallableMock._call_matcher` returning tuple instead of
`_Call` object when `self._spec_signature` exists. Patch by Elizabeth
Uselton

- bpo-29446: Make `from tkinter import *` import only the expected objects.

- bpo-16970: Adding a value error when an invalid value in passed to nargs
Patch by Robert Leenders

- bpo-34443: Exceptions from :mod:`enum` now use the ``__qualname`` of the
enum class in the exception message instead of the ``__name__``.

- bpo-37491: Fix ``IndexError`` when parsing email headers with unexpectedly
ending bare-quoted string value. Patch by Abhilash Raj.

- bpo-37587: Make json.loads faster for long strings. (Patch by Marco
Paolini)

- bpo-18378: Recognize "UTF-8" as a valid value for LC_CTYPE in
locale._parse_localename.

- bpo-37579: Return :exc:`NotImplemented` in Python implementation of
``__eq__`` for :class:`~datetime.timedelta` and :class:`~datetime.time`
when the other object being compared is not of the same type to match C
implementation. Patch by Karthikeyan Singaravelan.

- bpo-21478: Record calls to parent when autospecced object is attached to a
mock using :func:`unittest.mock.attach_mock`. Patch by Karthikeyan
Singaravelan.

- bpo-37531: "python3 -m test -jN --timeout=TIMEOUT" now kills a worker
process if it runs longer than *TIMEOUT* seconds.

- bpo-37482: Fix serialization of display name in originator or destination
address fields with both encoded words and special chars.

- bpo-36993: Improve error reporting for corrupt zip files with bad zip64
extra data. Patch by Daniel Hillier.

- bpo-37502: pickle.loads() no longer raises TypeError when the buffers
argument is set to None

- bpo-37520: Correct behavior for zipfile.Path.parent when the path object
identifies a subdirectory.

- bpo-18374: Fix the ``.col_offset`` attribute of nested :class:`ast.BinOp`
instances which had a too large value in some situations.

- bpo-37424: Fixes a possible hang when using a timeout on
`subprocess.run()` while capturing output. If the child process spawned
its own children or otherwise connected its stdout or stderr handles with
another process, we could hang after the timeout was reached and our child
was killed when attempting to read final output from the pipes.

- bpo-37421: Fix :func:`multiprocessing.util.get_temp_dir` finalizer: clear
also the 'tempdir' configuration of the current process, so next call to
``get_temp_dir()`` will create a new temporary directory, rather than
reusing the removed temporary directory.

- bpo-37481: The distutils ``bdist_wininst`` command is deprecated in Python
3.8, use ``bdist_wheel`` (wheel packages) instead.

- bpo-37479: When `Enum.__str__` is overridden in a derived class, the
override will be used by `Enum.__format__` regardless of whether mixin
classes are present.

- bpo-37440: http.client now enables TLS 1.3 post-handshake authentication
for default context or if a cert_file is passed to HTTPSConnection.

- bpo-37437: Update vendorized expat version to 2.2.7.

- bpo-37428: SSLContext.post_handshake_auth = True no longer sets
SSL_VERIFY_POST_HANDSHAKE verify flag for client connections. Although the
option is documented as ignored for clients, OpenSSL implicitly enables
cert chain validation when the flag is set.

- bpo-37420: :func:`os.sched_setaffinity` now correctly handles errors that
arise during iteration over its ``mask`` argument. Patch by Brandt Bucher.

- bpo-37412: The :func:`os.getcwdb` function now uses the UTF-8 encoding on
Windows, rather than the ANSI code page: see :pep:`529` for the rationale.
The function is no longer deprecated on Windows.

- bpo-37406: The sqlite3 module now raises TypeError, rather than
ValueError, if operation argument type is not str: execute(),
executemany() and calling a connection.

- bpo-29412: Fix IndexError in parsing a header value ending unexpectedly.
Patch by Abhilash Raj.

- bpo-36546: The *dist* argument for statistics.quantiles() is now
positional only. The current name doesn't reflect that the argument can be
either a dataset or a distribution. Marking the parameter as positional
avoids confusion and makes it possible to change the name later.

- bpo-37394: Fix a bug that was causing the :mod:`queue` module to fail if
the accelerator module was not available. Patch by Pablo Galindo.

- bpo-37376: :mod:`pprint` now has support for
:class:`types.SimpleNamespace`. Patch by Carl Bordum Hansen.

- bpo-26967: An :class:`~argparse.ArgumentParser` with
``allow_abbrev=False`` no longer disables grouping of short flags, such as
``-vv``, but only disables abbreviation of long flags as documented. Patch
by Zac Hatfield-Dodds.

- bpo-37212: :func:`unittest.mock.call` now preserves the order of keyword
arguments in repr output. Patch by Karthikeyan Singaravelan.

- bpo-37372: Fix error unpickling datetime.time objects from Python 2 with
seconds>=24. Patch by Justin Blanchard.

- bpo-37345: Add formal support for UDPLITE sockets. Support was present
before, but it is now easier to detect support with ``hasattr(socket,
'IPPROTO_UDPLITE')`` and there are constants defined for each of the
values needed: :py:obj:`socket.IPPROTO_UDPLITE`,
:py:obj:`UDPLITE_SEND_CSCOV`, and :py:obj:`UDPLITE_RECV_CSCOV`. Patch by
Gabe Appleton.

- bpo-37358: Optimized ``functools.partial`` by using vectorcall.

- bpo-37347: :meth:`sqlite3.Connection.create_aggregate`,
:meth:`sqlite3.Connection.create_function`,
:meth:`sqlite3.Connection.set_authorizer`,
:meth:`sqlite3.Connection.set_progress_handler`
:meth:`sqlite3.Connection.set_trace_callback` methods lead to segfaults if
some of these methods are called twice with an equal object but not the
same. Now callbacks are stored more carefully. Patch by Aleksandr Balezin.

- bpo-37163: The *obj* argument of :func:`dataclasses.replace` is
positional-only now.

- bpo-37085: Add the optional Linux SocketCAN Broadcast Manager constants,
used as flags to configure the BCM behaviour, in the socket module. Patch
by Karl Ding.

- bpo-37328: ``HTMLParser.unescape`` is removed. It was undocumented and
deprecated since Python 3.4.

- bpo-37305: Add .webmanifest -> application/manifest+json to list of
recognized file types and content type headers

- bpo-37320: ``aifc.openfp()`` alias to ``aifc.open()``, ``sunau.openfp()``
alias to ``sunau.open()``, and ``wave.openfp()`` alias to ``wave.open()``
have been removed. They were deprecated since Python 3.7.

- bpo-37315: Deprecated accepting floats with integral value (like ``5.0``)
in :func:`math.factorial`.

- bpo-37312: ``_dummy_thread`` and ``dummy_threading`` modules have been
removed. These modules were deprecated since Python 3.7 which requires
threading support.

- bpo-33972: Email with single part but content-type set to ``multipart/*``
doesn't raise AttributeError anymore.

- bpo-37280: Use threadpool for reading from file for sendfile fallback
mode.

- bpo-37279: Fix asyncio sendfile support when sendfile sends extra data in
fallback mode.

- bpo-19865: :func:`ctypes.create_unicode_buffer()` now also supports
non-BMP characters on platforms with 16-bit :c:type:`wchar_t` (for
example, Windows and AIX).

- bpo-37266: In a subinterpreter, spawning a daemon thread now raises an
exception. Daemon threads were never supported in subinterpreters.
Previously, the subinterpreter finalization crashed with a Python fatal
error if a daemon thread was still running.

- bpo-37210: Allow pure Python implementation of :mod:`pickle` to work even
when the C :mod:`_pickle` module is unavailable.

- bpo-21872: Fix :mod:`lzma`: module decompresses data incompletely. When
decompressing a FORMAT_ALONE format file, and it doesn't have the end
marker, sometimes the last one to dozens bytes can't be output. Patch by
Ma Lin.

- bpo-35922: Fix :meth:`RobotFileParser.crawl_delay` and
:meth:`RobotFileParser.request_rate` to return ``None`` rather than raise
:exc:`AttributeError` when no relevant rule is defined in the robots.txt
file. Patch by Rémi Lapeyre.

- bpo-35766: Change the format of feature_version to be a (major, minor)
tuple.

- bpo-36607: Eliminate :exc:`RuntimeError` raised by
:func:`asyncio.all_tasks()` if internal tasks weak set is changed by
another thread during iteration.

- bpo-18748: :class:`_pyio.IOBase` destructor now does nothing if getting
the ``closed`` attribute fails to better mimic :class:`_io.IOBase`
finalizer.

- bpo-36402: Fix a race condition at Python shutdown when waiting for
threads. Wait until the Python thread state of all non-daemon threads get
deleted (join all non-daemon threads), rather than just wait until
non-daemon Python threads complete.

- bpo-37206: Default values which cannot be represented as Python objects no
longer improperly represented as ``None`` in function signatures.

- bpo-37111: Added ``encoding`` and ``errors`` keyword parameters to
``logging.basicConfig``.

- bpo-12144: Ensure cookies with ``expires`` attribute are handled in
:meth:`CookieJar.make_cookies`.

- bpo-34886: Fix an unintended ValueError from :func:`subprocess.run` when
checking for conflicting `input` and `stdin` or `capture_output` and
`stdout` or `stderr` args when they were explicitly provided but with
`None` values within a passed in `**kwargs` dict rather than as passed
directly by name. Patch contributed by Rémi Lapeyre.

- bpo-37173: The exception message for ``inspect.getfile()`` now correctly
reports the passed class rather than the builtins module.

- bpo-37178: Give math.perm() a one argument form that means the same as
math.factorial().

- bpo-37178: For math.perm(n, k), let k default to n, giving the same result
as factorial.

- bpo-37165: Converted _collections._count_elements to use the Argument
Clinic.

- bpo-34767: Do not always create a :class:`collections.deque` in
:class:`asyncio.Lock`.

- bpo-37158: Speed-up statistics.fmean() by switching from a function to a
generator.

- bpo-34282: Remove ``Enum._convert`` method, deprecated in 3.8.

- bpo-37150: `argparse._ActionsContainer.add_argument` now throws error, if
someone accidentally pass FileType class object instead of instance of
FileType as `type` argument

- bpo-28724: The socket module now has the :func:`socket.send_fds` and
:func:`socket.recv.fds` methods. Contributed by Joannah Nanjekye, Shinya
Okano and Victor Stinner.

- bpo-35621: Support running asyncio subprocesses when execution event loop
in a thread on UNIX.

- bpo-36520: Lengthy email headers with UTF-8 characters are now properly
encoded when they are folded. Patch by Jeffrey Kintscher.

- bpo-30835: Fixed a bug in email parsing where a message with invalid bytes
in content-transfer-encoding of a multipart message can cause an
AttributeError. Patch by Andrew Donnellan.

- bpo-31163: pathlib.Path instance's rename and replace methods now return
the new Path instance.

- bpo-25068: :class:`urllib.request.ProxyHandler` now lowercases the keys of
the passed dictionary.

- bpo-26185: Fix :func:`repr` on empty :class:`ZipInfo` object. Patch by
Mickaël Schoentgen.

- bpo-21315: Email headers containing RFC2047 encoded words are parsed
despite the missing whitespace, and a defect registered. Also missing
trailing whitespace after encoded words is now registered as a defect.

- bpo-31904: Port test_datetime to VxWorks: skip zoneinfo tests on VxWorks

- bpo-35805: Add parser for Message-ID header and add it to default
HeaderRegistry. This should prevent folding of Message-ID using RFC 2048
encoded words.

- bpo-36871: Ensure method signature is used instead of constructor
signature of a class while asserting mock object against method calls.
Patch by Karthikeyan Singaravelan.

- bpo-35070: posix.getgrouplist() now works correctly when the user belongs
to NGROUPS_MAX supplemental groups. Patch by Jeffrey Kintscher.

- bpo-31783: Fix race condition in ThreadPoolExecutor when worker threads
are created during interpreter shutdown.

- bpo-36582: Fix ``UserString.encode()`` to correctly return ``bytes``
rather than a ``UserString`` instance.

- bpo-32424: Deprecate xml.etree.ElementTree.Element.copy() in favor of
copy.copy().

Patch by Gordon P. Hemsley

- bpo-36564: Fix infinite loop in email header folding logic that would be
triggered when an email policy's max_line_length is not long enough to
include the required markup and any values in the message. Patch by Paul
Ganssle

- bpo-36543: Removed methods Element.getchildren(), Element.getiterator()
and ElementTree.getiterator() and the xml.etree.cElementTree module.

- bpo-36409: Remove the old plistlib API deprecated in Python 3.4

- bpo-36302: distutils sorts source file lists so that Extension .so files
build more reproducibly by default

- bpo-36250: Ignore ``ValueError`` from ``signal`` with ``interaction`` in
non-main thread.

- bpo-36046: Added ``user``, ``group`` and ``extra_groups`` parameters to
the subprocess.Popen constructor. Patch by Patrick McLean.

- bpo-32627: Fix compile error when ``_uuid`` headers conflicting included.

- bpo-35800: Deprecate ``smtpd.MailmanProxy`` ready for future removal.

- bpo-35168: :attr:`shlex.shlex.punctuation_chars` is now a read-only
property.

- bpo-8538: Add support for boolean actions like ``--foo`` and ``--no-foo``
to argparse. Patch contributed by Rémi Lapeyre.

- bpo-20504: Fixes a bug in :mod:`cgi` module when a multipart/form-data
request has no `Content-Length` header.

- bpo-25988: The abstract base classes in :mod:`collections.abc` no longer
are exposed in the regular :mod:`collections` module.

- bpo-11122: Distutils won't check for rpmbuild in specified paths only.

- bpo-34775: Division handling of PurePath now returns NotImplemented
instead of raising a TypeError when passed something other than an
instance of str or PurePath. Patch by Roger Aiudi.

- bpo-34749: :func:`binascii.a2b_base64` is now up to 2 times faster. Patch
by Sergey Fedoseev.

- bpo-34519: Add additional aliases for HP Roman 8. Patch by Michael Osipov.

- bpo-28009: Fix uuid.getnode() on platforms with '.' as MAC Addr delimiter
as well fix for MAC Addr format that omits a leading 0 in MAC Addr values.
Currently, AIX is the only know platform with these settings. Patch by
Michael Felt.

- bpo-30618: Add :meth:`~pathlib.Path.readlink`. Patch by Girts Folkmanis.

- bpo-32498: Made :func:`urllib.parse.unquote()` accept bytes in addition to
strings. Patch by Stein Karlsen.

- bpo-33348: lib2to3 now recognizes expressions after ``*`` and `**` like in
``f(*[] or [])``.

- bpo-32689: Update :func:`shutil.move` function to allow for Path objects
to be used as source argument. Patch by Emily Morehouse and Maxwell
"5.13b" McKinnon.

- bpo-32820: Added __format__ to IPv4 and IPv6 classes. Always outputs a
fully zero- padded string. Supports b/x/n modifiers (bin/hex/native
format). Native format for IPv4 is bin, native format for IPv6 is hex.
Also supports '#' and '_' modifiers.

- bpo-27657: Fix urllib.parse.urlparse() with numeric paths. A string like
"path:80" is no longer parsed as a path but as a scheme ("path") and a
path ("80").

- bpo-4963: Fixed non-deterministic behavior related to mimetypes extension
mapping and module reinitialization.

Documentation
-------------

- bpo-21767: Explicitly mention abc support in functools.singledispatch

- bpo-38816: Provides more details about the interaction between
:c:func:`fork` and CPython's runtime, focusing just on the C-API. This
includes cautions about where :c:func:`fork` should and shouldn't be
called.

- bpo-38351: Modernize :mod:`email` examples from %-formatting to f-strings.

- bpo-38778: Document the fact that :exc:`RuntimeError` is raised if
:meth:`os.fork` is called in a subinterpreter.

- bpo-38592: Add Brazilian Portuguese to the language switcher at Python
Documentation website.

- bpo-38294: Add list of no-longer-escaped chars to re.escape documentation

- bpo-38053: Modernized the plistlib documentation

- bpo-26868: Fix example usage of :c:func:`PyModule_AddObject` to properly
handle errors.

- bpo-36797: Fix a dead link in the distutils API Reference.

- bpo-37977: Warn more strongly and clearly about pickle insecurity

- bpo-37979: Added a link to dateutil.parser.isoparse in the
datetime.fromisoformat documentation. Patch by Paul Ganssle

- bpo-12707: Deprecate info(), geturl(), getcode() methods in favor of the
headers, url, and status properties, respectively, for HTTPResponse and
addinfourl. Also deprecate the code attribute of addinfourl in favor of
the status attribute. Patch by Ashwin Ramaswami

- bpo-37937: Mention ``frame.f_trace`` in :func:`sys.settrace` docs.

- bpo-37878: Make :c:func:`PyThreadState_DeleteCurrent` Internal.

- bpo-37759: Beginning edits to Whatsnew 3.8

- bpo-37726: Stop recommending getopt in the tutorial for command line
argument parsing and promote argparse.

- bpo-32910: Remove implementation-specific behaviour of how venv's
Deactivate works.

- bpo-37256: Fix wording of arguments for :class:`Request` in
:mod:`urllib.request`

- bpo-37284: Add a brief note to indicate that any new
``sys.implementation`` required attributes must go through the PEP
process.

- bpo-30088: Documented that :class:`mailbox.Maildir` constructor doesn't
attempt to verify the maildir folder layout correctness. Patch by
Sviatoslav Sydorenko.

- bpo-37521: Fix `importlib` examples to insert any newly created modules
via importlib.util.module_from_spec() immediately into sys.modules instead
of after calling loader.exec_module().

Thanks to Benjamin Mintz for finding the bug.

- bpo-37456: Slash ('/') is now part of syntax.

- bpo-37487: Fix PyList_GetItem index description to include 0.

- bpo-37149: Replace the dead link to the Tkinter 8.5 reference by John
Shipman, New Mexico Tech, with a link to the archive.org copy.

- bpo-37478: Added possible exceptions to the description of os.chdir().

- bpo-34903: Documented that in :meth:`datetime.datetime.strptime()`, the
leading zero in some two-digit formats is optional. Patch by Mike Gleen.

- bpo-36260: Add decompression pitfalls to zipfile module documentation.

- bpo-37004: In the documentation for difflib, a note was added explicitly
warning that the results of SequenceMatcher's ratio method may depend on
the order of the input strings.

- bpo-36960: Restructured the :mod:`datetime` docs in the interest of making
them more user-friendly and improving readability. Patch by Brad Solomon.

- bpo-36487: Make C-API docs clear about what the "main" interpreter is.

- bpo-23460: The documentation for decimal string formatting using the `:g`
specifier has been updated to reflect the correct exponential notation
cutoff point. Original patch contributed by Tuomas Suutari.

- bpo-35803: Document and test that ``tempfile`` functions may accept a
:term:`path-like object` for the ``dir`` argument. Patch by Anthony
Sottile.

- bpo-33944: Added a note about the intended use of code in .pth files.

- bpo-34293: Fix the Doc/Makefile regarding PAPER environment variable and
PDF builds

- bpo-25237: Add documentation for tkinter modules

Tests
-----

- bpo-38614: Fix test_communicate() of test_asyncio.test_subprocess: use
``support.LONG_TIMEOUT`` (5 minutes), instead of just 1 minute.

- bpo-38614: Add timeout constants to :mod:`test.support`:
:data:`~test.support.LOOPBACK_TIMEOUT`,
:data:`~test.support.INTERNET_TIMEOUT`,
:data:`~test.support.SHORT_TIMEOUT` and
:data:`~test.support.LONG_TIMEOUT`.

- bpo-38502: test.regrtest now uses process groups in the multiprocessing
mode (-jN command line option) if process groups are available: if
:func:`os.setsid` and :func:`os.killpg` functions are available.

- bpo-35998: Fix a race condition in test_asyncio.test_start_tls_server_1().
Previously, there was a race condition between the test main() function
which replaces the protocol and the test ServerProto protocol which sends
ANSWER once it gets HELLO. Now, only the test main() function is
responsible to send data, ServerProto no longer sends data.

- bpo-38470: Fix ``test_compileall.test_compile_dir_maxlevels()`` on Windows
without long path support: only create 3 subdirectories instead of between
20 and 100 subdirectories.

- bpo-37531: On timeout, regrtest no longer attempts to call
``popen.communicate()`` again: it can hang until all child processes using
stdout and stderr pipes completes. Kill the worker process and ignores its
output. Change also the faulthandler timeout of the main process from 1
minute to 5 minutes, for Python slowest buildbots.

- bpo-38239: Fix test_gdb for Link Time Optimization (LTO) builds.

- bpo-38275: test_ssl now handles disabled TLS/SSL versions better.
OpenSSL's crypto policy and run-time settings are recognized and tests for
disabled versions are skipped. Tests also accept more TLS minimum_versions
for platforms that override OpenSSL's default with strict settings.

- bpo-38271: The private keys for test_ssl were encrypted with 3DES in
traditional PKCS#5 format. 3DES and the digest algorithm of PKCS#5 are
blocked by some strict crypto policies. Use PKCS#8 format with AES256
encryption instead.

- bpo-38270: test.support now has a helper function to check for
availability of a hash digest function. Several tests are refactored avoid
MD5 and use SHA256 instead. Other tests are marked to use MD5 and skipped
when MD5 is disabled.

- bpo-37123: Multiprocessing test test_mymanager() now also expects
-SIGTERM, not only exitcode 0. BaseManager._finalize_manager() sends
SIGTERM to the manager process if it takes longer than 1 second to stop,
which happens on slow buildbots.

- bpo-38212: Multiprocessing tests: increase
test_queue_feeder_donot_stop_onexc() timeout from 1 to 60 seconds.

- bpo-38117: Test with OpenSSL 1.1.1d

- bpo-38018: Increase code coverage for multiprocessing.shared_memory.

- bpo-37805: Add tests for json.dump(..., skipkeys=True). Patch by Dong-hee
Na.

- bpo-37531: Enhance regrtest multiprocess timeout: write a message when
killing a worker process, catch popen.kill() and popen.wait() exceptions,
put a timeout on the second call to popen.communicate().

- bpo-37876: Add tests for ROT-13 codec.

- bpo-36833: Added tests for PyDateTime_xxx_GET_xxx() macros of the C API of
the :mod:`datetime` module. Patch by Joannah Nanjekye.

- bpo-37558: Fix test_shared_memory_cleaned_after_process_termination name
handling

- bpo-37526: Add :func:`test.support.catch_threading_exception`: context
manager catching :class:`threading.Thread` exception using
:func:`threading.excepthook`.

- bpo-37421: test_concurrent_futures now explicitly stops the ForkServer
instance if it's running.

- bpo-37421: multiprocessing tests now stop the ForkServer instance if it's
running: close the "alive" file descriptor to ask the server to stop and
then remove its UNIX address.

- bpo-37421: test_distutils.test_build_ext() is now able to remove the
temporary directory on Windows: don't import the newly built C extension
("xx") in the current process, but test it in a separated process.

- bpo-37421: test_concurrent_futures now cleans up multiprocessing to remove
immediately temporary directories created by
multiprocessing.util.get_temp_dir().

- bpo-37421: test_winconsoleio doesn't leak a temporary file anymore: use
tempfile.TemporaryFile() to remove it when the test completes.

- bpo-37421: multiprocessing tests now explicitly call ``_run_finalizers()``
to immediately remove temporary directories created by tests.

- bpo-37421: urllib.request tests now call
:func:`~urllib.request.urlcleanup` to remove temporary files created by
``urlretrieve()`` tests and to clear the ``_opener`` global variable set
by ``urlopen()`` and functions calling indirectly ``urlopen()``.

- bpo-37472: Remove ``Lib/test/outstanding_bugs.py``.

- bpo-37199: Fix test failures when IPv6 is unavailable or disabled.

- bpo-19696: Replace deprecated method "random.choose" with "random.choice"
in "test_pkg_import.py".

- bpo-37335: Remove no longer necessary code from c locale coercion tests

- bpo-37421: Fix test_shutil to no longer leak temporary files.

- bpo-37411: Fix test_wsgiref.testEnviron() to no longer depend on the
environment variables (don't fail if "X" variable is set).

- bpo-37400: Fix test_os.test_chown(): use os.getgroups() rather than
grp.getgrall() to get groups. Rename also the test to test_chown_gid().

- bpo-37359: Add --cleanup option to python3 -m test to remove
``test_python_*`` directories of previous failed jobs. Add "make
cleantest" to run ``python3 -m test --cleanup``.

- bpo-37362: test_gdb no longer fails if it gets an "unexpected" message on
stderr: it now ignores stderr. The purpose of test_gdb is to test that
python-gdb.py commands work as expected, not to test gdb.

- bpo-35998: Avoid TimeoutError in test_asyncio: test_start_tls_server_1()

- bpo-37278: Fix test_asyncio ProactorLoopCtrlC: join the thread to prevent
leaking a running thread and leaking a reference.

- bpo-37261: Fix :func:`test.support.catch_unraisable_exception`: its
__exit__() method now ignores unraisable exception raised when clearing
its ``unraisable`` attribute.

- bpo-37069: regrtest now uses :func:`sys.unraisablehook` to mark a test as
"environment altered" (ENV_CHANGED) if it emits an "unraisable exception".
Moreover, regrtest logs a warning in this case.

Use ``python3 -m test --fail-env-changed`` to catch unraisable exceptions
in tests.

- bpo-37252: Fix assertions in ``test_close`` and
``test_events_mask_overflow`` devpoll tests.

- bpo-37169: Rewrite ``_PyObject_IsFreed()`` unit tests.

- bpo-37153: ``test_venv.test_multiprocessing()`` now explicitly calls
``pool.terminate()`` to wait until the pool completes.

- bpo-34001: Make test_ssl pass with LibreSSL. LibreSSL handles minimum and
maximum TLS version differently than OpenSSL.

- bpo-36919: Make ``test_source_encoding.test_issue2301`` implementation
independent. The test will work now for both CPython and IronPython.

- bpo-30202: Update ``test.test_importlib.test_abc`` to test
``find_spec()``.

- bpo-28009: Modify the test_uuid logic to test when a program is available
AND can be used to obtain a MACADDR as basis for an UUID. Patch by M. Felt

- bpo-34596: Fallback to a default reason when :func:`unittest.skip` is
uncalled. Patch by Naitree Zhu.

Build
-----

- bpo-38809: On Windows, build scripts will now recognize and use python.exe
from an active virtual env.

- bpo-38684: Fix _hashlib build when Blake2 is disabled, but OpenSSL
supports it.

- bpo-38468: Misc/python-config.in now uses `getvar()` for all still
existing `sysconfig.get_config_var()` calls. Patch by Joannah Nanjekye.

- bpo-37415: Fix stdatomic.h header check for ICC compiler: the ICC
implementation lacks atomic_uintptr_t type which is needed by Python.

- bpo-38301: In Solaris family, we must be sure to use ``-D_REENTRANT``.
Patch by Jesús Cea Avión.

- bpo-36002: Locate ``llvm-profdata`` and ``llvm-ar`` binaries using
``AC_PATH_TOOL`` rather than ``AC_PATH_TARGET_TOOL``.

- bpo-37936: The :file:`.gitignore` file systematically keeps "rooted", with
a non-trailing slash, all the rules that are meant to apply to files in a
specific place in the repo. Previously, when the intended file to ignore
happened to be at the root of the repo, we'd most often accidentally also
ignore files and directories with the same name anywhere in the tree.

- bpo-37760: The :file:`Tools/unicode/makeunicodedata.py` script, which is
used for converting information from the Unicode Character Database into
generated code and data used by the methods of :class:`str` and by the
:mod:`unicodedata` module, now handles each character's data as a
``dataclass`` with named attributes, rather than a length-18 list of
different fields.

- bpo-37936: The :file:`.gitignore` file no longer applies to any files that
are in fact tracked in the Git repository. Patch by Greg Price.

- bpo-37725: Change "clean" makefile target to also clean the program guided
optimization (PGO) data. Previously you would have to use "make clean"
and "make profile-removal", or "make clobber".

- bpo-37707: Mark some individual tests to skip when --pgo is used. The
tests marked increase the PGO task time significantly and likely don't
help improve optimization of the final executable.

- bpo-36044: Reduce the number of unit tests run for the PGO generation
task. This speeds up the task by a factor of about 15x. Running the full
unit test suite is slow. This change may result in a slightly less
optimized build since not as many code branches will be executed. If you
are willing to wait for the much slower build, the old behavior can be
restored using './configure [..] PROFILE_TASK="-m test --pgo-extended"'.
We make no guarantees as to which PGO task set produces a faster build.
Users who care should run their own relevant benchmarks as results can
depend on the environment, workload, and compiler tool chain.

- bpo-37468: ``make install`` no longer installs ``wininst-*.exe`` files
used by distutils bdist_wininst: bdist_wininst only works on Windows.

- bpo-37189: Many ``PyRun_XXX()`` functions like :c:func:`PyRun_String` were
no longer exported in ``libpython38.dll`` by mistake. Export them again to
fix the ABI compatibility.

- bpo-25361: Enables use of SSE2 instructions in Windows 32-bit build.

- bpo-36210: Update optional extension module detection for AIX. ossaudiodev
and spwd are not applicable for AIX, and are no longer reported as
missing. 3rd-party packaging of ncurses (with ASIS support) conflicts with
officially supported AIX curses library, so configure AIX to use
libcurses.a. However, skip trying to build _curses_panel.

patch by M Felt

Windows
-------

- bpo-38589: Fixes HTML Help shortcut when Windows is not installed to C
drive

- bpo-38453: Ensure ntpath.realpath() correctly resolves relative paths.

- bpo-38519: Restores the internal C headers that were missing from the
nuget.org and Microsoft Store packages.

- bpo-38492: Remove ``pythonw.exe`` dependency on the Microsoft C++ runtime.

- bpo-38344: Fix error message in activate.bat

- bpo-38359: Ensures ``pyw.exe`` launcher reads correct registry key.

- bpo-38355: Fixes ``ntpath.realpath`` failing on ``sys.executable``.

- bpo-38117: Update bundled OpenSSL to 1.1.1d

- bpo-38092: Reduce overhead when using multiprocessing in a Windows virtual
environment.

- bpo-38133: Allow py.exe launcher to locate installations from the
Microsoft Store and improve display of active virtual environments.

- bpo-38114: The ``pip.ini`` is no longer included in the Nuget package.

- bpo-32592: Set Windows 8 as the minimum required version for API support

- bpo-36634: :func:`os.cpu_count` now returns active processors rather than
maximum processors.

- bpo-36634: venv activate.bat now works when the existing variables contain
double quote characters.

- bpo-38081: Prevent error calling :func:`os.path.realpath` on ``'NUL'``.

- bpo-38087: Fix case sensitivity in test_pathlib and test_ntpath.

- bpo-38088: Fixes distutils not finding vcruntime140.dll with only the v142
toolset installed.

- bpo-37283: Ensure command-line and unattend.xml setting override
previously detected states in Windows installer.

- bpo-38030: Fixes :func:`os.stat` failing for block devices on Windows

- bpo-38020: Fixes potential crash when calling :func:`os.readlink` (or
indirectly through :func:`~os.path.realpath`) on a file that is not a
supported link.

- bpo-37705: Improve the implementation of ``winerror_to_errno()``.

- bpo-37549: :func:`os.dup` no longer fails for standard streams on Windows
7.

- bpo-1311: The ``nul`` file on Windows now returns True from
:func:`~os.path.exists` and a valid result from :func:`os.stat` with
``S_IFCHR`` set.

- bpo-9949: Enable support for following symlinks in :func:`os.realpath`.

- bpo-37834: Treat all name surrogate reparse points on Windows in
:func:`os.lstat` and other reparse points as regular files in
:func:`os.stat`.

- bpo-36266: Add the module name in the formatted error message when DLL
load fail happens during module import in
``_PyImport_FindSharedFuncptrWindows()``. Patch by Srinivas Nyayapati.

- bpo-25172: Trying to import the :mod:`crypt` module on Windows will result
in an :exc:`ImportError` with a message explaining that the module isn't
supported on Windows. On other platforms, if the underlying ``_crypt``
module is not available, the ImportError will include a message explaining
the problem.

- bpo-37778: Fixes the icons used for file associations to the Microsoft
Store package.

- bpo-37734: Fix use of registry values to launch Python from Microsoft
Store app.

- bpo-37702: Fix memory leak on Windows in creating an SSLContext object or
running urllib.request.urlopen('https://...').

- bpo-37672: Switch Windows Store package's pip to use bundled
:file:`pip.ini` instead of :envvar:`PIP_USER` variable.

- bpo-10945: Officially drop support for creating bdist_wininst installers
on non-Windows systems.

- bpo-37445: Include the ``FORMAT_MESSAGE_IGNORE_INSERTS`` flag in
``FormatMessageW()`` calls.

- bpo-37369: Fixes path for :data:`sys.executable` when running from the
Microsoft Store.

- bpo-37380: Don't collect unfinished processes with ``subprocess._active``
on Windows to cleanup later. Patch by Ruslan Kuprieiev.

- bpo-37351: Removes libpython38.a from standard Windows distribution.

- bpo-35360: Update Windows builds to use SQLite 3.28.0.

- bpo-37267: On Windows, :func:`os.dup` no longer creates an inheritable fd
when handling a character file.

- bpo-36779: Ensure ``time.tzname`` is correct on Windows when the active
code page is set to CP_UTF7 or CP_UTF8.

- bpo-32587: Make :data:`winreg.REG_MULTI_SZ` support zero-length strings.

- bpo-28269: Replace use of :c:func:`strcasecmp` for the system function
:c:func:`_stricmp`. Patch by Minmin Gong.

- bpo-36590: Add native Bluetooth RFCOMM support to socket module.

macOS
-----

- bpo-38117: Updated OpenSSL to 1.1.1d in macOS installer.

- bpo-38089: Move Azure Pipelines to latest VM versions and make macOS tests
optional

- bpo-18049: Increase the default stack size of threads from 5MB to 16MB on
macOS, to match the stack size of the main thread. This avoids crashes on
deep recursion in threads.

- bpo-34602: Avoid test suite failures on macOS by no longer calling
resource.setrlimit to increase the process stack size limit at runtime.
The runtime change is no longer needed since the interpreter is being
built with a larger default stack size.

- bpo-35360: Update macOS installer to use SQLite 3.28.0.

- bpo-34631: Updated OpenSSL to 1.1.1c in macOS installer.

IDLE
----

- bpo-26353: Stop adding newline when saving an IDLE shell window.

- bpo-4630: Add an option to toggle IDLE's cursor blink for shell, editor,
and output windows. See Settings, General, Window Preferences, Cursor
Blink. Patch by Zackery Spytz.

- bpo-38598: Do not try to compile IDLE shell or output windows

- bpo-36698: IDLE no longer fails when write non-encodable characters to
stderr. It now escapes them with a backslash, as the regular Python
interpreter. Added the ``errors`` field to the standard streams.

- bpo-35379: When exiting IDLE, catch any AttributeError. One happens when
EditorWindow.close is called twice. Printing a traceback, when IDLE is
run from a terminal, is useless and annoying.

- bpo-38183: To avoid problems, test_idle ignores the user config directory.
It no longer tries to create or access .idlerc or any files within. Users
must run IDLE to discover problems with saving settings.

- bpo-38077: IDLE no longer adds 'argv' to the user namespace when
initializing it. This bug only affected 3.7.4 and 3.8.0b2 to 3.8.0b4.

- bpo-38041: Shell restart lines now fill the window width, always start
with '=', and avoid wrapping unnecessarily. The line will still wrap if
the included file name is long relative to the width.

- bpo-35771: To avoid occasional spurious test_idle failures on slower
machines, increase the ``hover_delay`` in test_tooltip.

- bpo-37824: Properly handle user input warnings in IDLE shell. Cease
turning SyntaxWarnings into SyntaxErrors.

- bpo-37929: IDLE Settings dialog now closes properly when there is no shell
window.

- bpo-37902: Add mousewheel scrolling for IDLE module, path, and stack
browsers. Patch by George Zhang.

- bpo-37849: Fixed completions list appearing too high or low when shown
above the current line.

- bpo-36419: Refactor IDLE autocomplete and improve testing.

- bpo-37748: Reorder the Run menu. Put the most common choice, Run Module,
at the top.

- bpo-37692: Improve highlight config sample with example shell interaction
and better labels for shell elements.

- bpo-37628: Settings dialog no longer expands with font size.

- bpo-37627: Initialize the Customize Run dialog with the command line
arguments most recently entered before. The user can optionally edit
before submitting them.

- bpo-33610: Fix code context not showing the correct context when first
toggled on.

- bpo-37530: Optimize code context to reduce unneeded background activity.
Font and highlight changes now occur along with text changes instead of
after a random delay.

- bpo-27452: Cleanup ``config.py`` by inlining ``RemoveFile`` and
simplifying the handling of ``file`` in ``CreateConfigHandlers``.

- bpo-37325: Fix tab focus traversal order for help source and custom run
dialogs.

- bpo-37321: Both subprocess connection error messages now refer to the
'Startup failure' section of the IDLE doc.

- bpo-17535: Add optional line numbers for IDLE editor windows. Windows
open without line numbers unless set otherwise in the General tab of the
configuration dialog.

- bpo-26806: To compensate for stack frames added by IDLE and avoid possible
problems with low recursion limits, add 30 to limits in the user code
execution process. Subtract 30 when reporting recursion limits to make
this addition mostly transparent.

- bpo-37177: Properly 'attach' search dialogs to their main window so that
they behave like other dialogs and do not get hidden behind their main
window.

- bpo-37039: Adjust "Zoom Height" to individual screens by momentarily
maximizing the window on first use with a particular screen. Changing
screen settings may invalidate the saved height. While a window is
maximized, "Zoom Height" has no effect.

- bpo-35763: Make calltip reminder about '/' meaning positional-only less
obtrusive by only adding it when there is room on the first line.

- bpo-5680: Add 'Run... Customized' to the Run menu to run a module with
customized settings. Any 'command line arguments' entered are added to
sys.argv. One can suppress the normal Shell main module restart.

- bpo-36390: Gather Format menu functions into format.py. Combine
paragraph.py, rstrip.py, and format methods from editor.py.

Tools/Demos
-----------

- bpo-38118: Update Valgrind suppression file to ignore a false alarm in
:c:func:`PyUnicode_Decode` when using GCC builtin strcmp().

- bpo-38347: pathfix.py: Assume all files that end on '.py' are Python
scripts when working recursively.

- bpo-37803: pdb's ``--help`` and ``--version`` long options now work.

- bpo-37942: Improve ArgumentClinic converter for floats.

- bpo-37704: Remove ``Tools/scripts/h2py.py``: use cffi to access a C API in
Python.

- bpo-37675: 2to3 now works when run from a zipped standard library.

- bpo-37034: Argument Clinic now uses the argument name on errors with
keyword-only argument instead of their position. Patch contributed by Rémi
Lapeyre.

- bpo-37064: Add option -k to pathscript.py script: preserve shebang flags.
Add option -a to pathscript.py script: add flags.

C API
-----

- bpo-37633: Re-export some function compatibility wrappers for macros in
``pythonrun.h``.

- bpo-38644: Provide :c:func:`Py_EnterRecursiveCall` and
:c:func:`Py_LeaveRecursiveCall` as regular functions for the limited API.
Previously, there were defined as macros, but these macros didn't work
with the limited API which cannot access ``PyThreadState.recursion_depth``
field. Remove ``_Py_CheckRecursionLimit`` from the stable ABI.

- bpo-38650: The global variable :c:data:`PyStructSequence_UnnamedField` is
now a constant and refers to a constant string.

- bpo-38540: Fixed possible leak in :c:func:`PyArg_Parse` and similar
functions for format units ``"es#"`` and ``"et#"`` when the macro
:c:macro:`PY_SSIZE_T_CLEAN` is not defined.

- bpo-38395: Fix a crash in :class:`weakref.proxy` objects due to incorrect
lifetime management when calling some associated methods that may delete
the last reference to object being referenced by the proxy. Patch by Pablo
Galindo.

- bpo-36389: The ``_PyObject_CheckConsistency()`` function is now also
available in release mode. For example, it can be used to debug a crash in
the ``visit_decref()`` function of the GC.

- bpo-38266: Revert the removal of PyThreadState_DeleteCurrent() with
documentation.

- bpo-38303: Update audioop extension module to use the stable ABI
(PEP-384). Patch by Tyler Kieft.

- bpo-38234: :c:func:`Py_SetPath` now sets :data:`sys.executable` to the
program full path (:c:func:`Py_GetProgramFullPath`) rather than to the
program name (:c:func:`Py_GetProgramName`).

- bpo-38234: Python ignored arguments passed to :c:func:`Py_SetPath`,
:c:func:`Py_SetPythonHome` and :c:func:`Py_SetProgramName`: fix Python
initialization to use specified arguments.

- bpo-38205: The :c:func:`Py_UNREACHABLE` macro now calls
:c:func:`Py_FatalError`.

- bpo-38140: Make dict and weakref offsets opaque for C heap types by
passing the offsets through PyMemberDef

- bpo-15088: The C function ``PyGen_NeedsFinalizing`` has been removed. It
was not documented, tested or used anywhere within CPython after the
implementation of :pep:`442`. Patch by Joannah Nanjekye. (Patch by Joannah
Nanjekye)

- bpo-36763: Options added by ``PySys_AddXOption()`` are now handled the
same way than ``PyConfig.xoptions`` and command line ``-X`` options.

- bpo-37926: Fix a crash in ``PySys_SetArgvEx(0, NULL, 0)``.

- bpo-37879: Fix subtype_dealloc to suppress the type decref when the base
type is a C heap type

- bpo-37645: Add :c:func:`_PyObject_FunctionStr` to get a user-friendly
string representation of a function-like object. Patch by Jeroen Demeyer.

- bpo-29548: The functions ``PyEval_CallObject``, ``PyEval_CallFunction``,
``PyEval_CallMethod`` and ``PyEval_CallObjectWithKeywords`` are
deprecated. Use :c:func:`PyObject_Call` and its variants instead.

- bpo-37151: ``PyCFunction_Call`` is now a deprecated alias of
:c:func:`PyObject_Call`.

- bpo-37540: The vectorcall protocol now requires that the caller passes
only strings as keyword names.

- bpo-37207: The vectorcall protocol is now enabled for ``type`` objects:
set ``tp_vectorcall`` to a vectorcall function to be used instead of
``tp_new`` and ``tp_init`` when calling the class itself.

- bpo-21120: Exclude Python-ast.h, ast.h and asdl.h from the limited API.

- bpo-37483: Add new function ``_PyObject_CallOneArg`` for calling an object
with one positional argument.

- bpo-36763: Add :func:`PyConfig_SetWideStringList` function.

- bpo-37337: Add fast functions for calling methods:
:c:func:`_PyObject_VectorcallMethod`, :c:func:`_PyObject_CallMethodNoArgs`
and :c:func:`_PyObject_CallMethodOneArg`.

- bpo-28805: The :const:`METH_FASTCALL` calling convention has been
documented.

- bpo-37221: The new function :c:func:`PyCode_NewWithPosOnlyArgs` allows to
create code objects like :c:func:`PyCode_New`, but with an extra
*posonlyargcount* parameter for indicating the number of positonal-only
arguments.

- bpo-37215: Fix dtrace issue introduce by bpo-36842

- bpo-37194: Add a new public :c:func:`PyObject_CallNoArgs` function to the
C API: call a callable Python object without any arguments. It is the most
efficient way to call a callback without any argument. On x86-64, for
example, ``PyObject_CallFunctionObjArgs(func, NULL)`` allocates 960 bytes
on the stack per call, whereas ``PyObject_CallNoArgs(func)`` only
allocates 624 bytes per call.

- bpo-37170: Fix the cast on error in
:c:func:`PyLong_AsUnsignedLongLongMask()`.

- bpo-35381: Convert posixmodule.c statically allocated types
``DirEntryType`` and ``ScandirIteratorType`` to heap-allocated types.

- bpo-34331: Use singular/plural noun in error message when instantiating an
abstract class with non-overriden abstract method(s).

What's New in Python 3.8.0 beta 1?
==================================

*Release date: 2019-06-04*

Security
--------

- bpo-35907: CVE-2019-9948: Avoid file reading by disallowing
``local-file://`` and ``local_file://`` URL schemes in
``URLopener().open()`` and ``URLopener().retrieve()`` of
:mod:`urllib.request`.

- bpo-33529: Prevent fold function used in email header encoding from
entering infinite loop when there are too many non-ASCII characters in a
header.

- bpo-33164: Updated blake2 implementation which uses secure memset
implementation provided by platform.

Core and Builtins
-----------------

- bpo-35814: Allow unpacking in the right hand side of annotated
assignments. In particular, ``t: Tuple[int, ...] = x, y, *z`` is now
allowed.

- bpo-37126: All structseq objects are now tracked by the garbage collector.
Patch by Pablo Galindo.

- bpo-37122: Make the *co_argcount* attribute of code objects represent the
total number of positional arguments (including positional-only
arguments). The value of *co_posonlyargcount* can be used to distinguish
which arguments are positional only, and the difference (*co_argcount* -
*co_posonlyargcount*) is the number of positional-or-keyword arguments.
Patch by Pablo Galindo.

- bpo-20092: Constructors of :class:`int`, :class:`float` and
:class:`complex` will now use the :meth:`~object.__index__` special
method, if available and the corresponding method :meth:`~object.__int__`,
:meth:`~object.__float__` or :meth:`~object.__complex__` is not available.

- bpo-37087: Add native thread ID (TID) support to OpenBSD.

- bpo-26219: Implemented per opcode cache mechanism and ``LOAD_GLOBAL``
instruction use it. ``LOAD_GLOBAL`` is now about 40% faster. Contributed
by Yury Selivanov, and Inada Naoki.

- bpo-37072: Fix crash in PyAST_FromNodeObject() when flags is NULL.

- bpo-37029: Freeing a great many small objects could take time quadratic in
the number of arenas, due to using linear search to keep ``obmalloc.c``'s
list of usable arenas sorted by order of number of free memory pools.
This is accomplished without search now, leaving the worst-case time
linear in the number of arenas. For programs where this quite visibly
matters (typically with more than 100 thousand small objects alive
simultaneously), this can greatly reduce the time needed to release their
memory.

- bpo-26423: Fix possible overflow in ``wrap_lenfunc()`` when ``sizeof(long)
< sizeof(Py_ssize_t)`` (e.g., 64-bit Windows).

- bpo-37050: Improve the AST for "debug" f-strings, which use '=' to print
out the source of the expression being evaluated. Delete expr_text from
the FormattedValue node, and instead use a Constant string node (possibly
merged with adjacent constant expressions inside the f-string).

- bpo-22385: The `bytes.hex`, `bytearray.hex`, and `memoryview.hex` methods
as well as the `binascii.hexlify` and `b2a_hex` functions now have the
ability to include an optional separator between hex bytes. This
functionality was inspired by MicroPython's hexlify implementation.

- bpo-26836: Add :func:`os.memfd_create`.

- bpo-37032: Added new ``replace()`` method to the code type
(:class:`types.CodeType`).

- bpo-37007: Implement :func:`socket.if_nameindex()`,
:func:`socket.if_nametoindex()`, and :func:`socket.if_indextoname()` on
Windows.

- bpo-36829: :c:func:`PyErr_WriteUnraisable` now creates a traceback object
if there is no current traceback. Moreover, call
:c:func:`PyErr_NormalizeException` and :c:func:`PyException_SetTraceback`
to normalize the exception value. Ignore any error.

- bpo-36878: Only accept text after `# type: ignore` if the first character
is ASCII. This is to disallow things like `# type: ignoreé`.

- bpo-36878: Store text appearing after a `# type: ignore` comment in the
AST. For example a type ignore like `# type: ignore[E1000]` will have the
string `"[E1000]"` stored in its AST node.

- bpo-2180: Treat line continuation at EOF as a ``SyntaxError`` by Anthony
Sottile.

- bpo-36907: Fix a crash when calling a C function with a keyword dict
(``f(**kwargs)``) and changing the dict ``kwargs`` while that function is
running.

- bpo-36946: Fix possible signed integer overflow when handling slices.

- bpo-36826: Add NamedExpression kind support to ast_unparse.c

- bpo-1875: A :exc:`SyntaxError` is now raised if a code blocks that will be
optimized away (e.g. if conditions that are always false) contains syntax
errors. Patch by Pablo Galindo.

- bpo-36027: Allow computation of modular inverses via three-argument
``pow``: the second argument is now permitted to be negative in the case
where the first and third arguments are relatively prime.

- bpo-36861: Update the Unicode database to version 12.1.0.

- bpo-28866: Avoid caching attributes of classes which type defines mro() to
avoid a hard cache invalidation problem.

- bpo-36851: The ``FrameType`` stack is now correctly cleaned up if the
execution ends with a return and the stack is not empty.

- bpo-34616: The ``compile()`` builtin functions now support the
``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` flag, which allow to compile sources
that contains top-level ``await``, ``async with`` or ``async for``. This
is useful to evaluate async-code from with an already async functions; for
example in a custom REPL.

- bpo-36842: Implement PEP 578, adding sys.audit, io.open_code and related
APIs.

- bpo-27639: Correct return type for UserList slicing operations. Patch by
Michael Blahay, Erick Cervantes, and vaultah

- bpo-36737: Move PyRuntimeState.warnings into per-interpreter state (via
"module state").

- bpo-36793: Removed ``__str__`` implementations from builtin types
:class:`bool`, :class:`int`, :class:`float`, :class:`complex` and few
classes from the standard library. They now inherit ``__str__()`` from
:class:`object`.

- bpo-36817: Add a ``=`` feature f-strings for debugging. This can precede
``!s``, ``!r``, or ``!a``. It produces the text of the expression,
followed by an equal sign, followed by the repr of the value of the
expression. So ``f'{3*9+15=}'`` would be equal to the string
``'3*9+15=42'``. If ``=`` is specified, the default conversion is set to
``!r``, unless a format spec is given, in which case the formatting
behavior is unchanged, and __format__ will be used.

- bpo-24048: Save the live exception during import.c's ``remove_module()``.

- bpo-27987: pymalloc returns memory blocks aligned by 16 bytes, instead of
8 bytes, on 64-bit platforms to conform x86-64 ABI. Recent compilers
assume this alignment more often. Patch by Inada Naoki.

- bpo-36601: A long-since-meaningless check for ``getpid() == main_pid`` was
removed from Python's internal C signal handler.

- bpo-36594: Fix incorrect use of ``%p`` in format strings. Patch by Zackery
Spytz.

- bpo-36045: builtins.help() now prefixes `async` for async functions

- bpo-36084: Add native thread ID (TID) to threading.Thread objects
(supported platforms: Windows, FreeBSD, Linux, macOS)

- bpo-36035: Added fix for broken symlinks in combination with pathlib

- bpo-35983: Added new trashcan macros to deal with a double deallocation
that could occur when the `tp_dealloc` of a subclass calls the
`tp_dealloc` of a base class and that base class uses the trashcan
mechanism. Patch by Jeroen Demeyer.

- bpo-20602: Do not clear :data:`sys.flags` and :data:`sys.float_info`
during shutdown. Patch by Zackery Spytz.

- bpo-26826: Expose :func:`copy_file_range` as a low level API in the
:mod:`os` module.

- bpo-32388: Remove cross-version binary compatibility requirement in
tp_flags.

- bpo-31862: Port binascii to PEP 489 multiphase initialization. Patch by
Marcel Plch.

Library
-------

- bpo-37128: Added :func:`math.perm`.

- bpo-37120: Add SSLContext.num_tickets to control the number of TLSv1.3
session tickets.

- bpo-12202: Fix the error handling in
:meth:`msilib.SummaryInformation.GetProperty`. Patch by Zackery Spytz.

- bpo-26835: The fcntl module now contains file sealing constants for
sealing of memfds.

- bpo-29262: Add ``get_origin()`` and ``get_args()`` introspection helpers
to ``typing`` module.

- bpo-12639: :meth:`msilib.Directory.start_component()` no longer fails if
*keyfile* is not ``None``.

- bpo-36999: Add the ``asyncio.Task.get_coro()`` method to publicly expose
the tasks's coroutine object.

- bpo-35246: Make :func:`asyncio.create_subprocess_exec` accept path-like
arguments.

- bpo-35279: Change default *max_workers* of ``ThreadPoolExecutor`` from
``cpu_count() * 5`` to ``min(32, cpu_count() + 4)``. Previous value was
unreasonably large on many cores machines.

- bpo-37076: :func:`_thread.start_new_thread` now logs uncaught exception
raised by the function using :func:`sys.unraisablehook`, rather than
:func:`sys.excepthook`, so the hook gets access to the function which
raised the exception.

- bpo-33725: On macOS, the :mod:`multiprocessing` module now uses *spawn*
start method by default.

- bpo-37054: Fix destructor :class:`_pyio.BytesIO` and
:class:`_pyio.TextIOWrapper`: initialize their ``_buffer`` attribute as
soon as possible (in the class body), because it's used by ``__del__()``
which calls ``close()``.

- bpo-37058: PEP 544: Add ``Protocol`` and ``@runtime_checkable`` to the
``typing`` module.

- bpo-36933: The functions ``sys.set_coroutine_wrapper`` and
``sys.get_coroutine_wrapper`` that were deprecated and marked for removal
in 3.8 have been removed.

- bpo-37047: Handle late binding and attribute access in
:class:`unittest.mock.AsyncMock` setup for autospeccing. Document newly
implemented async methods in :class:`unittest.mock.MagicMock`.

- bpo-37049: PEP 589: Add ``TypedDict`` to the ``typing`` module.

- bpo-37046: PEP 586: Add ``Literal`` to the ``typing`` module.

- bpo-37045: PEP 591: Add ``Final`` qualifier and ``@final`` decorator to
the ``typing`` module.

- bpo-37035: Don't log OSError based exceptions if a fatal error has
occurred in asyncio transport. Peer can generate almost any OSError, user
cannot avoid these exceptions by fixing own code. Errors are still
propagated to user code, it's just logging them is pointless and pollute
asyncio logs.

- bpo-37001: :func:`symtable.symtable` now accepts the same input types for
source code as the built-in :func:`compile` function. Patch by Dino
Viehland.

- bpo-37028: Implement asyncio REPL

- bpo-37027: Return safe to use proxy socket object from
transport.get_extra_info('socket')

- bpo-32528: Make asyncio.CancelledError a BaseException.

This will address the common mistake many asyncio users make: an "except
Exception" clause breaking Tasks cancellation.

In addition to this change, we stop inheriting asyncio.TimeoutError and
asyncio.InvalidStateError from their concurrent.futures.* counterparts.
There's no point for these exceptions to share the inheritance chain.

- bpo-1230540: Add a new :func:`threading.excepthook` function which handles
uncaught :meth:`threading.Thread.run` exception. It can be overridden to
control how uncaught :meth:`threading.Thread.run` exceptions are handled.

- bpo-36996: Handle :func:`unittest.mock.patch` used as a decorator on async
functions.

- bpo-37008: Add support for calling :func:`next` with the mock resulting
from :func:`unittest.mock.mock_open`

- bpo-27737: Allow whitespace only header encoding in ``email.header`` - by
Batuhan Taskaya

- bpo-36969: PDB command `args` now display positional only arguments.
Patch contributed by Rémi Lapeyre.

- bpo-36969: PDB command `args` now display keyword only arguments. Patch
contributed by Rémi Lapeyre.

- bpo-36983: Add missing names to ``typing.__all__``: ``ChainMap``,
``ForwardRef``, ``OrderedDict`` - by Anthony Sottile.

- bpo-36972: Add SupportsIndex protocol to the typing module to allow type
checking to detect classes that can be passed to `hex()`, `oct()` and
`bin()`.

- bpo-32972: Implement ``unittest.IsolatedAsyncioTestCase`` to help testing
asyncio-based code.

- bpo-36952: :func:`fileinput.input` and :class:`fileinput.FileInput`
**bufsize** argument has been removed (was deprecated and ignored since
Python 3.6), and as a result the **mode** and **openhook** arguments have
been made keyword-only.

- bpo-36952: Starting with Python 3.3, importing ABCs from
:mod:`collections` is deprecated, and import should be done from
:mod:`collections.abc`. Still being able to import from :mod:`collections`
was marked for removal in 3.8, but has been delayed to 3.9; documentation
and ``DeprecationWarning`` clarified.

- bpo-36949: Implement __repr__ for WeakSet objects.

- bpo-36948: Fix :exc:`NameError` in
:meth:`urllib.request.URLopener.retrieve`. Patch by Karthikeyan
Singaravelan.

- bpo-33524: Fix the folding of email header when the max_line_length is 0
or None and the header contains non-ascii characters. Contributed by
Licht Takeuchi (@Licht-T).

- bpo-24564: :func:`shutil.copystat` now ignores :const:`errno.EINVAL` on
:func:`os.setxattr` which may occur when copying files on filesystems
without extended attributes support.

Original patch by Giampaolo Rodola, updated by Ying Wang.

- bpo-36888: Python child processes can now access the status of their
parent process using multiprocessing.process.parent_process

- bpo-36921: Deprecate ``@coroutine`` for sake of ``async def``.

- bpo-25652: Fix bug in ``__rmod__`` of ``UserString`` - by Batuhan Taskaya.

- bpo-36916: Remove a message about an unhandled exception in a task when
writer.write() is used without await and writer.drain() fails with an
exception.

- bpo-36889: Introduce :class:`asyncio.Stream` class that merges
:class:`asyncio.StreamReader` and :class:`asyncio.StreamWriter`
functionality. :class:`asyncio.Stream` can work in readonly, writeonly and
readwrite modes. Provide :func:`asyncio.connect`,
:func:`asyncio.connect_unix`, :func:`asyncio.connect_read_pipe` and
:func:`asyncio.connect_write_pipe` factories to open
:class:`asyncio.Stream` connections. Provide :class:`asyncio.StreamServer`
and :class:`UnixStreamServer` to serve servers with asyncio.Stream API.
Modify :func:`asyncio.create_subprocess_shell` and
:func:`asyncio.create_subprocess_exec` to use :class:`asyncio.Stream`
instead of deprecated :class:`StreamReader` and :class:`StreamWriter`.
Deprecate :class:`asyncio.StreamReader` and :class:`asyncio.StreamWriter`.
Deprecate usage of private classes, e.g.
:class:`asyncio.FlowControlMixing` and
:class:`asyncio.StreamReaderProtocol` outside of asyncio package.

- bpo-36845: Added validation of integer prefixes to the construction of IP
networks and interfaces in the ipaddress module.

- bpo-23378: Add an extend action to argparser.

- bpo-36867: Fix a bug making a SharedMemoryManager instance and its parent
process use two separate resource_tracker processes.

- bpo-23896: Adds a grammar to lib2to3.pygram that contains exec as a
function not as statement.

- bpo-36895: The function ``time.clock()`` was deprecated in 3.3 in favor of
``time.perf_counter()`` and marked for removal in 3.8, it has removed.

- bpo-35545: Fix asyncio discarding IPv6 scopes when ensuring hostname
resolutions internally

- bpo-36887: Add new function :func:`math.isqrt` to compute integer square
roots.

- bpo-34632: Introduce the ``importlib.metadata`` module with (provisional)
support for reading metadata from third-party packages.

- bpo-36878: When using `type_comments=True` in `ast.parse`, treat `# type:
ignore` followed by a non-alphanumeric character and then arbitrary text
as a type ignore, instead of requiring nothing but whitespace or another
comment. This is to permit formations such as `# type: ignore[E1000]`.

- bpo-36778: ``cp65001`` encoding (Windows code page 65001) becomes an alias
to ``utf_8`` encoding.

- bpo-36867: The multiprocessing.resource_tracker replaces the
multiprocessing.semaphore_tracker module. Other than semaphores,
resource_tracker also tracks shared_memory segments.

- bpo-30262: The ``Cache`` and ``Statement`` objects of the :mod:`sqlite3`
module are not exposed to the user. Patch by Aviv Palivoda.

- bpo-24538: In `shutil.copystat()`, first copy extended file attributes and
then file permissions, since extended attributes can only be set on the
destination while it is still writeable.

- bpo-36829: Add new :func:`sys.unraisablehook` function which can be
overridden to control how "unraisable exceptions" are handled. It is
called when an exception has occurred but there is no way for Python to
handle it. For example, when a destructor raises an exception or during
garbage collection (:func:`gc.collect`).

- bpo-36832: Introducing ``zipfile.Path``, a pathlib-compatible wrapper for
traversing zip files.

- bpo-36814: Fix an issue where os.posix_spawnp() would incorrectly raise a
TypeError when file_actions is None.

- bpo-33110: Handle exceptions raised by functions added by
concurrent.futures add_done_callback correctly when the Future has already
completed.

- bpo-26903: Limit `max_workers` in `ProcessPoolExecutor` to 61 to work
around a WaitForMultipleObjects limitation.

- bpo-36813: Fix :class:`~logging.handlers.QueueListener` to call
``queue.task_done()`` upon stopping. Patch by Bar Harel.

- bpo-36806: Forbid creation of asyncio stream objects like StreamReader,
StreamWriter, Process, and their protocols outside of asyncio package.

- bpo-36802: Provide both sync and async calls for StreamWriter.write() and
StreamWriter.close()

- bpo-36801: Properly handle SSL connection closing in asyncio
StreamWriter.drain() call.

- bpo-36785: Implement PEP 574 (pickle protocol 5 with out-of-band buffers).

- bpo-36772: functools.lru_cache() can now be used as a straight decorator
in addition to its existing usage as a function that returns a decorator.

- bpo-6584: Add a :exc:`~gzip.BadGzipFile` exception to the :mod:`gzip`
module.

- bpo-36748: Optimized write buffering in C implementation of
``TextIOWrapper``. Writing ASCII string to ``TextIOWrapper`` with ascii,
latin1, or utf-8 encoding is about 20% faster. Patch by Inada Naoki.

- bpo-8138: Don't mark ``wsgiref.simple_server.SimpleServer`` as
multi-threaded since ``wsgiref.simple_server.WSGIServer`` is
single-threaded.

- bpo-22640: :func:`py_compile.compile` now supports silent mode. Patch by
Joannah Nanjekye

- bpo-29183: Fix double exceptions in :class:`wsgiref.handlers.BaseHandler`
by calling its :meth:`~wsgiref.handlers.BaseHandler.close` method only
when no exception is raised.

- bpo-36548: Improved the repr of regular expression flags.

- bpo-36542: The signature of Python functions can now be overridden by
specifying the ``__text_signature__`` attribute.

- bpo-36533: Reinitialize logging.Handler locks in forked child processes
instead of attempting to acquire them all in the parent before forking
only to be released in the child process. The acquire/release pattern was
leading to deadlocks in code that has implemented any form of chained
logging handlers that depend upon one another as the lock acquisition
order cannot be guaranteed.

- bpo-35252: Throw a TypeError instead of an AssertionError when using an
invalid type annotation with singledispatch.

- bpo-35900: Allow reduction methods to return a 6-item tuple where the 6th
item specifies a custom state-setting method that's called instead of the
regular ``__setstate__`` method.

- bpo-35900: enable custom reduction callback registration for functions and
classes in _pickle.c, using the new Pickler's attribute
``reducer_override``

- bpo-36368: Fix a bug crashing SharedMemoryManager instances in interactive
sessions after a ctrl-c (KeyboardInterrupt) was sent

- bpo-31904: Fix mmap fail for VxWorks

- bpo-27497: :meth:`csv.DictWriter.writeheader` now returns the return value
of the underlying :meth:`csv.Writer.writerow` method. Patch contributed by
Ashish Nitin Patil.

- bpo-36239: Parsing .mo files now ignores comments starting and ending with
#-#-#-#-#.

- bpo-26707: Enable plistlib to read and write binary plist files that were
created as a KeyedArchive file. Specifically, this allows the plistlib to
process 0x80 tokens as UID objects.

- bpo-31904: Add posix module support for VxWorks.

- bpo-35125: Asyncio: Remove inner callback on outer cancellation in shield

- bpo-35721: Fix :meth:`asyncio.SelectorEventLoop.subprocess_exec()` leaks
file descriptors if ``Popen`` fails and called with
``stdin=subprocess.PIPE``. Patch by Niklas Fiekas.

- bpo-31855: :func:`unittest.mock.mock_open` results now respects the
argument of read([size]). Patch contributed by Rémi Lapeyre.

- bpo-35431: Implement :func:`math.comb` that returns binomial coefficient,
that computes the number of ways to choose k items from n items without
repetition and without order. Patch by Yash Aggarwal and Keller Fuchs.

- bpo-26660: Fixed permission errors in
:class:`~tempfile.TemporaryDirectory` clean up. Previously
``TemporaryDirectory.cleanup()`` failed when non-writeable or
non-searchable files or directories were created inside a temporary
directory.

- bpo-34271: Add debugging helpers to ssl module. It's now possible to dump
key material and to trace TLS protocol. The default and stdlib contexts
also support SSLKEYLOGFILE env var.

- bpo-26467: Added AsyncMock to support using unittest to mock asyncio
coroutines. Patch by Lisa Roach.

- bpo-33569: dataclasses.InitVar: Exposes the type used to create the init
var.

- bpo-34424: Fix serialization of messages containing encoded strings when
the policy.linesep is set to a multi-character string. Patch by Jens
Troeger.

- bpo-34303: Performance of :func:`functools.reduce` is slightly improved.
Patch by Sergey Fedoseev.

- bpo-33361: Fix a bug in :class:`codecs.StreamRecoder` where seeking might
leave old data in a buffer and break subsequent read calls. Patch by Ammar
Askar.

- bpo-22454: The :mod:`shlex` module now exposes :func:`shlex.join`, the
inverse of :func:`shlex.split`. Patch by Bo Bayles.

- bpo-31922: :meth:`asyncio.AbstractEventLoop.create_datagram_endpoint`: Do
not connect UDP socket when broadcast is allowed. This allows to receive
replies after a UDP broadcast.

- bpo-24882: Change ThreadPoolExecutor to use existing idle threads before
spinning up new ones.

- bpo-31961: Added support for bytes and path-like objects in
:func:`subprocess.Popen` on Windows. The *args* parameter now accepts a
:term:`path-like object` if *shell* is ``False`` and a sequence containing
bytes and path-like objects. The *executable* parameter now accepts a
bytes and :term:`path-like object`. The *cwd* parameter now accepts a
bytes object. Based on patch by Anders Lorentsen.

- bpo-33123: :class:`pathlib.Path.unlink` now accepts a *missing_ok*
parameter to avoid a :exc:`FileNotFoundError` from being raised. Patch by
Robert Buchholz.

- bpo-32941: Allow :class:`mmap.mmap` objects to access the madvise() system
call (through :meth:`mmap.mmap.madvise`).

- bpo-22102: Added support for ZIP files with disks set to 0. Such files are
commonly created by builtin tools on Windows when use ZIP64 extension.
Patch by Francisco Facioni.

- bpo-32515: trace.py can now run modules via python3 -m trace -t --module
module_name

- bpo-32299: Changed :func:`unittest.mock.patch.dict` to return the patched
dictionary when used as context manager. Patch by Vadim Tsander.

- bpo-27141: Added a ``__copy__()`` to ``collections.UserList`` and
``collections.UserDict`` in order to correctly implement shallow copying
of the objects. Patch by Bar Harel.

- bpo-31829: ``\r``, ``\0`` and ``\x1a`` (end-of-file on Windows) are now
escaped in protocol 0 pickles of Unicode strings. This allows to load them
without loss from files open in text mode in Python 2.

- bpo-23395: ``_thread.interrupt_main()`` now avoids setting the Python
error status if the ``SIGINT`` signal is ignored or not handled by Python.

Documentation
-------------

- bpo-36896: Clarify that some types have unstable constructor signature
between Python versions.

- bpo-36686: Improve documentation of the stdin, stdout, and stderr
arguments of the ``asyncio.subprocess_exec`` function to specify which
values are supported. Also mention that decoding as text is not supported.

Add a few tests to verify that the various values passed to the std*
arguments actually work.

- bpo-36984: Improve version added references in ``typing`` module - by
Anthony Sottile.

- bpo-36868: What's new now mentions SSLContext.hostname_checks_common_name
instead of SSLContext.host_flags.

- bpo-35924: Add a note to the ``curses.addstr()`` documentation to warn
that multiline strings can cause segfaults because of an ncurses bug.

- bpo-36783: Added C API Documentation for Time_FromTimeAndFold and
PyDateTime_FromDateAndTimeAndFold as per PEP 495. Patch by Edison
Abahurire.

- bpo-36797: More of the legacy distutils documentation has been either
pruned, or else more clearly marked as being retained solely until the
setuptools documentation covers it independently.

- bpo-22865: Add detail to the documentation on the `pty.spawn` function.

- bpo-35397: Remove deprecation and document urllib.parse.unwrap(). Patch
contributed by Rémi Lapeyre.

- bpo-32995: Added the context variable in glossary.

- bpo-33519: Clarify that `copy()` is not part of the `MutableSequence` ABC.

- bpo-33482: Make `codecs.StreamRecoder.writelines` take a list of bytes.

- bpo-25735: Added documentation for func factorial to indicate that returns
integer values

- bpo-20285: Expand object.__doc__ (docstring) to make it clearer. Modify
pydoc.py so that help(object) lists object methods (for other classes,
help omits methods of the object base class.)

Tests
-----

- bpo-37069: Modify test_coroutines, test_cprofile, test_generators,
test_raise, test_ssl and test_yield_from to use
:func:`test.support.catch_unraisable_exception` rather than
:func:`test.support.captured_stderr`.

- bpo-37098: Fix test_memfd_create on older Linux Kernels.

- bpo-37081: Test with OpenSSL 1.1.1c

- bpo-36829: Add :func:`test.support.catch_unraisable_exception`: context
manager catching unraisable exception using :func:`sys.unraisablehook`.

- bpo-36915: The main regrtest process now always removes all temporary
directories of worker processes even if they crash or if they are killed
on KeyboardInterrupt (CTRL+c).

- bpo-36719: "python3 -m test -jN ..." now continues the execution of next
tests when a worker process crash (CHILD_ERROR state). Previously, the
test suite stopped immediately. Use --failfast to stop at the first error.

- bpo-36816: Update Lib/test/selfsigned_pythontestdotnet.pem to match
self-signed.pythontest.net's new TLS certificate.

- bpo-35925: Skip httplib and nntplib networking tests when they would
otherwise fail due to a modern OS or distro with a default OpenSSL policy
of rejecting connections to servers with weak certificates.

- bpo-36782: Add tests for several C API functions in the :mod:`datetime`
module. Patch by Edison Abahurire.

- bpo-36342: Fix test_multiprocessing in test_venv if platform lacks
functioning sem_open.

Build
-----

- bpo-36721: To embed Python into an application, a new ``--embed`` option
must be passed to ``python3-config --libs --embed`` to get ``-lpython3.8``
(link the application to libpython). To support both 3.8 and older, try
``python3-config --libs --embed`` first and fallback to ``python3-config
--libs`` (without ``--embed``) if the previous command fails.

Add a pkg-config ``python-3.8-embed`` module to embed Python into an
application: ``pkg-config python-3.8-embed --libs`` includes
``-lpython3.8``. To support both 3.8 and older, try ``pkg-config
python-X.Y-embed --libs`` first and fallback to ``pkg-config python-X.Y
--libs`` (without ``--embed``) if the previous command fails (replace
``X.Y`` with the Python version).

On the other hand, ``pkg-config python3.8 --libs`` no longer contains
``-lpython3.8``. C extensions must not be linked to libpython (except on
Android, case handled by the script); this change is backward incompatible
on purpose.

- bpo-36786: "make install" now runs compileall in parallel.

Windows
-------

- bpo-36965: include of STATUS_CONTROL_C_EXIT without depending on MSC
compiler

- bpo-35926: Update to OpenSSL 1.1.1b for Windows.

- bpo-29883: Add Windows support for UDP transports for the Proactor Event
Loop. Patch by Adam Meily.

- bpo-33407: The :c:macro:`Py_DEPRECATED()` macro has been implemented for
MSVC.

macOS
-----

- bpo-36231: Support building Python on macOS without /usr/include
installed. As of macOS 10.14, system header files are only available
within an SDK provided by either the Command Line Tools or the Xcode app.

IDLE
----

- bpo-35610: Replace now redundant .context_use_ps1 with .prompt_last_line.
This finishes change started in bpo-31858.

- bpo-37038: Make idlelib.run runnable; add test clause.

- bpo-36958: Print any argument other than None or int passed to SystemExit
or sys.exit().

- bpo-36807: When saving a file, call os.fsync() so bits are flushed to e.g.
USB drive.

- bpo-32411: In browser.py, remove extraneous sorting by line number since
dictionary was created in line number order.

Tools/Demos
-----------

- bpo-37053: Handle strings like u"bar" correctly in
Tools/parser/unparse.py. Patch by Chih-Hsuan Yen.

C API
-----

- bpo-36763: Implement the :pep:`587` "Python Initialization Configuration".

- bpo-36379: Fix crashes when attempting to use the *modulo* parameter when
``__ipow__`` is implemented in C.

- bpo-37107: Update :c:func:`PyObject_CallMethodObjArgs` and
``_PyObject_CallMethodIdObjArgs`` to use ``_PyObject_GetMethod`` to avoid
creating a bound method object in many cases. Patch by Michael J.
Sullivan.

- bpo-36974: Implement :pep:`590`: Vectorcall: a fast calling protocol for
CPython. This is a new protocol to optimize calls of custom callable
objects.

- bpo-36763: ``Py_Main()`` now returns the exitcode rather than calling
``Py_Exit(exitcode)`` when calling ``PyErr_Print()`` if the current
exception type is ``SystemExit``.

- bpo-36922: Add new type flag ``Py_TPFLAGS_METHOD_DESCRIPTOR`` for objects
behaving like unbound methods. These are objects supporting the
optimization given by the ``LOAD_METHOD``/``CALL_METHOD`` opcodes. See PEP
590.

- bpo-36728: The :c:func:`PyEval_ReInitThreads` function has been removed
from the C API. It should not be called explicitly: use
:c:func:`PyOS_AfterFork_Child` instead.

What's New in Python 3.8.0 alpha 4?
===================================

*Release date: 2019-05-06*

Security
--------

- bpo-36742: Fixes mishandling of pre-normalization characters in
urlsplit().

- bpo-30458: Address CVE-2019-9740 by disallowing URL paths with embedded
whitespace or control characters through into the underlying http client
request. Such potentially malicious header injection URLs now cause an
http.client.InvalidURL exception to be raised.

- bpo-35755: :func:`shutil.which` now uses ``os.confstr("CS_PATH")`` if
available and if the :envvar:`PATH` environment variable is not set.
Remove also the current directory from :data:`posixpath.defpath`. On Unix,
:func:`shutil.which` and the :mod:`subprocess` module no longer search the
executable in the current directory if the :envvar:`PATH` environment
variable is not set.

Core and Builtins
-----------------

- bpo-36722: In debug build, import now also looks for C extensions compiled
in release mode and for C extensions compiled in the stable ABI.

- bpo-32849: Fix Python Initialization code on FreeBSD to detect properly
when stdin file descriptor (fd 0) is invalid.

- bpo-36623: Remove parser headers and related function declarations that
lack implementations after the removal of pgen.

- bpo-20180: ``dict.pop()`` is now up to 33% faster thanks to Argument
Clinic. Patch by Inada Naoki.

- bpo-36611: Debug memory allocators: disable serialno field by default from
debug hooks on Python memory allocators to reduce the memory footprint by
5%. Enable :mod:`tracemalloc` to get the traceback where a memory block
has been allocated when a fatal memory error is logged to decide where to
put a breakpoint. Compile Python with ``PYMEM_DEBUG_SERIALNO`` defined to
get back the field.

- bpo-36588: On AIX, :attr:`sys.platform` doesn't contain the major version
anymore. Always return ``'aix'``, instead of ``'aix3'`` .. ``'aix7'``.
Since older Python versions include the version number, it is recommended
to always use ``sys.platform.startswith('aix')``. Contributed by M. Felt.

- bpo-36549: Change str.capitalize to use titlecase for the first character
instead of uppercase.

- bpo-36540: Implement :pep:`570` (Python positional-only parameters). Patch
by Pablo Galindo.

- bpo-36475: :c:func:`PyEval_AcquireLock` and :c:func:`PyEval_AcquireThread`
now terminate the current thread if called while the interpreter is
finalizing, making them consistent with :c:func:`PyEval_RestoreThread`,
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`.

- bpo-36504: Fix signed integer overflow in _ctypes.c's
``PyCArrayType_new()``.

- bpo-20844: Fix running script with encoding cookie and LF line ending may
fail on Windows.

- bpo-24214: Fixed support of the surrogatepass error handler in the UTF-8
incremental decoder.

- bpo-36452: Changing ``dict`` keys during iteration of the dict itself,
``keys()``, ``values()``, or ``items()`` will now be detected in certain
corner cases where keys are deleted/added so that the number of keys isn't
changed. A `RuntimeError` will be raised after ``len(dict)`` iterations.
Contributed by Thomas Perl.

- bpo-36459: Fix a possible double ``PyMem_FREE()`` due to tokenizer.c's
``tok_nextc()``.

- bpo-36433: Fixed TypeError message in classmethoddescr_call.

- bpo-36430: Fix a possible reference leak in :func:`itertools.count`.

- bpo-36440: Include node names in ``ParserError`` messages, instead of
numeric IDs. Patch by A. Skrobov.

- bpo-36143: Regenerate :mod:`keyword` from the Grammar and Tokens file
using pgen. Patch by Pablo Galindo.

- bpo-18372: Add missing :c:func:`PyObject_GC_Track` calls in the
:mod:`pickle` module. Patch by Zackery Spytz.

Library
-------

- bpo-35952: Fix pythoninfo when the compiler is missing.

- bpo-28238: The ``.find*()`` methods of xml.etree.ElementTree can now
search for wildcards like ``{*}tag`` and ``{ns}*`` that match a tag in any
namespace or all tags in a namespace. Patch by Stefan Behnel.

- bpo-26978: `pathlib.path.link_to()` is now implemented. It creates a hard
link pointing to a path.

- bpo-1613500: :class:`fileinput.FileInput` now uses the input file mode to
correctly set the output file mode (previously it was hardcoded to
``'w'``) when ``inplace=True`` is passed to its constructor.

- bpo-36734: Fix compilation of ``faulthandler.c`` on HP-UX. Initialize
``stack_t current_stack`` to zero using ``memset()``.

- bpo-13611: The xml.etree.ElementTree packages gained support for C14N 2.0
serialisation. Patch by Stefan Behnel.

- bpo-36669: Add missing matrix multiplication operator support to
weakref.proxy.

- bpo-36676: The XMLParser() in xml.etree.ElementTree provides namespace
prefix context to the parser target if it defines the callback methods
"start_ns()" and/or "end_ns()". Patch by Stefan Behnel.

- bpo-36673: The TreeBuilder and XMLPullParser in xml.etree.ElementTree
gained support for parsing comments and processing instructions. Patch by
Stefan Behnel.

- bpo-36650: The C version of functools.lru_cache() was treating calls with
an empty ``**kwargs`` dictionary as being distinct from calls with no
keywords at all. This did not result in an incorrect answer, but it did
trigger an unexpected cache miss.

- bpo-28552: Fix :mod:`distutils.sysconfig` if :data:`sys.executable` is
``None`` or an empty string: use :func:`os.getcwd` to initialize
``project_base``. Fix also the distutils build command: don't use
:data:`sys.executable` if it is ``None`` or an empty string.

- bpo-35755: :func:`shutil.which` and
:func:`distutils.spawn.find_executable` now use ``os.confstr("CS_PATH")``
if available instead of :data:`os.defpath`, if the ``PATH`` environment
variable is not set. Moreover, don't use ``os.confstr("CS_PATH")`` nor
:data:`os.defpath` if the ``PATH`` environment variable is set to an empty
string.

- bpo-25430: improve performance of ``IPNetwork.__contains__()``

- bpo-30485: Path expressions in xml.etree.ElementTree can now avoid
explicit namespace prefixes for tags (or the "{namespace}tag" notation) by
passing a default namespace with an empty string prefix.

- bpo-36613: Fix :mod:`asyncio` wait() not removing callback if exception

- bpo-36598: Fix ``isinstance`` check for Mock objects with spec when the
code is executed under tracing. Patch by Karthikeyan Singaravelan.

- bpo-18748: In development mode (:option:`-X` ``dev``) and in debug build,
the :class:`io.IOBase` destructor now logs ``close()`` exceptions. These
exceptions are silent by default in release mode.

- bpo-36575: The ``_lsprof`` module now uses internal timer same to
``time.perf_counter()`` by default. ``gettimeofday(2)`` was used on Unix.
New timer has better resolution on most Unix platforms and timings are no
longer impacted by system clock updates since ``perf_counter()`` is
monotonic. Patch by Inada Naoki.

- bpo-33461: ``json.loads`` now emits ``DeprecationWarning`` when
``encoding`` option is specified. Patch by Matthias Bussonnier.

- bpo-36559: The random module now prefers the lean internal _sha512 module
over hashlib for seed(version=2) to optimize import time.

- bpo-17561: Set backlog=None as the default for socket.create_server.

- bpo-34373: Fix :func:`time.mktime` error handling on AIX for year before
1970.

- bpo-36232: Improve error message when trying to open existing DBM database
that actually doesn't exist. Patch by Marco Rougeth.

- bpo-36546: Add statistics.quantiles()

- bpo-36050: Optimized ``http.client.HTTPResponse.read()`` for large
response. Patch by Inada Naoki.

- bpo-36522: If *debuglevel* is set to >0 in :mod:`http.client`, print all
values for headers with multiple values for the same header name. Patch by
Matt Houglum.

- bpo-36492: Deprecated passing required arguments like *func* as keyword
arguments in functions which should accept arbitrary keyword arguments and
pass them to other function. Arbitrary keyword arguments (even with names
"self" and "func") can now be passed to these functions if the required
arguments are passed as positional arguments.

- bpo-27181: Add statistics.geometric_mean().

- bpo-30427: ``os.path.normcase()`` relies on ``os.fspath()`` to check the
type of its argument. Redundant checks have been removed from its
``posixpath.normcase()`` and ``ntpath.normcase()`` implementations. Patch
by Wolfgang Maier.

- bpo-36385: Stop rejecting IPv4 octets for being ambiguously octal. Leading
zeros are ignored, and no longer are assumed to specify octal octets.
Octets are always decimal numbers. Octets must still be no more than three
digits, including leading zeroes.

- bpo-36434: Errors during writing to a ZIP file no longer prevent to
properly close it.

- bpo-36407: Fixed wrong indentation writing for CDATA section in
xml.dom.minidom. Patch by Vladimir Surjaninov.

- bpo-36326: inspect.getdoc() can now find docstrings for member objects
when __slots__ is a dictionary.

- bpo-36366: Calling ``stop()`` on an unstarted or stopped
:func:`unittest.mock.patch` object will now return `None` instead of
raising :exc:`RuntimeError`, making the method idempotent. Patch by
Karthikeyan Singaravelan.

- bpo-36348: The :meth:`imap.IMAP4.logout` method no longer ignores silently
arbitrary exceptions.

- bpo-31904: Add time module support and fix test_time faiures for VxWorks.

- bpo-36227: Added support for keyword arguments `default_namespace` and
`xml_declaration` in functions ElementTree.tostring() and
ElementTree.tostringlist().

- bpo-36004: Added new alternate constructors
:meth:`datetime.date.fromisocalendar` and
:meth:`datetime.datetime.fromisocalendar`, which construct date objects
from ISO year, week number and weekday; these are the inverse of each
class's ``isocalendar`` method. Patch by Paul Ganssle.

- bpo-35936: :mod:`modulefinder` no longer depends on the deprecated
:mod:`imp` module, and the initializer for
:class:`modulefinder.ModuleFinder` now has immutable default arguments.
Patch by Brandt Bucher.

- bpo-35376: :mod:`modulefinder` correctly handles modules that have the
same name as a bad package. Patch by Brandt Bucher.

- bpo-17396: :mod:`modulefinder` no longer crashes when encountering syntax
errors in followed imports. Patch by Brandt Bucher.

- bpo-35934: Added :meth:`~socket.create_server()` and
:meth:`~socket.has_dualstack_ipv6()` convenience functions to automate the
necessary tasks usually involved when creating a server socket, including
accepting both IPv4 and IPv6 connections on the same socket. (Contributed
by Giampaolo Rodola in :issue:`17561`.)

- bpo-23078: Add support for :func:`classmethod` and :func:`staticmethod` to
:func:`unittest.mock.create_autospec`. Initial patch by Felipe Ochoa.

- bpo-35416: Fix potential resource warnings in distutils. Patch by Mickaël
Schoentgen.

- bpo-25451: Add transparency methods to :class:`tkinter.PhotoImage`. Patch
by Zackery Spytz.

- bpo-35082: Don't return deleted attributes when calling dir on a
:class:`unittest.mock.Mock`.

- bpo-34547: :class:`wsgiref.handlers.BaseHandler` now handles abrupt client
connection terminations gracefully. Patch by Petter Strandmark.

- bpo-31658: :func:`xml.sax.parse` now supports :term:`path-like <path-like
object>`. Patch by Mickaël Schoentgen.

- bpo-34139: Remove stale unix datagram socket before binding

- bpo-33530: Implemented Happy Eyeballs in `asyncio.create_connection()`.
Added two new arguments, *happy_eyeballs_delay* and *interleave*, to
specify Happy Eyeballs behavior.

- bpo-33291: Do not raise AttributeError when calling the inspect functions
isgeneratorfunction, iscoroutinefunction, isasyncgenfunction on a method
created from an arbitrary callable. Instead, return False.

- bpo-31310: Fix the multiprocessing.semaphore_tracker so it is reused by
child processes

- bpo-31292: Fix ``setup.py check --restructuredtext`` for files containing
``include`` directives.

Documentation
-------------

- bpo-36625: Remove obsolete comments from docstrings in fractions.Fraction

- bpo-30840: Document relative imports

- bpo-36523: Add docstring for io.IOBase.writelines().

- bpo-36425: New documentation translation: `Simplified Chinese
<https://docs.python.org/zh-cn/>`_.

- bpo-36345: Avoid the duplication of code from ``Tools/scripts/serve.py``
in using the :rst:dir:`literalinclude` directive for the basic
wsgiref-based web server in the documentation of :mod:`wsgiref`.
Contributed by Stéphane Wirtel.

- bpo-36345: Using the code of the ``Tools/scripts/serve.py`` script as an
example in the :mod:`wsgiref` documentation. Contributed by Stéphane
Wirtel.

- bpo-36157: Added Documention for PyInterpreterState_Main().

- bpo-33043: Updates the docs.python.org page with the addition of a
'Contributing to Docs' link at the end of the page (between 'Reporting
Bugs' and 'About Documentation'). Updates the 'Found a Bug' page with
additional links and information in the Documentation Bugs section.

- bpo-35581: @typing.type_check_only now allows type stubs to mark functions
and classes not available during runtime.

- bpo-33832: Add glossary entry for 'magic method'.

- bpo-32913: Added re.Match.groupdict example to regex HOWTO.

Tests
-----

- bpo-36719: regrtest now always detects uncollectable objects. Previously,
the check was only enabled by ``--findleaks``. The check now also works
with ``-jN/--multiprocess N``. ``--findleaks`` becomes a deprecated alias
to ``--fail-env-changed``.

- bpo-36725: When using multiprocessing mode (-jN), regrtest now better
reports errors if a worker process fails, and it exits immediately on a
worker thread failure or when interrupted.

- bpo-36454: Change test_time.test_monotonic() to test only the lower bound
of elapsed time after a sleep command rather than the upper bound. This
prevents unnecessary test failures on slow buildbots. Patch by Victor
Stinner.

- bpo-32424: Improve test coverage for xml.etree.ElementTree. Patch by
Gordon P. Hemsley.

- bpo-32424: Fix typo in test_cyclic_gc() test for xml.etree.ElementTree.
Patch by Gordon P. Hemsley.

- bpo-36635: Add a new :mod:`_testinternalcapi` module to test the internal
C API.

- bpo-36629: Fix ``test_imap4_host_default_value()`` of ``test_imaplib``:
catch also :data:`errno.ENETUNREACH` error.

- bpo-36611: Fix ``test_sys.test_getallocatedblocks()`` when
:mod:`tracemalloc` is enabled.

- bpo-36560: Fix reference leak hunting in regrtest: compute also deltas (of
reference count, allocated memory blocks, file descriptor count) during
warmup, to ensure that everything is initialized before starting to hunt
reference leaks.

- bpo-36565: Fix reference hunting (``python3 -m test -R 3:3``) when Python
has no built-in abc module.

- bpo-31904: Port test_resource to VxWorks: skip tests cases setting
RLIMIT_FSIZE and RLIMIT_CPU.

- bpo-31904: Fix test_tabnanny on VxWorks: adjust ENOENT error message.

- bpo-36436: Fix ``_testcapi.pymem_buffer_overflow()``: handle memory
allocation failure.

- bpo-31904: Fix test_utf8_mode on VxWorks: Python always use UTF-8 on
VxWorks.

- bpo-36341: Fix tests that may fail with PermissionError upon calling
bind() on AF_UNIX sockets.

Build
-----

- bpo-36747: Remove the stale scriptsinstall Makefile target.

- bpo-21536: On Unix, C extensions are no longer linked to libpython except
on Android and Cygwin.

It is now possible for a statically linked Python to load a C extension
built using a shared library Python.

When Python is embedded, ``libpython`` must not be loaded with
``RTLD_LOCAL``, but ``RTLD_GLOBAL`` instead. Previously, using
``RTLD_LOCAL``, it was already not possible to load C extensions which
were not linked to ``libpython``, such as C extensions of the standard
library built by the ``*shared*`` section of ``Modules/Setup``.

distutils, python-config and python-config.py have been modified.

- bpo-36707: ``./configure --with-pymalloc`` no longer adds the ``m`` flag
to SOABI (sys.implementation.cache_tag). Enabling or disabling pymalloc
has no impact on the ABI.

- bpo-36635: Change ``PyAPI_FUNC(type)``, ``PyAPI_DATA(type)`` and
``PyMODINIT_FUNC`` macros of ``pyport.h`` when ``Py_BUILD_CORE_MODULE`` is
defined. The ``Py_BUILD_CORE_MODULE`` define must be now be used to build
a C extension as a dynamic library accessing Python internals: export the
PyInit_xxx() function in DLL exports on Windows.

- bpo-31904: Don't build the ``_crypt`` extension on VxWorks.

- bpo-36618: Add ``-fmax-type-align=8`` to CFLAGS when clang compiler is
detected. The pymalloc memory allocator aligns memory on 8 bytes. On
x86-64, clang expects alignment on 16 bytes by default and so uses MOVAPS
instruction which can lead to segmentation fault. Instruct clang that
Python is limited to alignment on 8 bytes to use MOVUPS instruction
instead: slower but don't trigger a SIGSEGV if the memory is not aligned
on 16 bytes. Sadly, the flag must be added to ``CFLAGS`` and not just
``CFLAGS_NODIST``, since third party C extensions can have the same issue.

- bpo-36605: ``make tags`` and ``make TAGS`` now also parse
``Modules/_io/*.c`` and ``Modules/_io/*.h``.

- bpo-36465: Release builds and debug builds are now ABI compatible:
defining the ``Py_DEBUG`` macro no longer implies the ``Py_TRACE_REFS``
macro, which introduces the only ABI incompatibility. The
``Py_TRACE_REFS`` macro, which adds the :func:`sys.getobjects` function
and the :envvar:`PYTHONDUMPREFS` environment variable, can be set using
the new ``./configure --with-trace-refs`` build option.

- bpo-36577: setup.py now correctly reports missing OpenSSL headers and
libraries again.

- bpo-36544: Fix regression introduced in bpo-36146 refactoring setup.py

- bpo-36508: ``python-config --ldflags`` no longer includes flags of the
``LINKFORSHARED`` variable. The ``LINKFORSHARED`` variable must only be
used to build executables.

- bpo-36503: Remove references to "aix3" and "aix4". Patch by M. Felt.

Windows
-------

- bpo-35920: Added platform.win32_edition() and platform.win32_is_iot().
Added support for cross-compiling packages for Windows ARM32. Skip tests
that are not expected to work on Windows IoT Core ARM32.

- bpo-36649: Remove trailing spaces for registry keys when installed via the
Store.

- bpo-34144: Fixed activate.bat to correctly update codepage when chcp.com
returns dots in output. Patch by Lorenz Mende.

- bpo-36509: Added preset-iot layout for Windows IoT ARM containers. This
layout doesn't contain UI components like tkinter or IDLE. It also doesn't
contain files to support on-target builds since Windows ARM32 builds must
be cross-compiled when using MSVC.

- bpo-35941: enum_certificates function of the ssl module now returns
certificates from all available certificate stores inside windows in a
query instead of returning only certificates from the system wide
certificate store. This includes certificates from these certificate
stores: local machine, local machine enterprise, local machine group
policy, current user, current user group policy, services, users.
ssl.enum_crls() function is changed in the same way to return all
certificate revocation lists inside the windows certificate revocation
list stores.

- bpo-36441: Fixes creating a venv when debug binaries are installed.

- bpo-36085: Enable better DLL resolution on Windows by using safe DLL
search paths and adding :func:`os.add_dll_directory`.

- bpo-36010: Add the venv standard library module to the nuget distribution
for Windows.

- bpo-29515: Add the following socket module constants on Windows:
IPPROTO_AH IPPROTO_CBT IPPROTO_DSTOPTS IPPROTO_EGP IPPROTO_ESP
IPPROTO_FRAGMENT IPPROTO_GGP IPPROTO_HOPOPTS IPPROTO_ICLFXBM
IPPROTO_ICMPV6 IPPROTO_IDP IPPROTO_IGMP IPPROTO_IGP IPPROTO_IPV4
IPPROTO_IPV6 IPPROTO_L2TP IPPROTO_MAX IPPROTO_ND IPPROTO_NONE IPPROTO_PGM
IPPROTO_PIM IPPROTO_PUP IPPROTO_RDP IPPROTO_ROUTING IPPROTO_SCTP
IPPROTO_ST

- bpo-35947: Added current version of libffi to cpython-source-deps. Change
_ctypes to use current version of libffi on Windows.

- bpo-34060: Report system load when running test suite on Windows. Patch by
Ammar Askar. Based on prior work by Jeremy Kloth.

- bpo-31512: With the Windows 10 Creators Update, non-elevated users can now
create symlinks as long as the computer has Developer Mode enabled.

macOS
-----

- bpo-34602: Avoid failures setting macOS stack resource limit with
resource.setrlimit. This reverts an earlier fix for bpo-18075 which forced
a non-default stack size when building the interpreter executable on
macOS.

IDLE
----

- bpo-36429: Fix starting IDLE with pyshell. Add idlelib.pyshell alias at
top; remove pyshell alias at bottom. Remove obsolete __name__=='__main__'
command.

Tools/Demos
-----------

- bpo-14546: Fix the argument handling in Tools/scripts/lll.py.

C API
-----

- bpo-36763: Fix memory leak in :c:func:`Py_SetStandardStreamEncoding`:
release memory if the function is called twice.

- bpo-36641: :c:expr:`PyDoc_VAR(name)` and :c:expr:`PyDoc_STRVAR(name,str)`
now create ``static const char name[]`` instead of ``static char name[]``.
Patch by Inada Naoki.

- bpo-36389: Change the value of ``CLEANBYTE``, ``DEADDYTE`` and
``FORBIDDENBYTE`` internal constants used by debug hooks on Python memory
allocators (:c:func:`PyMem_SetupDebugHooks` function). Byte patterns
``0xCB``, ``0xDB`` and ``0xFB`` have been replaced with ``0xCD``, ``0xDD``
and ``0xFD`` to use the same values than Windows CRT debug ``malloc()``
and ``free()``.

- bpo-36443: Since Python 3.7.0, calling :c:func:`Py_DecodeLocale` before
:c:func:`Py_Initialize` produces mojibake if the ``LC_CTYPE`` locale is
coerced and/or if the UTF-8 Mode is enabled by the user configuration. The
LC_CTYPE coercion and UTF-8 Mode are now disabled by default to fix the
mojibake issue. They must now be enabled explicitly (opt-in) using the new
:c:func:`_Py_PreInitialize` API with ``_PyPreConfig``.

- bpo-36025: Fixed an accidental change to the datetime C API where the
arguments to the :c:func:`PyDate_FromTimestamp` function were incorrectly
interpreted as a single timestamp rather than an arguments tuple, which
causes existing code to start raising :exc:`TypeError`. The
backwards-incompatible change was only present in alpha releases of Python
3.8. Patch by Paul Ganssle.

- bpo-35810: Modify ``PyObject_Init`` to correctly increase the refcount of
heap- allocated Type objects. Also fix the refcounts of the heap-allocated
types that were either doing this manually or not decreasing the type's
refcount in tp_dealloc

What's New in Python 3.8.0 alpha 3?
===================================

*Release date: 2019-03-25*

Security
--------

- bpo-36216: Changes urlsplit() to raise ValueError when the URL contains
characters that decompose under IDNA encoding (NFKC-normalization) into
characters that affect how the URL is parsed.

- bpo-35121: Don't send cookies of domain A without Domain attribute to
domain B when domain A is a suffix match of domain B while using a
cookiejar with :class:`http.cookiejar.DefaultCookiePolicy` policy. Patch
by Karthikeyan Singaravelan.

Core and Builtins
-----------------

- bpo-36421: Fix a possible double decref in _ctypes.c's
``PyCArrayType_new()``.

- bpo-36412: Fix a possible crash when creating a new dictionary.

- bpo-36398: Fix a possible crash in ``structseq_repr()``.

- bpo-36256: Fix bug in parsermodule when parsing a state in a DFA that has
two or more arcs with labels of the same type. Patch by Pablo Galindo.

- bpo-36365: repr(structseq) is no longer limited to 512 bytes.

- bpo-36374: Fix a possible null pointer dereference in
``merge_consts_recursive()``. Patch by Zackery Spytz.

- bpo-36236: At Python initialization, the current directory is no longer
prepended to :data:`sys.path` if it has been removed.

- bpo-36352: Python initialization now fails with an error, rather than
silently truncating paths, if a path is too long.

- bpo-36301: Python initialization now fails if decoding ``pybuilddir.txt``
configuration file fails at startup.

- bpo-36333: Fix leak in _PyRuntimeState_Fini. Contributed by Stéphane
Wirtel.

- bpo-36332: The builtin :func:`compile` can now handle AST objects that
contain assignment expressions. Patch by Pablo Galindo.

- bpo-36282: Improved error message for too much positional arguments in
some builtin functions.

- bpo-30040: New empty dict uses fewer memory for now. It used more memory
than empty dict created by ``dict.clear()``. And empty dict creation and
deletion is about 2x faster. Patch by Inada Naoki.

- bpo-36262: Fix an unlikely memory leak on conversion from string to float
in the function ``_Py_dg_strtod()`` used by ``float(str)``,
``complex(str)``, :func:`pickle.load`, :func:`marshal.load`, etc.

- bpo-36252: Update Unicode databases to version 12.0.0.

- bpo-36218: Fix a segfault occurring when sorting a list of heterogeneous
values. Patch contributed by Rémi Lapeyre and Elliot Gorokhovsky.

- bpo-36188: Cleaned up left-over vestiges of Python 2 unbound method
handling in method objects and documentation. Patch by Martijn Pieters

- bpo-36124: Add a new interpreter-specific dict and expose it in the C-API
via PyInterpreterState_GetDict(). This parallels PyThreadState_GetDict().
However, extension modules should continue using PyModule_GetState() for
their own internal per-interpreter state.

- bpo-35975: Add a ``feature_version`` flag to ``ast.parse()`` (documented)
and ``compile()`` (hidden) that allows tweaking the parser to support
older versions of the grammar. In particular, if ``feature_version`` is 5
or 6, the hacks for the ``async`` and ``await`` keyword from PEP 492 are
reinstated. (For 7 or higher, these are unconditionally treated as
keywords, but they are still special tokens rather than ``NAME`` tokens
that the parser driver recognizes.)

- bpo-31904: Use UTF-8 as the system encoding on VxWorks.

- bpo-36048: The :meth:`~object.__index__` special method will be used
instead of :meth:`~object.__int__` for implicit conversion of Python
numbers to C integers. Using the ``__int__()`` method in implicit
conversions has been deprecated.

- bpo-35808: Retire pgen and use a modified version of pgen2 to generate the
parser. Patch by Pablo Galindo.

Library
-------

- bpo-36401: The class documentation created by pydoc now has a separate
section for readonly properties.

- bpo-36320: The typing.NamedTuple() class has deprecated the _field_types
attribute in favor of the __annotations__ attribute which carried the same
information. Also, both attributes were converted from OrderedDict to a
regular dict.

- bpo-34745: Fix :mod:`asyncio` ssl memory issues caused by circular
references

- bpo-36324: Add method to statistics.NormalDist for computing the inverse
cumulative normal distribution.

- bpo-36321: collections.namedtuple() misspelled the name of an attribute.
To be consistent with typing.NamedTuple, the attribute name should have
been "_field_defaults" instead of "_fields_defaults". For backwards
compatibility, both spellings are now created. The misspelled version may
be removed in the future.

- bpo-36297: "unicode_internal" codec is removed. It was deprecated since
Python 3.3. Patch by Inada Naoki.

- bpo-36298: Raise ModuleNotFoundError in pyclbr when a module can't be
found. Thanks to 'mental' for the bug report.

- bpo-36268: Switch the default format used for writing tars with
mod:`tarfile` to the modern POSIX.1-2001 pax standard, from the
vendor-specific GNU. Contributed by C.A.M. Gerlach.

- bpo-36285: Fix integer overflows in the array module. Patch by Stephan
Hohe.

- bpo-31904: Add _signal module support for VxWorks.

- bpo-36272: :mod:`logging` does not silently ignore RecursionError anymore.
Patch contributed by Rémi Lapeyre.

- bpo-36280: Add a kind field to ast.Constant. It is 'u' if the literal has
a 'u' prefix (i.e. a Python 2 style unicode literal), else None.

- bpo-35931: The :mod:`pdb` ``debug`` command now gracefully handles all
exceptions.

- bpo-36251: Fix format strings used for stderrprinter and re.Match reprs.
Patch by Stephan Hohe.

- bpo-36235: Fix ``CFLAGS`` in ``customize_compiler()`` of
``distutils.sysconfig``: when the ``CFLAGS`` environment variable is
defined, don't override ``CFLAGS`` variable with the ``OPT`` variable
anymore. Initial patch written by David Malcolm.

- bpo-35807: Update ensurepip to install pip 19.0.3 and setuptools 40.8.0.

- bpo-36139: Release GIL when closing :class:`~mmap.mmap` objects.

- bpo-36179: Fix two unlikely reference leaks in _hashopenssl. The leaks
only occur in out-of-memory cases.

- bpo-36169: Add overlap() method to statistics.NormalDist. Computes the
overlapping coefficient for two normal distributions.

- bpo-36103: Default buffer size used by ``shutil.copyfileobj()`` is changed
from 16 KiB to 64 KiB on non-Windows platform to reduce system call
overhead. Contributed by Inada Naoki.

- bpo-36130: Fix ``pdb`` with ``skip=...`` when stepping into a frame
without a ``__name__`` global. Patch by Anthony Sottile.

- bpo-35652: shutil.copytree(copy_function=...) erroneously pass DirEntry
instead of a path string.

- bpo-35178: Ensure custom :func:`warnings.formatwarning` function can
receive `line` as positional argument. Based on patch by Tashrif Billah.

- bpo-36106: Resolve potential name clash with libm's sinpi(). Patch by
Dmitrii Pasechnik.

- bpo-36091: Clean up reference to async generator in Lib/types. Patch by
Henry Chen.

- bpo-36043: :class:`FileCookieJar` supports :term:`path-like object`.
Contributed by Stéphane Wirtel

- bpo-35899: Enum has been fixed to correctly handle empty strings and
strings with non-Latin characters (ie. 'α', '×�') without crashing.
Original patch contributed by Maxwell. Assisted by Stéphane Wirtel.

- bpo-21269: Add ``args`` and ``kwargs`` properties to mock call objects.
Contributed by Kumar Akshay.

- bpo-30670: `pprint.pp` has been added to pretty-print objects with
dictionary keys being sorted with their insertion order by default.
Parameter *sort_dicts* has been added to `pprint.pprint`, `pprint.pformat`
and `pprint.PrettyPrinter`. Contributed by Rémi Lapeyre.

- bpo-35843: Implement ``__getitem__`` for ``_NamespacePath``. Patch by
Anthony Sottile.

- bpo-35802: Clean up code which checked presence of ``os.stat`` /
``os.lstat`` / ``os.chmod`` which are always present. Patch by Anthony
Sottile.

- bpo-35715: Librates the return value of a ProcessPoolExecutor
_process_worker after it's no longer needed to free memory

- bpo-35493: Use :func:`multiprocessing.connection.wait` instead of polling
each 0.2 seconds for worker updates in :class:`multiprocessing.Pool`.
Patch by Pablo Galindo.

- bpo-35661: Store the venv prompt in pyvenv.cfg.

- bpo-35121: Don't set cookie for a request when the request path is a
prefix match of the cookie's path attribute but doesn't end with "/".
Patch by Karthikeyan Singaravelan.

- bpo-21478: Calls to a child function created with
:func:`unittest.mock.create_autospec` should propagate to the parent.
Patch by Karthikeyan Singaravelan.

- bpo-35198: Fix C++ extension compilation on AIX

Documentation
-------------

- bpo-36329: Declare the path of the Python binary for the usage of
``Tools/scripts/serve.py`` when executing ``make -C Doc/ serve``.
Contributed by Stéphane Wirtel

- bpo-36138: Improve documentation about converting datetime.timedelta to
scalars.

- bpo-21314: A new entry was added to the Core Language Section of the
Programming FAQ, which explaines the usage of slash(/) in the signature of
a function. Patch by Lysandros Nikolaou

Tests
-----

- bpo-36234: test_posix.PosixUidGidTests: add tests for invalid uid/gid type
(str). Initial patch written by David Malcolm.

- bpo-29571: Fix ``test_re.test_locale_flag()``: use
``locale.getpreferredencoding()`` rather than ``locale.getlocale()`` to
get the locale encoding. With some locales, ``locale.getlocale()`` returns
the wrong encoding.

- bpo-36123: Fix race condition in test_socket.

Build
-----

- bpo-36356: Fix leaks that led to build failure when configured with
address sanitizer.

- bpo-36146: Add ``TEST_EXTENSIONS`` constant to ``setup.py`` to allow to
not build test extensions like ``_testcapi``.

- bpo-36146: Fix setup.py on macOS: only add ``/usr/include/ffi`` to include
directories of _ctypes, not for all extensions.

- bpo-31904: Enable build system to cross-build for VxWorks RTOS.

Windows
-------

- bpo-36312: Fixed decoders for the following code pages: 50220, 50221,
50222, 50225, 50227, 50229, 57002 through 57011, 65000 and 42.

- bpo-36264: Don't honor POSIX ``HOME`` in ``os.path.expanduser`` on
windows. Patch by Anthony Sottile.

- bpo-24643: Fix name collisions due to ``#define timezone _timezone`` in
PC/pyconfig.h.

IDLE
----

- bpo-36405: Use dict unpacking in idlelib.

- bpo-36396: Remove fgBg param of idlelib.config.GetHighlight(). This param
was only used twice and changed the return type.

- bpo-36176: Fix IDLE autocomplete & calltip popup colors. Prevent conflicts
with Linux dark themes (and slightly darken calltip background).

- bpo-23205: For the grep module, add tests for findfiles, refactor
findfiles to be a module-level function, and refactor findfiles to use
os.walk.

- bpo-23216: Add docstrings to IDLE search modules.

- bpo-36152: Remove colorizer.ColorDelegator.close_when_done and the
corresponding argument of .close(). In IDLE, both have always been None
or False since 2007.

- bpo-32129: Avoid blurry IDLE application icon on macOS with Tk 8.6. Patch
by Kevin Walzer.

- bpo-36096: Refactor class variables to instance variables in colorizer.

- bpo-30348: Increase test coverage of idlelib.autocomplete by 30%. Patch by
Louie Lu

Tools/Demos
-----------

- bpo-35132: Fix py-list and py-bt commands of python-gdb.py on gdb7.

- bpo-32217: Fix freeze script on Windows.

C API
-----

- bpo-36381: Raise ``DeprecationWarning`` when '#' formats are used for
building or parsing values without ``PY_SSIZE_T_CLEAN``.

- bpo-36142: The whole coreconfig.h header is now excluded from
Py_LIMITED_API. Move functions definitions into a new internal
pycore_coreconfig.h header.

What's New in Python 3.8.0 alpha 2?
===================================

*Release date: 2019-02-25*

Core and Builtins
-----------------

- bpo-36052: Raise a :exc:`SyntaxError` when assigning a value to
`__debug__` with the Assignment Operator. Contributed by Stéphane Wirtel
and Pablo Galindo.

- bpo-36012: Doubled the speed of class variable writes. When a non-dunder
attribute was updated, there was an unnecessary call to update slots.

- bpo-35942: The error message emitted when returning invalid types from
``__fspath__`` in interfaces that allow passing :class:`~os.PathLike`
objects has been improved and now it does explain the origin of the error.

- bpo-36016: ``gc.get_objects`` can now receive an optional parameter
indicating a generation to get objects from. Patch by Pablo Galindo.

- bpo-1054041: When the main interpreter exits due to an uncaught
KeyboardInterrupt, the process now exits in the appropriate manner for its
parent process to detect that a SIGINT or ^C terminated the process. This
allows shells and batch scripts to understand that the user has asked them
to stop.

- bpo-35992: Fix ``__class_getitem__()`` not being called on a class with a
custom non-subscriptable metaclass.

- bpo-35993: Fix a crash on fork when using subinterpreters. Contributed by
Stéphane Wirtel

- bpo-35991: Fix a potential double free in Modules/_randommodule.c.

- bpo-35961: Fix a crash in slice_richcompare(): use strong references
rather than stolen references for the two temporary internal tuples.

- bpo-35911: Enable the creation of cell objects by adding a
``cell.__new__`` method, and expose the type ``cell`` in ``Lib/types.py``
under the name CellType. Patch by Pierre Glaser.

- bpo-12822: Use monotonic clock for ``pthread_cond_timedwait`` when
``pthread_condattr_setclock`` and ``CLOCK_MONOTONIC`` are available.

- bpo-15248: The compiler emits now syntax warnings in the case when a comma
is likely missed before tuple or list.

- bpo-35886: The implementation of PyInterpreterState has been moved into
the internal header files (guarded by Py_BUILD_CORE).

- bpo-31506: Clarify the errors reported when ``object.__new__`` and
``object.__init__`` receive more than one argument. Contributed by Sanyam
Khurana.

- bpo-35724: Signal-handling is now guaranteed to happen relative to the
main interpreter.

- bpo-33608: We added a new internal _Py_AddPendingCall() that operates
relative to the provided interpreter. This allows us to use the existing
implementation to ask another interpreter to do work that cannot be done
in the current interpreter, like decref an object the other interpreter
owns. The existing Py_AddPendingCall() only operates relative to the main
interpreter.

- bpo-33989: Fix a possible crash in :meth:`list.sort` when sorting objects
with ``ob_type->tp_richcompare == NULL``. Patch by Zackery Spytz.

Library
-------

- bpo-35512: :func:`unittest.mock.patch.dict` used as a decorator with
string target resolves the target during function call instead of during
decorator construction. Patch by Karthikeyan Singaravelan.

- bpo-36018: Add statistics.NormalDist, a tool for creating and manipulating
normal distributions of random variable. Features a composite class that
treats the mean and standard deviation of measurement data as single
entity.

- bpo-35904: Added statistics.fmean() as a faster, floating point variant of
the existing mean() function.

- bpo-35918: Removed broken ``has_key`` method from
multiprocessing.managers.SyncManager.dict. Contributed by Rémi Lapeyre.

- bpo-18283: Add support for bytes to :func:`shutil.which`.

- bpo-35960: Fix :func:`dataclasses.field` throwing away empty mapping
objects passed as metadata.

- bpo-35500: Write expected and actual call parameters on separate lines in
:meth:`unittest.mock.Mock.assert_called_with` assertion errors.
Contributed by Susan Su.

- bpo-35931: The :mod:`pdb` ``debug`` command now gracefully handles syntax
errors.

- bpo-24209: In http.server script, rely on getaddrinfo to bind to preferred
address based on the bind parameter. Now default bind or binding to a name
may bind to IPv6 or dual-stack, depending on the environment.

- bpo-35321: Set ``__spec__.origin`` of ``_frozen_importlib`` to frozen so
that it matches the behavior of ``_frozen_importlib_external``. Patch by
Nina Zakharenko.

- bpo-35378: Fix a reference issue inside :class:`multiprocessing.Pool` that
caused the pool to remain alive if it was deleted without being closed or
terminated explicitly. A new strong reference is added to the pool
iterators to link the lifetime of the pool to the lifetime of its
iterators so the pool does not get destroyed if a pool iterator is still
alive.

- bpo-34294: re module, fix wrong capturing groups in rare cases.
:func:`re.search`, :func:`re.findall`, :func:`re.sub` and other functions
that scan through string looking for a match, should reset capturing
groups between two match attempts. Patch by Ma Lin.

- bpo-35615: :mod:`weakref`: Fix a RuntimeError when copying a
WeakKeyDictionary or a WeakValueDictionary, due to some keys or values
disappearing while iterating.

- bpo-35606: Implement :func:`math.prod` as analogous function to
:func:`sum` that returns the product of a 'start' value (default: 1) times
an iterable of numbers. Patch by Pablo Galindo.

- bpo-32417: Performing arithmetic between :class:`datetime.datetime`
subclasses and :class:`datetime.timedelta` now returns an object of the
same type as the :class:`datetime.datetime` subclass. As a result,
:meth:`datetime.datetime.astimezone` and alternate constructors like
:meth:`datetime.datetime.now` and :meth:`datetime.fromtimestamp` called
with a ``tz`` argument now *also* retain their subclass.

- bpo-35153: Add *headers* optional keyword-only parameter to
:class:`xmlrpc.client.ServerProxy`, :class:`xmlrpc.client.Transport` and
:class:`xmlrpc.client.SafeTransport`. Patch by Cédric Krier.

- bpo-34572: Fix C implementation of pickle.loads to use importlib's locking
mechanisms, and thereby avoid using partially loaded modules. Patch by Tim
Burgess.

Documentation
-------------

- bpo-36083: Fix formatting of --check-hash-based-pycs options in the
manpage Synopsis.

- bpo-36007: Bump minimum sphinx version to 1.8. Patch by Anthony Sottile.

- bpo-22062: Update documentation and docstrings for pathlib. Original patch
by Mike Short.

Tests
-----

- bpo-27313: Avoid test_ttk_guionly ComboboxTest failure with macOS Cocoa
Tk.

- bpo-36019: Add test.support.TEST_HTTP_URL and replace references of
http://www.example.com by this new constant. Contributed by Stéphane
Wirtel.

- bpo-36037: Fix test_ssl for strict OpenSSL configuration like RHEL8 strict
crypto policy. Use older TLS version for minimum TLS version of the server
SSL context if needed, to test TLS version older than default minimum TLS
version.

- bpo-35798: Added :func:`test.support.check_syntax_warning`.

- bpo-35505: Make test_imap4_host_default_value independent on whether the
local IMAP server is running.

- bpo-35917: multiprocessing: provide unit tests for SyncManager and
SharedMemoryManager classes + all the shareable types which are supposed
to be supported by them. (patch by Giampaolo Rodola)

- bpo-35704: Skip ``test_shutil.test_unpack_archive_xztar`` to prevent a
MemoryError on 32-bit AIX when MAXDATA setting is less than 0x20000000.

Patch by Michael Felt (aixtools)

- bpo-34720: Assert m_state != NULL to mimic GC traversal functions that do
not correctly handle module creation when the module state has not been
created.

Windows
-------

- bpo-35976: Added ARM build support to Windows build files in PCBuild.

- bpo-35692: ``pathlib`` no longer raises when checking file and directory
existence on drives that are not ready

- bpo-35872: Uses the base Python executable when invoking venv in a virtual
environment

- bpo-35873: Prevents venv paths being inherited by child processes

- bpo-35299: Fix sysconfig detection of the source directory and distutils
handling of pyconfig.h during PGO profiling

IDLE
----

- bpo-24310: IDLE -- Document settings dialog font tab sample.

- bpo-35833: Revise IDLE doc for control codes sent to Shell. Add a code
example block.

- bpo-35689: Add docstrings and unittests for colorizer.py.

What's New in Python 3.8.0 alpha 1?
===================================

*Release date: 2019-02-03*

Security
--------

- bpo-35746: [CVE-2019-5010] Fix a NULL pointer deref in ssl module. The
cert parser did not handle CRL distribution points with empty DP or URI
correctly. A malicious or buggy certificate can result into segfault.
Vulnerability (TALOS-2018-0758) reported by Colin Read and Nicolas Edet of
Cisco.

- bpo-34812: The :option:`-I` command line option (run Python in isolated
mode) is now also copied by the :mod:`multiprocessing` and
:mod:`distutils` modules when spawning child processes. Previously, only
:option:`-E` and :option:`-s` options (enabled by :option:`-I`) were
copied.

- bpo-34791: The xml.sax and xml.dom.domreg no longer use environment
variables to override parser implementations when
sys.flags.ignore_environment is set by -E or -I arguments.

- bpo-17239: The xml.sax and xml.dom.minidom parsers no longer processes
external entities by default. External DTD and ENTITY declarations no
longer load files or create network connections.

- bpo-34623: CVE-2018-14647: The C accelerated _elementtree module now
initializes hash randomization salt from _Py_HashSecret instead of
libexpat's default CSPRNG.

- bpo-34405: Updated to OpenSSL 1.1.0i for Windows builds.

- bpo-33871: Fixed sending the part of the file in :func:`os.sendfile` on
macOS. Using the *trailers* argument could cause sending more bytes from
the input file than was specified.

- bpo-32533: Fixed thread-safety of error handling in _ssl.

- bpo-33136: Harden ssl module against LibreSSL CVE-2018-8970.
X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new
test ensures that NULL bytes are not allowed.

- bpo-33001: Minimal fix to prevent buffer overrun in os.symlink on Windows

- bpo-32981: Regexes in difflib and poplib were vulnerable to catastrophic
backtracking. These regexes formed potential DOS vectors (REDOS). They
have been refactored. This resolves CVE-2018-1060 and CVE-2018-1061. Patch
by Jamie Davis.

- bpo-28414: The ssl module now allows users to perform their own IDN
en/decoding when using SNI.

Core and Builtins
-----------------

- bpo-35877: Make parenthesis optional for named expressions in while
statement. Patch by Karthikeyan Singaravelan.

- bpo-35814: Allow same right hand side expressions in annotated assignments
as in normal ones. In particular, ``x: Tuple[int, int] = 1, 2`` (without
parentheses on the right) is now allowed.

- bpo-35766: Add the option to parse PEP 484 type comments in the ast
module. (Off by default.) This is merging the key functionality of the
third party fork thereof,
[typed_ast](https://github.com/python/typed_ast).

- bpo-35713: Reorganize Python initialization to get working exceptions and
sys.stderr earlier.

- bpo-33416: Add end line and end column position information to the Python
AST nodes. This is a C-level backwards incompatible change.

- bpo-35720: Fixed a minor memory leak in pymain_parse_cmdline_impl function
in Modules/main.c

- bpo-35634: ``func(**kwargs)`` will now raise an error when ``kwargs`` is a
mapping containing multiple entries with the same key. An error was
already raised when other keyword arguments are passed before ``**kwargs``
since Python 3.6.

- bpo-35623: Fix a crash when sorting very long lists. Patch by Stephan
Hohe.

- bpo-35214: clang Memory Sanitizer build instrumentation was added to work
around false positives from posix, socket, time, test_io, and
test_faulthandler.

- bpo-35560: Fix an assertion error in :func:`format` in debug build for
floating point formatting with "n" format, zero padding and small width.
Release build is not impacted. Patch by Karthikeyan Singaravelan.

- bpo-35552: Format characters ``%s`` and ``%V`` in
:c:func:`PyUnicode_FromFormat` and ``%s`` in :c:func:`PyBytes_FromFormat`
no longer read memory past the limit if *precision* is specified.

- bpo-35504: Fix segfaults and :exc:`SystemError`\ s when deleting certain
attributes. Patch by Zackery Spytz.

- bpo-35504: Fixed a SystemError when delete the characters_written
attribute of an OSError.

- bpo-35494: Improved syntax error messages for unbalanced parentheses in
f-string.

- bpo-35444: Fixed error handling in pickling methods when fail to look up
builtin "getattr". Sped up pickling iterators.

- bpo-35436: Fix various issues with memory allocation error handling.
Patch by Zackery Spytz.

- bpo-35423: Separate the signal handling trigger in the eval loop from the
"pending calls" machinery. There is no semantic change and the difference
in performance is insignificant.

- bpo-35357: Internal attributes' names of unittest.mock._Call and
unittest.mock.MagicProxy (name, parent & from_kall) are now prefixed with
_mock_ in order to prevent clashes with widely used object attributes.
Fixed minor typo in test function name.

- bpo-35372: Fixed the code page decoder for input longer than 2 GiB
containing undecodable bytes.

- bpo-35336: Fix PYTHONCOERCECLOCALE=1 environment variable: only coerce the
C locale if the LC_CTYPE locale is "C".

- bpo-31241: The *lineno* and *col_offset* attributes of AST nodes for list
comprehensions, generator expressions and tuples are now point to the
opening parenthesis or square brace. For tuples without parenthesis they
point to the position of the first item.

- bpo-33954: For :meth:`str.format`, :meth:`float.__format__` and
:meth:`complex.__format__` methods for non-ASCII decimal point when using
the "n" formatter.

- bpo-35269: Fix a possible segfault involving a newly created coroutine.
Patch by Zackery Spytz.

- bpo-35224: Implement :pep:`572` (assignment expressions). Patch by Emily
Morehouse.

- bpo-32492: Speed up :class:`namedtuple` attribute access by 1.6x using a C
fast-path for the name descriptors. Patch by Pablo Galindo.

- bpo-35214: Fixed an out of bounds memory access when parsing a truncated
unicode escape sequence at the end of a string such as ``'\N'``. It would
read one byte beyond the end of the memory allocation.

- bpo-35214: The interpreter and extension modules have had annotations
added so that they work properly under clang's Memory Sanitizer. A new
configure flag --with-memory-sanitizer has been added to make test builds
of this nature easier to perform.

- bpo-35193: Fix an off by one error in the bytecode peephole optimizer
where it could read bytes beyond the end of bounds of an array when
removing unreachable code. This bug was present in every release of Python
3.6 and 3.7 until now.

- bpo-35169: Improved error messages for forbidden assignments.

- bpo-34022: Fix handling of hash-based bytecode files in :mod:`zipimport`.
Patch by Elvis Pranskevichus.

- bpo-28401: Debug builds will no longer to attempt to import extension
modules built for the ABI as they were never compatible to begin with.
Patch by Stefano Rivera.

- bpo-29341: Clarify in the docstrings of :mod:`os` methods that path-like
objects are also accepted as input parameters.

- bpo-35050: :mod:`socket`: Fix off-by-one bug in length check for
``AF_ALG`` name and type.

- bpo-29743: Raise :exc:`ValueError` instead of :exc:`OverflowError` in case
of a negative ``_length_`` in a :class:`ctypes.Array` subclass. Also
raise :exc:`TypeError` instead of :exc:`AttributeError` for non-integer
``_length_``. Original patch by Oren Milman.

- bpo-16806: Fix ``lineno`` and ``col_offset`` for multi-line string tokens.

- bpo-35029: :exc:`SyntaxWarning` raised as an exception at code generation
time will be now replaced with a :exc:`SyntaxError` for better error
reporting.

- bpo-34983: Expose :meth:`symtable.Symbol.is_nonlocal` in the symtable
module. Patch by Pablo Galindo.

- bpo-34974: :class:`bytes` and :class:`bytearray` constructors no longer
convert unexpected exceptions (e.g. :exc:`MemoryError` and
:exc:`KeyboardInterrupt`) to :exc:`TypeError`.

- bpo-34939: Allow annotated names in module namespace that are declared
global before the annotation happens. Patch by Pablo Galindo.

- bpo-34973: Fixed crash in :func:`bytes` when the :class:`list` argument is
mutated while it is iterated.

- bpo-34876: The *lineno* and *col_offset* attributes of the AST for
decorated function and class refer now to the position of the
corresponding ``def``, ``async def`` and ``class`` instead of the position
of the first decorator. This leads to more correct line reporting in
tracing. This is the only case when the position of child AST nodes can
precede the position of the parent AST node.

- bpo-34879: Fix a possible null pointer dereference in bytesobject.c.
Patch by Zackery Spytz.

- bpo-34784: Fix the implementation of PyStructSequence_NewType in order to
create heap allocated StructSequences.

- bpo-32912: A :exc:`SyntaxWarning` is now emitted instead of a
:exc:`DeprecationWarning` for invalid escape sequences in string and bytes
literals.

- bpo-34854: Fixed a crash in compiling string annotations containing a
lambda with a keyword-only argument that doesn't have a default value.

- bpo-34850: The compiler now produces a :exc:`SyntaxWarning` when identity
checks (``is`` and ``is not``) are used with certain types of literals
(e.g. strings, ints). These can often work by accident in CPython, but
are not guaranteed by the language spec. The warning advises users to use
equality tests (``==`` and ``!=``) instead.

- bpo-34824: Fix a possible null pointer dereference in Modules/_ssl.c.
Patch by Zackery Spytz.

- bpo-30156: The C function ``property_descr_get()`` uses a "cached" tuple
to optimize function calls. But this tuple can be discovered in debug mode
with :func:`sys.getobjects()`. Remove the optimization, it's not really
worth it and it causes 3 different crashes last years.

- bpo-34762: Fix contextvars C API to use PyObject* pointer types.

- bpo-34751: The hash function for tuples is now based on xxHash which gives
better collision results on (formerly) pathological cases. Additionally,
on 64-bit systems it improves tuple hashes in general. Patch by Jeroen
Demeyer with substantial contributions by Tim Peters.

- bpo-34735: Fix a memory leak in Modules/timemodule.c. Patch by Zackery
Spytz.

- bpo-34683: Fixed a bug where some SyntaxError error pointed to locations
that were off-by-one.

- bpo-34651: Only allow the main interpreter to fork. The avoids the
possibility of affecting the main interpreter, which is critical to
operation of the runtime.

- bpo-34653: Remove unused function PyParser_SimpleParseStringFilename.

- bpo-32236: Warn that line buffering is not supported if :func:`open` is
called with binary mode and ``buffering=1``.

- bpo-34641: Further restrict the syntax of the left-hand side of keyword
arguments in function calls. In particular, ``f((keyword)=arg)`` is now
disallowed.

- bpo-34637: Make the *start* argument to *sum()* visible as a keyword
argument.

- bpo-1621: Do not assume signed integer overflow behavior (C undefined
behavior) when performing set hash table resizing.

- bpo-34588: Fix an off-by-one in the recursive call pruning feature of
traceback formatting.

- bpo-34485: On Windows, the LC_CTYPE is now set to the user preferred
locale at startup. Previously, the LC_CTYPE locale was "C" at startup, but
changed when calling setlocale(LC_CTYPE, "") or setlocale(LC_ALL, "").

- bpo-34485: Standard streams like sys.stdout now use the "surrogateescape"
error handler, instead of "strict", on the POSIX locale (when the C locale
is not coerced and the UTF-8 Mode is disabled).

- bpo-34485: Fix the error handler of standard streams like sys.stdout:
PYTHONIOENCODING=":" is now ignored instead of setting the error handler
to "strict".

- bpo-34485: Python now gets the locale encoding with C code to initialize
the encoding of standard streams like sys.stdout. Moreover, the encoding
is now initialized to the Python codec name to get a normalized encoding
name and to ensure that the codec is loaded. The change avoids importing
_bootlocale and _locale modules at startup by default.

- bpo-34527: On FreeBSD, Py_DecodeLocale() and Py_EncodeLocale() now also
forces the ASCII encoding if the LC_CTYPE locale is "POSIX", not only if
the LC_CTYPE locale is "C".

- bpo-34527: The UTF-8 Mode is now also enabled by the "POSIX" locale, not
only by the "C" locale.

- bpo-34403: On HP-UX with C or POSIX locale, sys.getfilesystemencoding()
now returns "ascii" instead of "roman8" (when the UTF-8 Mode is disabled
and the C locale is not coerced).

- bpo-34523: The Python filesystem encoding is now read earlier during the
Python initialization.

- bpo-12458: Tracebacks show now correct line number for subexpressions in
multiline expressions. Tracebacks show now the line number of the first
line for multiline expressions instead of the line number of the last
subexpression.

- bpo-34408: Prevent a null pointer dereference and resource leakage in
``PyInterpreterState_New()``.

- bpo-34400: Fix undefined behavior in parsetok.c. Patch by Zackery Spytz.

- bpo-33073: Added as_integer_ratio to ints to make them more interoperable
with floats.

- bpo-34377: Update valgrind suppression list to use
``_PyObject_Free``/``_PyObject_Realloc`` instead of
``PyObject_Free``/``PyObject_Realloc``.

- bpo-34353: Added the "socket" option in the `stat.filemode()` Python
implementation to match the C implementation.

- bpo-34320: Fix ``dict(od)`` didn't copy iteration order of OrderedDict.

- bpo-34113: Fixed crash on debug builds when opcode stack was adjusted with
negative numbers. Patch by Constantin Petrisor.

- bpo-34100: Compiler now merges constants in tuples and frozensets
recursively. Code attributes like ``co_names`` are merged too.

- bpo-34151: Performance of list concatenation, repetition and slicing
operations is slightly improved. Patch by Sergey Fedoseev.

- bpo-34170: -X dev: it is now possible to override the memory allocator
using PYTHONMALLOC even if the developer mode is enabled.

- bpo-33237: Improved :exc:`AttributeError` message for partially
initialized module.

- bpo-34149: Fix min and max functions to get default behavior when key is
None.

- bpo-34125: Profiling of unbound built-in methods now works when
``**kwargs`` is given.

- bpo-34141: Optimized pickling atomic types (None, bool, int, float, bytes,
str).

- bpo-34126: Fix crashes when profiling certain invalid calls of unbound
methods. Patch by Jeroen Demeyer.

- bpo-24618: Fixed reading invalid memory when create the code object with
too small varnames tuple or too large argument counts.

- bpo-34068: In :meth:`io.IOBase.close`, ensure that the
:attr:`~io.IOBase.closed` attribute is not set with a live exception.
Patch by Zackery Spytz and Serhiy Storchaka.

- bpo-34087: Fix buffer overflow while converting unicode to numeric values.

- bpo-34080: Fixed a memory leak in the compiler when it raised some
uncommon errors during tokenizing.

- bpo-34066: Disabled interruption by Ctrl-C between calling ``open()`` and
entering a **with** block in ``with open()``.

- bpo-34042: Fix dict.copy() to maintain correct total refcount (as reported
by sys.gettotalrefcount()).

- bpo-33418: Fix potential memory leak in function object when it creates
reference cycle.

- bpo-33985: Implement contextvars.ContextVar.name attribute.

- bpo-33956: Update vendored Expat library copy to version 2.2.5.

- bpo-24596: Decref the module object in :c:func:`PyRun_SimpleFileExFlags`
before calling :c:func:`PyErr_Print()`. Patch by Zackery Spytz.

- bpo-33451: Close directly executed pyc files before calling
``PyEval_EvalCode()``.

- bpo-1617161: The hash of :class:`BuiltinMethodType` instances (methods of
built-in classes) now depends on the hash of the identity of *__self__*
instead of its value. The hash and equality of :class:`ModuleType` and
:class:`MethodWrapperType` instances (methods of user-defined classes and
some methods of built-in classes like ``str.__add__``) now depend on the
hash and equality of the identity of *__self__* instead of its value.
:class:`MethodWrapperType` instances no longer support ordering.

- bpo-33824: Fix "LC_ALL=C python3.7 -V": reset properly the command line
parser when the encoding changes after reading the Python configuration.

- bpo-33803: Fix a crash in hamt.c caused by enabling GC tracking for an
object that hadn't all of its fields set to NULL.

- bpo-33738: Seven macro incompatibilities with the Limited API were fixed,
and the macros :c:func:`PyIter_Check`, :c:func:`PyIndex_Check` and
:c:func:`PyExceptionClass_Name` were added as functions. A script for
automatic macro checks was added.

- bpo-33786: Fix asynchronous generators to handle GeneratorExit in athrow()
correctly

- bpo-30167: ``PyRun_SimpleFileExFlags`` removes ``__cached__`` from module
in addition to ``__file__``.

- bpo-33706: Fix a crash in Python initialization when parsing the command
line options. Thanks Christoph Gohlke for the bug report and the fix!

- bpo-33597: Reduce ``PyGC_Head`` size from 3 words to 2 words.

- bpo-30654: Fixed reset of the SIGINT handler to SIG_DFL on interpreter
shutdown even when there was a custom handler set previously. Patch by
Philipp Kerling.

- bpo-33622: Fixed a leak when the garbage collector fails to add an object
with the ``__del__`` method or referenced by it into the
:data:`gc.garbage` list. :c:func:`PyGC_Collect` can now be called when an
exception is set and preserves it.

- bpo-33462: Make dict and dict views reversible. Patch by Rémi Lapeyre.

- bpo-23722: A :exc:`RuntimeError` is now raised when the custom metaclass
doesn't provide the ``__classcell__`` entry in the namespace passed to
``type.__new__``. A :exc:`DeprecationWarning` was emitted in Python
3.6--3.7.

- bpo-33499: Add :envvar:`PYTHONPYCACHEPREFIX` environment variable and
:option:`-X` ``pycache_prefix`` command-line option to set an alternate
root directory for writing module bytecode cache files.

- bpo-25711: The :mod:`zipimport` module has been rewritten in pure Python.

- bpo-33509: Fix module_globals parameter of warnings.warn_explicit(): don't
crash if module_globals is not a dict.

- bpo-31849: Fix signed/unsigned comparison warning in pyhash.c.

- bpo-33475: Fixed miscellaneous bugs in converting annotations to strings
and optimized parentheses in the string representation.

- bpo-20104: Added support for the `setpgroup`, `resetids`, `setsigmask`,
`setsigdef` and `scheduler` parameters of `posix_spawn`. Patch by Pablo
Galindo.

- bpo-33391: Fix a leak in set_symmetric_difference().

- bpo-33363: Raise a SyntaxError for ``async with`` and ``async for``
statements outside of async functions.

- bpo-28055: Fix unaligned accesses in siphash24(). Patch by Rolf Eike Beer.

- bpo-33128: Fix a bug that causes PathFinder to appear twice on
sys.meta_path. Patch by Pablo Galindo Salgado.

- bpo-33331: Modules imported last are now cleared first at interpreter
shutdown.

- bpo-33312: Fixed clang ubsan (undefined behavior sanitizer) warnings in
dictobject.c by adjusting how the internal struct _dictkeysobject shared
keys structure is declared.

- bpo-33305: Improved syntax error messages for invalid numerical literals.

- bpo-33306: Improved syntax error messages for unbalanced parentheses.

- bpo-33234: The list constructor will pre-size and not over-allocate when
the input length is known.

- bpo-33270: Intern the names for all anonymous code objects. Patch by
Zackery Spytz.

- bpo-30455: The C and Python code and the documentation related to tokens
are now generated from a single source file :file:`Grammar/Tokens`.

- bpo-33176: Add a ``toreadonly()`` method to memoryviews.

- bpo-33231: Fix potential memory leak in ``normalizestring()``.

- bpo-33205: Change dict growth function from
``round_up_to_power_2(used*2+hashtable_size/2)`` to
``round_up_to_power_2(used*3)``. Previously, dict is shrinked only when
``used == 0``. Now dict has more chance to be shrinked.

- bpo-29922: Improved error messages in 'async with' when ``__aenter__()``
or ``__aexit__()`` return non-awaitable object.

- bpo-33199: Fix ``ma_version_tag`` in dict implementation is uninitialized
when copying from key-sharing dict.

- bpo-33053: When using the -m switch, sys.path[0] is now explicitly
expanded as the *starting* working directory, rather than being left as
the empty path (which allows imports from the current working directory at
the time of the import)

- bpo-33138: Changed standard error message for non-pickleable and
non-copyable types. It now says "cannot pickle" instead of "can't pickle"
or "cannot serialize".

- bpo-33018: Improve consistency of errors raised by ``issubclass()`` when
called with a non-class and an abstract base class as the first and second
arguments, respectively. Patch by Josh Bronson.

- bpo-33083: ``math.factorial`` no longer accepts arguments that are not
int-like. Patch by Pablo Galindo.

- bpo-33041: Added new opcode :opcode:`END_ASYNC_FOR` and fixes the
following issues:

* Setting global :exc:`StopAsyncIteration` no longer breaks ``async for``
loops.
* Jumping into an ``async for`` loop is now disabled.
* Jumping out of an ``async for`` loop no longer corrupts the stack.

- bpo-25750: Fix rare Python crash due to bad refcounting in
``type_getattro()`` if a descriptor deletes itself from the class. Patch
by Jeroen Demeyer.

- bpo-33041: Fixed bytecode generation for "async for" with a complex
target. A StopAsyncIteration raised on assigning or unpacking will be now
propagated instead of stopping the iteration.

- bpo-33026: Fixed jumping out of "with" block by setting f_lineno.

- bpo-33005: Fix a crash on fork when using a custom memory allocator (ex:
using PYTHONMALLOC env var). _PyGILState_Reinit() and
_PyInterpreterState_Enable() now use the default RAW memory allocator to
allocate a new interpreters mutex on fork.

- bpo-32911: Due to unexpected compatibility issues discovered during
downstream beta testing, reverted :issue:`29463`. ``docstring`` field is
removed from Module, ClassDef, FunctionDef, and AsyncFunctionDef ast nodes
which was added in 3.7a1. Docstring expression is restored as a first
statement in their body. Based on patch by Inada Naoki.

- bpo-17288: Prevent jumps from 'return' and 'exception' trace events.

- bpo-32946: Importing names from already imported module with "from ...
import ..." is now 30% faster if the module is not a package.

- bpo-32932: Make error message more revealing when there are non-str
objects in ``__all__``.

- bpo-32925: Optimized iterating and containing test for literal lists
consisting of non-constants: ``x in [a, b]`` and ``for x in [a, b]``. The
case of all constant elements already was optimized.

- bpo-32889: Update Valgrind suppression list to account for the rename of
``Py_ADDRESS_IN_RANG`` to ``address_in_range``.

- bpo-32836: Don't use temporary variables in cases of list/dict/set
comprehensions

- bpo-31356: Remove the new API added in bpo-31356 (gc.ensure_disabled()
context manager).

- bpo-32305: For namespace packages, ensure that both ``__file__`` and
``__spec__.origin`` are set to None.

- bpo-32303: Make sure ``__spec__.loader`` matches ``__loader__`` for
namespace packages.

- bpo-32711: Fix the warning messages for Python/ast_unparse.c. Patch by
Stéphane Wirtel

- bpo-32583: Fix possible crashing in builtin Unicode decoders caused by
write out-of-bound errors when using customized decode error handlers.

- bpo-32489: A :keyword:`continue` statement is now allowed in the
:keyword:`finally` clause.

- bpo-17611: Simplified the interpreter loop by moving the logic of
unrolling the stack of blocks into the compiler. The compiler emits now
explicit instructions for adjusting the stack of values and calling the
cleaning up code for :keyword:`break`, :keyword:`continue` and
:keyword:`return`.

Removed opcodes :opcode:`BREAK_LOOP`, :opcode:`CONTINUE_LOOP`,
:opcode:`SETUP_LOOP` and :opcode:`SETUP_EXCEPT`. Added new opcodes
:opcode:`ROT_FOUR`, :opcode:`BEGIN_FINALLY` and :opcode:`CALL_FINALLY` and
:opcode:`POP_FINALLY`. Changed the behavior of :opcode:`END_FINALLY` and
:opcode:`WITH_CLEANUP_START`.

- bpo-32285: New function unicodedata.is_normalized, which can check whether
a string is in a specific normal form.

- bpo-10544: Yield expressions are now disallowed in comprehensions and
generator expressions except the expression for the outermost iterable.

- bpo-32117: Iterable unpacking is now allowed without parentheses in yield
and return statements, e.g. ``yield 1, 2, 3, *rest``. Thanks to David
Cuthbert for the change and Jordan Chapman for added tests.

- bpo-31902: Fix the ``col_offset`` attribute for ast nodes
``ast.AsyncFor``, ``ast.AsyncFunctionDef``, and ``ast.AsyncWith``.
Previously, ``col_offset`` pointed to the keyword after ``async``.

- bpo-25862: Fix assertion failures in the ``tell()`` method of
``io.TextIOWrapper``. Patch by Zackery Spytz.

- bpo-21983: Fix a crash in `ctypes.cast()` in case the type argument is a
ctypes structured data type. Patch by Eryk Sun and Oren Milman.

- bpo-31577: Fix a crash in `os.utime()` in case of a bad ns argument. Patch
by Oren Milman.

- bpo-29832: Remove references to 'getsockaddrarg' from various socket error
messages. Patch by Oren Milman.

Library
-------

- bpo-35845: Add 'order' parameter to memoryview.tobytes().

- bpo-35864: The _asdict() method for collections.namedtuple now returns a
regular dict instead of an OrderedDict.

- bpo-35537: An ExitStack is now used internally within subprocess.Popen to
clean up pipe file handles. No behavior change in normal operation. But if
closing one handle were ever to cause an exception, the others will now be
closed instead of leaked. (patch by Giampaolo Rodola)

- bpo-35847: RISC-V needed the CTYPES_PASS_BY_REF_HACK. Fixes ctypes
Structure test_pass_by_value.

- bpo-35813: Shared memory submodule added to multiprocessing to avoid need
for serialization between processes

- bpo-35780: Fix lru_cache() errors arising in recursive, reentrant, or
multi-threaded code. These errors could result in orphan links and in the
cache being trapped in a state with fewer than the specified maximum
number of links. Fix handling of negative maxsize which should have been
treated as zero. Fix errors in toggling the "full" status flag. Fix
misordering of links when errors are encountered. Sync-up the C code and
pure Python code for the space saving path in functions with a single
positional argument. In this common case, the space overhead of an lru
cache entry is reduced by almost half. Fix counting of cache misses. In
error cases, the miss count was out of sync with the actual number of
times the underlying user function was called.

- bpo-35537: :func:`os.posix_spawn` and :func:`os.posix_spawnp` now have a
*setsid* parameter.

- bpo-23846: :class:`asyncio.ProactorEventLoop` now catches and logs send
errors when the self-pipe is full.

- bpo-34323: :mod:`asyncio`: Enhance ``IocpProactor.close()`` log: wait 1
second before the first log, then log every second. Log also the number of
seconds since ``close()`` was called.

- bpo-35674: Add a new :func:`os.posix_spawnp` function. Patch by Joannah
Nanjekye.

- bpo-35733: ``ast.Constant(boolean)`` no longer an instance of
:class:`ast.Num`. Patch by Anthony Sottile.

- bpo-35726: QueueHandler.prepare() now makes a copy of the record before
modifying and enqueueing it, to avoid affecting other handlers in the
chain.

- bpo-35719: Sped up multi-argument :mod:`math` functions atan2(),
copysign(), remainder() and hypot() by 1.3--2.5 times.

- bpo-35717: Fix KeyError exception raised when using enums and compile.
Patch contributed by Rémi Lapeyre.

- bpo-35699: Fixed detection of Visual Studio Build Tools 2017 in distutils

- bpo-32710: Fix memory leaks in asyncio ProactorEventLoop on overlapped
operation failure.

- bpo-35702: The :data:`time.CLOCK_UPTIME_RAW` constant is now available for
macOS 10.12.

- bpo-32710: Fix a memory leak in asyncio in the ProactorEventLoop when
``ReadFile()`` or ``WSASend()`` overlapped operation fail immediately:
release the internal buffer.

- bpo-35682: Fix ``asyncio.ProactorEventLoop.sendfile()``: don't attempt to
set the result of an internal future if it's already done.

- bpo-35283: Add a deprecated warning for the
:meth:`threading.Thread.isAlive` method. Patch by Dong-hee Na.

- bpo-35664: Improve operator.itemgetter() performance by 33% with optimized
argument handling and with adding a fast path for the common case of a
single non-negative integer index into a tuple (which is the typical use
case in the standard library).

- bpo-35643: Fixed a SyntaxWarning: invalid escape sequence in
Modules/_sha3/cleanup.py. Patch by Mickaël Schoentgen.

- bpo-35619: Improved support of custom data descriptors in :func:`help` and
:mod:`pydoc`.

- bpo-28503: The `crypt` module now internally uses the `crypt_r()` library
function instead of `crypt()` when available.

- bpo-35614: Fixed help() on metaclasses. Patch by Sanyam Khurana.

- bpo-35568: Expose ``raise(signum)`` as `raise_signal`

- bpo-35588: The floor division and modulo operations and the :func:`divmod`
function on :class:`fractions.Fraction` types are 2--4x faster. Patch by
Stefan Behnel.

- bpo-35585: Speed-up building enums by value, e.g. http.HTTPStatus(200).

- bpo-30561: random.gammavariate(1.0, beta) now computes the same result as
random.expovariate(1.0 / beta). This synchronizes the two algorithms and
eliminates some idiosyncrasies in the old implementation. It does however
produce a difference stream of random variables than it used to.

- bpo-35537: The :mod:`subprocess` module can now use the
:func:`os.posix_spawn` function in some cases for better performance.

- bpo-35526: Delaying the 'joke' of barry_as_FLUFL.mandatory to Python
version 4.0

- bpo-35523: Remove :mod:`ctypes` callback workaround: no longer create a
callback at startup. Avoid SELinux alert on ``import ctypes`` and ``import
uuid``.

- bpo-31784: :func:`uuid.uuid1` now calls :func:`time.time_ns` rather than
``int(time.time() * 1e9)``.

- bpo-35513: :class:`~unittest.runner.TextTestRunner` of
:mod:`unittest.runner` now uses :func:`time.perf_counter` rather than
:func:`time.time` to measure the execution time of a test:
:func:`time.time` can go backwards, whereas :func:`time.perf_counter` is
monotonic.

- bpo-35502: Fixed reference leaks in
:class:`xml.etree.ElementTree.TreeBuilder` in case of unfinished building
of the tree (in particular when an error was raised during parsing XML).

- bpo-35348: Make :func:`platform.architecture` parsing of ``file`` command
output more reliable: add the ``-b`` option to the ``file`` command to
omit the filename, force the usage of the C locale, and search also the
"shared object" pattern.

- bpo-35491: :mod:`multiprocessing`: Add ``Pool.__repr__()`` and enhance
``BaseProcess.__repr__()`` (add pid and parent pid) to ease debugging.
Pool state constant values are now strings instead of integers, for
example ``RUN`` value becomes ``'RUN'`` instead of ``0``.

- bpo-35477: :meth:`multiprocessing.Pool.__enter__` now fails if the pool is
not running: ``with pool:`` fails if used more than once.

- bpo-31446: Copy command line that was passed to CreateProcessW since this
function can change the content of the input buffer.

- bpo-35471: Python 2.4 dropped MacOS 9 support. The macpath module was
deprecated in Python 3.7. The module is now removed.

- bpo-23057: Unblock Proactor event loop when keyboard interrupt is received
on Windows

- bpo-35052: Fix xml.dom.minidom cloneNode() on a document with an entity:
pass the correct arguments to the user data handler of an entity.

- bpo-20239: Allow repeated assignment deletion of
:class:`unittest.mock.Mock` attributes. Patch by Pablo Galindo.

- bpo-17185: Set ``__signature__`` on mock for :mod:`inspect` to get
signature. Patch by Karthikeyan Singaravelan.

- bpo-35445: Memory errors during creating posix.environ no longer ignored.

- bpo-35415: Validate fileno= argument to socket.socket().

- bpo-35424: :class:`multiprocessing.Pool` destructor now emits
:exc:`ResourceWarning` if the pool is still running.

- bpo-35330: When a :class:`Mock` instance was used to wrap an object, if
`side_effect` is used in one of the mocks of it methods, don't call the
original implementation and return the result of using the side effect the
same way that it is done with return_value.

- bpo-35346: Drop Mac OS 9 and Rhapsody support from the :mod:`platform`
module. Rhapsody last release was in 2000. Mac OS 9 last release was in
2001.

- bpo-10496: :func:`~distutils.utils.check_environ` of
:mod:`distutils.utils` now catches :exc:`KeyError` on calling
:func:`pwd.getpwuid`: don't create the ``HOME`` environment variable in
this case.

- bpo-10496: :func:`posixpath.expanduser` now returns the input *path*
unchanged if the ``HOME`` environment variable is not set and the current
user has no home directory (if the current user identifier doesn't exist
in the password database). This change fix the :mod:`site` module if the
current user doesn't exist in the password database (if the user has no
home directory).

- bpo-35389: :func:`platform.libc_ver` now uses
``os.confstr('CS_GNU_LIBC_VERSION')`` if available and the *executable*
parameter is not set.

- bpo-35394: Add empty slots to asyncio abstract protocols.

- bpo-35310: Fix a bug in :func:`select.select` where, in some cases, the
file descriptor sequences were returned unmodified after a signal
interruption, even though the file descriptors might not be ready yet.
:func:`select.select` will now always return empty lists if a timeout has
occurred. Patch by Oran Avraham.

- bpo-35380: Enable TCP_NODELAY on Windows for proactor asyncio event loop.

- bpo-35341: Add generic version of ``collections.OrderedDict`` to the
``typing`` module. Patch by Ismo Toijala.

- bpo-35371: Fixed possible crash in ``os.utime()`` on Windows when pass
incorrect arguments.

- bpo-35346: :func:`platform.uname` now redirects ``stderr`` to
:data:`os.devnull` when running external programs like ``cmd /c ver``.

- bpo-35066: Previously, calling the strftime() method on a datetime object
with a trailing '%' in the format string would result in an exception.
However, this only occurred when the datetime C module was being used; the
python implementation did not match this behavior. Datetime is now PEP-399
compliant, and will not throw an exception on a trailing '%'.

- bpo-35345: The function `platform.popen` has been removed, it was
deprecated since Python 3.3: use :func:`os.popen` instead.

- bpo-35344: On macOS, :func:`platform.platform` now uses
:func:`platform.mac_ver`, if it returns a non-empty release string, to get
the macOS version rather than the darwin version.

- bpo-35312: Make ``lib2to3.pgen2.parse.ParseError`` round-trip pickle-able.
Patch by Anthony Sottile.

- bpo-35308: Fix regression in ``webbrowser`` where default browsers may be
preferred over browsers in the ``BROWSER`` environment variable.

- bpo-24746: Avoid stripping trailing whitespace in doctest fancy diff.
Original patch by R. David Murray & Jairo Trad. Enhanced by Sanyam
Khurana.

- bpo-28604: :func:`locale.localeconv` now sets temporarily the ``LC_CTYPE``
locale to the ``LC_MONETARY`` locale if the two locales are different and
monetary strings are non-ASCII. This temporary change affects other
threads.

- bpo-35277: Update ensurepip to install pip 18.1 and setuptools 40.6.2.

- bpo-24209: Adds IPv6 support when invoking http.server directly.

- bpo-35226: Recursively check arguments when testing for equality of
:class:`unittest.mock.call` objects and add note that tracking of
parameters used to create ancestors of mocks in ``mock_calls`` is not
possible.

- bpo-29564: The warnings module now suggests to enable tracemalloc if the
source is specified, the tracemalloc module is available, but tracemalloc
is not tracing memory allocations.

- bpo-35189: Modify the following fnctl function to retry if interrupted by
a signal (EINTR): flock, lockf, fnctl

- bpo-30064: Use add_done_callback() in sock_* asyncio API to unsubscribe
reader/writer early on calcellation.

- bpo-35186: Removed the "built with" comment added when ``setup.py upload``
is used with either ``bdist_rpm`` or ``bdist_dumb``.

- bpo-35152: Allow sending more than 2 GB at once on a multiprocessing
connection on non-Windows systems.

- bpo-35062: Fix incorrect parsing of
:class:`_io.IncrementalNewlineDecoder`'s *translate* argument.

- bpo-35065: Remove `StreamReaderProtocol._untrack_reader`. The call to
`_untrack_reader` is currently performed too soon, causing the protocol to
forget about the reader before `connection_lost` can run and feed the EOF
to the reader.

- bpo-34160: ElementTree and minidom now preserve the attribute order
specified by the user.

- bpo-35079: Improve difflib.SequenceManager.get_matching_blocks doc by
adding 'non-overlapping' and changing '!=' to '<'.

- bpo-33710: Deprecated ``l*gettext()`` functions and methods in the
:mod:`gettext` module. They return encoded bytes instead of Unicode
strings and are artifacts from Python 2 times. Also deprecated functions
and methods related to setting the charset for ``l*gettext()`` functions
and methods.

- bpo-35017: :meth:`socketserver.BaseServer.serve_forever` now exits
immediately if it's :meth:`~socketserver.BaseServer.shutdown` method is
called while it is polling for new events.

- bpo-35024: `importlib` no longer logs `wrote <bytecode path>` redundantly
after `(created|could not create) <bytecode path>` is already logged.
Patch by Quentin Agren.

- bpo-35047: ``unittest.mock`` now includes mock calls in exception messages
if ``assert_not_called``, ``assert_called_once``, or
``assert_called_once_with`` fails. Patch by Petter Strandmark.

- bpo-31047: Fix ``ntpath.abspath`` regression where it didn't remove a
trailing separator on Windows. Patch by Tim Graham.

- bpo-35053: tracemalloc now tries to update the traceback when an object is
reused from a "free list" (optimization for faster object creation, used
by the builtin list type for example).

- bpo-31553: Add the --json-lines option to json.tool. Patch by hongweipeng.

- bpo-34794: Fixed a leak in Tkinter when pass the Python wrapper around
Tcl_Obj back to Tcl/Tk.

- bpo-34909: Enum: fix grandchildren subclassing when parent mixed with
concrete data types.

- bpo-35022: :class:`unittest.mock.MagicMock` now supports the
``__fspath__`` method (from :class:`os.PathLike`).

- bpo-35008: Fixed references leaks when call the ``__setstate__()`` method
of :class:`xml.etree.ElementTree.Element` in the C implementation for
already initialized element.

- bpo-23420: Verify the value for the parameter '-s' of the cProfile CLI.
Patch by Robert Kuska

- bpo-33947: dataclasses now handle recursive reprs without raising
RecursionError.

- bpo-34890: Make :func:`inspect.iscoroutinefunction`,
:func:`inspect.isgeneratorfunction` and :func:`inspect.isasyncgenfunction`
work with :func:`functools.partial`. Patch by Pablo Galindo.

- bpo-34521: Use :func:`socket.CMSG_SPACE` to calculate ancillary data size
instead of :func:`socket.CMSG_LEN` in
:func:`multiprocessing.reduction.recvfds` as :rfc:`3542` requires the use
of the former for portable applications.

- bpo-31522: The `mailbox.mbox.get_string` function *from_* parameter can
now successfully be set to a non-default value.

- bpo-34970: Protect tasks weak set manipulation in ``asyncio.all_tasks()``

- bpo-34969: gzip: Add --fast, --best on the gzip CLI, these parameters will
be used for the fast compression method (quick) or the best method
compress (slower, but smaller file). Also, change the default compression
level to 6 (tradeoff).

- bpo-16965: The :term:`2to3` :2to3fixer:`execfile` fixer now opens the file
with mode ``'rb'``. Patch by Zackery Spytz.

- bpo-34966: :mod:`pydoc` now supports aliases not only to methods defined
in the end class, but also to inherited methods. The docstring is not
duplicated for aliases.

- bpo-34926: :meth:`mimetypes.MimeTypes.guess_type` now accepts
:term:`path-like object` in addition to url strings. Patch by Mayank
Asthana.

- bpo-23831: Add ``moveto()`` method to the ``tkinter.Canvas`` widget. Patch
by Juliette Monsel.

- bpo-34941: Methods ``find()``, ``findtext()`` and ``findall()`` of the
``Element`` class in the :mod:`xml.etree.ElementTree` module are now able
to find children which are instances of ``Element`` subclasses.

- bpo-32680: :class:`smtplib.SMTP` objects now always have a `sock`
attribute present

- bpo-34769: Fix for async generators not finalizing when event loop is in
debug mode and garbage collector runs in another thread.

- bpo-34936: Fix ``TclError`` in ``tkinter.Spinbox.selection_element()``.
Patch by Juliette Monsel.

- bpo-34829: Add methods ``selection_from``, ``selection_range``,
``selection_present`` and ``selection_to`` to the ``tkinter.Spinbox`` for
consistency with the ``tkinter.Entry`` widget. Patch by Juliette Monsel.

- bpo-34911: Added *secure_protocols* argument to
*http.cookiejar.DefaultCookiePolicy* to allow for tweaking of protocols
and also to add support by default for *wss*, the secure websocket
protocol.

- bpo-34922: Fixed integer overflow in the :meth:`~hashlib.shake.digest()`
and :meth:`~hashlib.shake.hexdigest()` methods for the SHAKE algorithm in
the :mod:`hashlib` module.

- bpo-34925: 25% speedup in argument parsing for the functions in the bisect
module.

- bpo-34900: Fixed :meth:`unittest.TestCase.debug` when used to call test
methods with subtests. Patch by Bruno Oliveira.

- bpo-34844: logging.Formatter enhancement - Ensure styles and fmt matches
in logging.Formatter - Added validate method in each format style class:
StrFormatStyle, PercentStyle, StringTemplateStyle. - This method is called
in the constructor of logging.Formatter class - Also re-raise the KeyError
in the format method of each style class, so it would a bit clear that
it's an error with the invalid format fields.

- bpo-34897: Adjust test.support.missing_compiler_executable check so that a
nominal command name of "" is ignored. Patch by Michael Felt.

- bpo-34871: Fix inspect module polluted ``sys.modules`` when parsing
``__text_signature__`` of callable.

- bpo-34898: Add `mtime` argument to `gzip.compress` for reproducible
output. Patch by Guo Ci Teo.

- bpo-28441: On Cygwin and MinGW, ensure that ``sys.executable`` always
includes the full filename in the path, including the ``.exe`` suffix
(unless it is a symbolic link).

- bpo-34866: Adding ``max_num_fields`` to ``cgi.FieldStorage`` to make DOS
attacks harder by limiting the number of ``MiniFieldStorage`` objects
created by ``FieldStorage``.

- bpo-34711: http.server ensures it reports HTTPStatus.NOT_FOUND when the
local path ends with "/" and is not a directory, even if the underlying OS
(e.g. AIX) accepts such paths as a valid file reference. Patch by Michael
Felt.

- bpo-34872: Fix self-cancellation in C implementation of asyncio.Task

- bpo-34849: Don't log waiting for ``selector.select`` in asyncio loop
iteration. The waiting is pretty normal for any asyncio program, logging
its time just adds a noise to logs without any useful information
provided.

- bpo-34022: The :envvar:`SOURCE_DATE_EPOCH` environment variable no longer
overrides the value of the *invalidation_mode* argument to
:func:`py_compile.compile`, and determines its default value instead.

- bpo-34819: Use a monotonic clock to compute timeouts in
:meth:`Executor.map` and :func:`as_completed`, in order to prevent
timeouts from deviating when the system clock is adjusted.

- bpo-34758: Add .wasm -> application/wasm to list of recognized file types
and content type headers

- bpo-34789: :func:`xml.sax.make_parser` now accepts any iterable as its
*parser_list* argument. Patch by Andrés Delfino.

- bpo-34334: In :class:`QueueHandler`, clear `exc_text` from
:class:`LogRecord` to prevent traceback from being written twice.

- bpo-34687: On Windows, asyncio now uses ProactorEventLoop, instead of
SelectorEventLoop, by default.

- bpo-5950: Support reading zip files with archive comments in
:mod:`zipimport`.

- bpo-32892: The parser now represents all constants as
:class:`ast.Constant` instead of using specific constant AST types
(``Num``, ``Str``, ``Bytes``, ``NameConstant`` and ``Ellipsis``). These
classes are considered deprecated and will be removed in future Python
versions.

- bpo-34728: Add deprecation warning when `loop` is used in methods:
`asyncio.sleep`, `asyncio.wait` and `asyncio.wait_for`.

- bpo-34738: ZIP files created by :mod:`distutils` will now include entries
for directories.

- bpo-34659: Add an optional *initial* argument to itertools.accumulate().

- bpo-29577: Support multiple mixin classes when creating Enums.

- bpo-34670: Add SSLContext.post_handshake_auth and
SSLSocket.verify_client_post_handshake for TLS 1.3's post handshake
authentication feature.

- bpo-32718: The Activate.ps1 script from venv works with PowerShell Core
6.1 and is now available under all operating systems.

- bpo-31177: Fix bug that prevented using :meth:`reset_mock
<unittest.mock.Mock.reset_mock>` on mock instances with deleted attributes

- bpo-34672: Add a workaround, so the ``'Z'`` :func:`time.strftime`
specifier on the musl C library can work in some cases.

- bpo-34666: Implement ``asyncio.StreamWriter.awrite`` and
``asyncio.StreamWriter.aclose()`` coroutines. Methods are needed for
providing a consistent stream API with control flow switched on by
default.

- bpo-6721: Acquire the logging module's commonly used internal locks while
fork()ing to avoid deadlocks in the child process.

- bpo-34658: Fix a rare interpreter unhandled exception state SystemError
only seen when using subprocess with a preexec_fn while an after_parent
handler has been registered with os.register_at_fork and the fork system
call fails.

- bpo-34652: Ensure :func:`os.lchmod` is never defined on Linux.

- bpo-34638: Store a weak reference to stream reader to break strong
references loop between reader and protocol. It allows to detect and
close the socket if the stream is deleted (garbage collected) without
``close()`` call.

- bpo-34536: `Enum._missing_`: raise `ValueError` if None returned and
`TypeError` if non-member is returned.

- bpo-34636: Speed up re scanning of many non-matching characters for \s \w
and \d within bytes objects. (microoptimization)

- bpo-24412: Add :func:`~unittest.addModuleCleanup()` and
:meth:`~unittest.TestCase.addClassCleanup()` to unittest to support
cleanups for :func:`~unittest.setUpModule()` and
:meth:`~unittest.TestCase.setUpClass()`. Patch by Lisa Roach.

- bpo-34630: Don't log SSL certificate errors in asyncio code (connection
error logging is skipped already).

- bpo-32490: Prevent filename duplication in :mod:`subprocess` exception
messages. Patch by Zackery Spytz.

- bpo-34363: dataclasses.asdict() and .astuple() now handle namedtuples
correctly.

- bpo-34625: Update vendorized expat library version to 2.2.6.

- bpo-32270: The subprocess module no longer mistakenly closes redirected
fds even when they were in pass_fds when outside of the default {0, 1, 2}
set.

- bpo-34622: Create a dedicated ``asyncio.CancelledError``,
``asyncio.InvalidStateError`` and ``asyncio.TimeoutError`` exception
classes. Inherit them from corresponding exceptions from
``concurrent.futures`` package. Extract ``asyncio`` exceptions into a
separate file.

- bpo-34610: Fixed iterator of :class:`multiprocessing.managers.DictProxy`.

- bpo-34421: Fix distutils logging for non-ASCII strings. This caused
installation issues on Windows.

- bpo-34604: Fix possible mojibake in the error message of `pwd.getpwnam`
and `grp.getgrnam` using string representation because of invisible
characters or trailing whitespaces. Patch by William Grzybowski.

- bpo-30977: Make uuid.UUID use ``__slots__`` to reduce its memory
footprint. Based on original patch by Wouter Bolsterlee.

- bpo-34574: OrderedDict iterators are not exhausted during pickling
anymore. Patch by Sergey Fedoseev.

- bpo-8110: Refactored :mod:`subprocess` to check for Windows-specific
modules rather than ``sys.platform == 'win32'``.

- bpo-34530: ``distutils.spawn.find_executable()`` now falls back on
:data:`os.defpath` if the ``PATH`` environment variable is not set.

- bpo-34563: On Windows, fix multiprocessing.Connection for very large read:
fix _winapi.PeekNamedPipe() and _winapi.ReadFile() for read larger than
INT_MAX (usually ``2**31-1``).

- bpo-34558: Correct typo in Lib/ctypes/_aix.py

- bpo-34282: Move ``Enum._convert`` to ``EnumMeta._convert_`` and fix enum
members getting shadowed by parent attributes.

- bpo-22872: When the queue is closed, :exc:`ValueError` is now raised by
:meth:`multiprocessing.Queue.put` and :meth:`multiprocessing.Queue.get`
instead of :exc:`AssertionError` and :exc:`OSError`, respectively. Patch
by Zackery Spytz.

- bpo-34515: Fix parsing non-ASCII identifiers in
:mod:`lib2to3.pgen2.tokenize` (PEP 3131).

- bpo-13312: Avoids a possible integer underflow (undefined behavior) in the
time module's year handling code when passed a very low negative year
value.

- bpo-34472: Improved compatibility for streamed files in :mod:`zipfile`.
Previously an optional signature was not being written and certain ZIP
applications were not supported. Patch by Silas Sewell.

- bpo-34454: Fix the .fromisoformat() methods of datetime types crashing
when given unicode with non-UTF-8-encodable code points. Specifically,
datetime.fromisoformat() now accepts surrogate unicode code points used as
the separator. Report and tests by Alexey Izbyshev, patch by Paul Ganssle.

- bpo-6700: Fix inspect.getsourcelines for module level frames/tracebacks.
Patch by Vladimir Matveev.

- bpo-34171: Running the :mod:`trace` module no longer creates the
``trace.cover`` file.

- bpo-34441: Fix crash when an ``ABC``-derived class with invalid
``__subclasses__`` is passed as the second argument to
:func:`issubclass()`. Patch by Alexey Izbyshev.

- bpo-34427: Fix infinite loop in ``a.extend(a)`` for ``MutableSequence``
subclasses.

- bpo-34412: Make :func:`signal.strsignal` work on HP-UX. Patch by Michael
Osipov.

- bpo-20849: shutil.copytree now accepts a new ``dirs_exist_ok`` keyword
argument. Patch by Josh Bronson.

- bpo-31715: Associate ``.mjs`` file extension with
``application/javascript`` MIME Type.

- bpo-34384: :func:`os.readlink` now accepts :term:`path-like <path-like
object>` and :class:`bytes` objects on Windows.

- bpo-22602: The UTF-7 decoder now raises :exc:`UnicodeDecodeError` for
ill-formed sequences starting with "+" (as specified in RFC 2152). Patch
by Zackery Spytz.

- bpo-2122: The :meth:`mmap.flush() <mmap.mmap.flush>` method now returns
``None`` on success, raises an exception on error under all platforms.

- bpo-34341: Appending to the ZIP archive with the ZIP64 extension no longer
grows the size of extra fields of existing entries.

- bpo-34333: Fix %-formatting in :meth:`pathlib.PurePath.with_suffix` when
formatting an error message.

- bpo-18540: The :class:`imaplib.IMAP4` and :class:`imaplib.IMAP4_SSL`
classes now resolve to the local host IP correctly when the default value
of *host* parameter (``''``) is used.

- bpo-26502: Implement ``traceback.FrameSummary.__len__()`` method to
preserve compatibility with the old tuple API.

- bpo-34318: :func:`~unittest.TestCase.assertRaises`,
:func:`~unittest.TestCase.assertRaisesRegex`,
:func:`~unittest.TestCase.assertWarns` and
:func:`~unittest.TestCase.assertWarnsRegex` no longer success if the
passed callable is None. They no longer ignore unknown keyword arguments
in the context manager mode. A DeprecationWarning was raised in these
cases since Python 3.5.

- bpo-9372: Deprecate :meth:`__getitem__` methods of
:class:`xml.dom.pulldom.DOMEventStream`, :class:`wsgiref.util.FileWrapper`
and :class:`fileinput.FileInput`.

- bpo-33613: Fix a race condition in ``multiprocessing.semaphore_tracker``
when the tracker receives SIGINT before it can register signal handlers
for ignoring it.

- bpo-34248: Report filename in the exception raised when the database file
cannot be opened by :func:`dbm.gnu.open` and :func:`dbm.ndbm.open` due to
OS-related error. Patch by Zsolt Cserna.

- bpo-33089: Add math.dist() to compute the Euclidean distance between two
points.

- bpo-34246: :meth:`smtplib.SMTP.send_message` no longer modifies the
content of the *mail_options* argument. Patch by Pablo S. Blum de Aguiar.

- bpo-31047: Fix ``ntpath.abspath`` for invalid paths on windows. Patch by
Franz Woellert.

- bpo-32321: Add pure Python fallback for functools.reduce. Patch by Robert
Wright.

- bpo-34270: The default asyncio task class now always has a name which can
be get or set using two new methods (:meth:`~asyncio.Task.get_name()` and
:meth:`~asyncio.Task.set_name`) and is visible in the :func:`repr` output.
An initial name can also be set using the new ``name`` keyword argument to
:func:`asyncio.create_task` or the
:meth:`~asyncio.AbstractEventLoop.create_task` method of the event loop.
If no initial name is set, the default Task implementation generates a
name like ``Task-1`` using a monotonic counter.

- bpo-34263: asyncio's event loop will not pass timeouts longer than one day
to epoll/select etc.

- bpo-34035: Fix several AttributeError in zipfile seek() methods. Patch by
Mickaël Schoentgen.

- bpo-32215: Fix performance regression in :mod:`sqlite3` when a DML
statement appeared in a different line than the rest of the SQL query.

- bpo-34075: Deprecate passing non-ThreadPoolExecutor instances to
:meth:`AbstractEventLoop.set_default_executor`.

- bpo-34251: Restore ``msilib.Win64`` to preserve backwards compatibility
since it's already used by :mod:`distutils`' ``bdist_msi`` command.

- bpo-19891: Ignore errors caused by missing / non-writable homedir while
writing history during exit of an interactive session. Patch by Anthony
Sottile.

- bpo-33089: Enhanced math.hypot() to support more than two dimensions.

- bpo-34228: tracemalloc: PYTHONTRACEMALLOC=0 environment variable and -X
tracemalloc=0 command line option are now allowed to disable explicitly
tracemalloc at startup.

- bpo-13041: Use :func:`shutil.get_terminal_size` to calculate the terminal
width correctly in the ``argparse.HelpFormatter`` class. Initial patch by
Zbyszek Jędrzejewski-Szmek.

- bpo-34213: Allow frozen dataclasses to have a field named "object".
Previously this conflicted with an internal use of "object".

- bpo-34052: :meth:`sqlite3.Connection.create_aggregate`,
:meth:`sqlite3.Connection.create_function`,
:meth:`sqlite3.Connection.set_authorizer`,
:meth:`sqlite3.Connection.set_progress_handler` methods raises TypeError
when unhashable objects are passed as callable. These methods now don't
pass such objects to SQLite API. Previous behavior could lead to
segfaults. Patch by Sergey Fedoseev.

- bpo-34197: Attributes *skipinitialspace*, *doublequote* and *strict* of
the *dialect* attribute of the :mod:`csv` reader are now :class:`bool`
instances instead of integers 0 or 1.

- bpo-32788: Errors other than :exc:`TypeError` raised in methods
``__adapt__()`` and ``__conform__()`` in the :mod:`sqlite3` module are now
propagated to the user.

- bpo-21446: The :2to3fixer:`reload` fixer now uses :func:`importlib.reload`
instead of deprecated :func:`imp.reload`.

- bpo-940286: pydoc's ``Helper.showtopic()`` method now prints the cross
references of a topic correctly.

- bpo-34164: :func:`base64.b32decode` could raise UnboundLocalError or
OverflowError for incorrect padding. Now it always raises
:exc:`base64.Error` in these cases.

- bpo-33729: Fixed issues with arguments parsing in :mod:`hashlib`.

- bpo-34097: ZipFile can zip files older than 1980-01-01 and newer than
2107-12-31 using a new ``strict_timestamps`` parameter at the cost of
setting the timestamp to the limit.

- bpo-34108: Remove extraneous CR in 2to3 refactor.

- bpo-34070: Make sure to only check if the handle is a tty, when opening a
file with ``buffering=-1``.

- bpo-27494: Reverted :issue:`27494`. 2to3 rejects now a trailing comma in
generator expressions.

- bpo-33967: functools.singledispatch now raises TypeError instead of
IndexError when no positional arguments are passed.

- bpo-34041: Add the parameter *deterministic* to the
:meth:`sqlite3.Connection.create_function` method. Patch by Sergey
Fedoseev.

- bpo-34056: Ensure the loader shim created by ``imp.load_module`` always
returns bytes from its ``get_data()`` function. This fixes using
``imp.load_module`` with :pep:`552` hash-based pycs.

- bpo-34054: The multiprocessing module now uses the monotonic clock
:func:`time.monotonic` instead of the system clock :func:`time.time` to
implement timeout.

- bpo-34043: Optimize tarfile uncompress performance about 15% when gzip is
used.

- bpo-34044: ``subprocess.Popen`` now copies the *startupinfo* argument to
leave it unchanged: it will modify the copy, so that the same
``STARTUPINFO`` object can be used multiple times.

- bpo-34010: Fixed a performance regression for reading streams with
tarfile. The buffered read should use a list, instead of appending to a
bytes object.

- bpo-34019: webbrowser: Correct the arguments passed to Opera Browser when
opening a new URL using the ``webbrowser`` module. Patch by Bumsik Kim.

- bpo-34003: csv.DictReader now creates dicts instead of OrderedDicts. Patch
by Michael Selik.

- bpo-33978: Closed existing logging handlers before reconfiguration via
fileConfig and dictConfig. Patch by Karthikeyan Singaravelan.

- bpo-14117: Make minor tweaks to turtledemo. The 'wikipedia' example is now
'rosette', describing what it draws. The 'penrose' print output is
reduced. The'1024' output of 'tree' is eliminated.

- bpo-33974: Fixed passing lists and tuples of strings containing special
characters ``"``, ``\``, ``{``, ``}`` and ``\n`` as options to
:mod:`~tkinter.ttk` widgets.

- bpo-27500: Fix getaddrinfo to resolve IPv6 addresses correctly.

- bpo-24567: Improve random.choices() to handle subnormal input weights that
could occasionally trigger an IndexError.

- bpo-33871: Fixed integer overflow in :func:`os.readv`, :func:`os.writev`,
:func:`os.preadv` and :func:`os.pwritev` and in :func:`os.sendfile` with
*headers* or *trailers* arguments (on BSD-based OSes and macOS).

- bpo-25007: Add :func:`copy.copy` and :func:`copy.deepcopy` support to zlib
compressors and decompressors. Patch by Zackery Spytz.

- bpo-33929: multiprocessing: Fix a race condition in Popen of
multiprocessing.popen_spawn_win32. The child process now duplicates the
read end of pipe instead of "stealing" it. Previously, the read end of
pipe was "stolen" by the child process, but it leaked a handle if the
child process had been terminated before it could steal the handle from
the parent process.

- bpo-33899: Tokenize module now implicitly emits a NEWLINE when provided
with input that does not have a trailing new line. This behavior now
matches what the C tokenizer does internally. Contributed by Ammar Askar.

- bpo-33897: Added a 'force' keyword argument to logging.basicConfig().

- bpo-33695: :func:`shutil.copytree` uses :func:`os.scandir` function and
all copy functions depending from it use cached :func:`os.stat` values.
The speedup for copying a directory with 8000 files is around +9% on
Linux, +20% on Windows and + 30% on a Windows SMB share. Also the number
of :func:`os.stat` syscalls is reduced by 38% making
:func:`shutil.copytree` especially faster on network filesystems.
(Contributed by Giampaolo Rodola' in :issue:`33695`.)

- bpo-33916: bz2 and lzma: When Decompressor.__init__() is called twice,
free the old lock to not leak memory.

- bpo-32568: Make select.epoll() and its documentation consistent regarding
*sizehint* and *flags*.

- bpo-33833: Fixed bug in asyncio where ProactorSocketTransport logs
AssertionError if force closed during write.

- bpo-33663: Convert content length to string before putting to header.

- bpo-33721: :mod:`os.path` functions that return a boolean result like
:func:`~os.path.exists`, :func:`~os.path.lexists`, :func:`~os.path.isdir`,
:func:`~os.path.isfile`, :func:`~os.path.islink`, and
:func:`~os.path.ismount`, and :mod:`pathlib.Path` methods that return a
boolean result like :meth:`~pathlib.Path.exists()`,
:meth:`~pathlib.Path.is_dir()`, :meth:`~pathlib.Path.is_file()`,
:meth:`~pathlib.Path.is_mount()`, :meth:`~pathlib.Path.is_symlink()`,
:meth:`~pathlib.Path.is_block_device()`,
:meth:`~pathlib.Path.is_char_device()`, :meth:`~pathlib.Path.is_fifo()`,
:meth:`~pathlib.Path.is_socket()` now return ``False`` instead of raising
:exc:`ValueError` or its subclasses :exc:`UnicodeEncodeError` and
:exc:`UnicodeDecodeError` for paths that contain characters or bytes
unrepresentable at the OS level.

- bpo-26544: Fixed implementation of :func:`platform.libc_ver`. It almost
always returned version '2.9' for glibc.

- bpo-33843: Remove deprecated ``cgi.escape``, ``cgi.parse_qs`` and
``cgi.parse_qsl``.

- bpo-33842: Remove ``tarfile.filemode`` which is deprecated since Python
3.3.

- bpo-30167: Prevent site.main() exception if PYTHONSTARTUP is set. Patch by
Steve Weber.

- bpo-33805: Improve error message of dataclasses.replace() when an InitVar
is not specified

- bpo-33687: Fix the call to ``os.chmod()`` for ``uu.decode()`` if a mode is
given or decoded. Patch by Timo Furrer.

- bpo-33812: Datetime instance d with non-None tzinfo, but with
d.tzinfo.utcoffset(d) returning None is now treated as naive by the
astimezone() method.

- bpo-32108: In configparser, don't clear section when it is assigned to
itself.

- bpo-27397: Make email module properly handle invalid-length base64
strings.

- bpo-33578: Implement multibyte encoder/decoder state methods

- bpo-30805: Avoid race condition with debug logging

- bpo-33476: Fix _header_value_parser.py when address group is missing final
';'. Contributed by Enrique Perez-Terron

- bpo-33694: asyncio: Fix a race condition causing data loss on
pause_reading()/resume_reading() when using the ProactorEventLoop.

- bpo-32493: Correct test for ``uuid_enc_be`` availability in
``configure.ac``. Patch by Michael Felt.

- bpo-33792: Add asyncio.WindowsSelectorEventLoopPolicy and
asyncio.WindowsProactorEventLoopPolicy.

- bpo-33274: W3C DOM Level 1 specifies return value of
Element.removeAttributeNode() as "The Attr node that was removed."
xml.dom.minidom now complies with this requirement.

- bpo-33778: Update ``unicodedata``'s database to Unicode version 11.0.0.

- bpo-33165: Added a stacklevel parameter to logging calls to allow use of
wrapper/helper functions for logging APIs.

- bpo-33770: improve base64 exception message for encoded inputs of invalid
length

- bpo-33769: asyncio/start_tls: Fix error message; cancel callbacks in case
of an unhandled error; mark SSLTransport as closed if it is aborted.

- bpo-33767: The concatenation (``+``) and repetition (``*``) sequence
operations now raise :exc:`TypeError` instead of :exc:`SystemError` when
performed on :class:`mmap.mmap` objects. Patch by Zackery Spytz.

- bpo-33734: asyncio/ssl: Fix AttributeError, increase default handshake
timeout

- bpo-31014: Fixed creating a controller for :mod:`webbrowser` when a user
specifies a path to an entry in the BROWSER environment variable. Based
on patch by John Still.

- bpo-2504: Add gettext.pgettext() and variants.

- bpo-33197: Add description property for _ParameterKind

- bpo-32751: When cancelling the task due to a timeout,
:meth:`asyncio.wait_for` will now wait until the cancellation is complete.

- bpo-32684: Fix gather to propagate cancellation of itself even with
return_exceptions.

- bpo-33654: Support protocol type switching in SSLTransport.set_protocol().

- bpo-33674: Pause the transport as early as possible to further reduce the
risk of data_received() being called before connection_made().

- bpo-33671: :func:`shutil.copyfile`, :func:`shutil.copy`,
:func:`shutil.copy2`, :func:`shutil.copytree` and :func:`shutil.move` use
platform-specific fast-copy syscalls on Linux and macOS in order to copy
the file more efficiently. On Windows :func:`shutil.copyfile` uses a
bigger default buffer size (1 MiB instead of 16 KiB) and a
:func:`memoryview`-based variant of :func:`shutil.copyfileobj` is used.
The speedup for copying a 512MiB file is about +26% on Linux, +50% on
macOS and +40% on Windows. Also, much less CPU cycles are consumed.
(Contributed by Giampaolo Rodola' in :issue:`25427`.)

- bpo-33674: Fix a race condition in SSLProtocol.connection_made() of
asyncio.sslproto: start immediately the handshake instead of using
call_soon(). Previously, data_received() could be called before the
handshake started, causing the handshake to hang or fail.

- bpo-31647: Fixed bug where calling write_eof() on a
_SelectorSocketTransport after it's already closed raises AttributeError.

- bpo-32610: Make asyncio.all_tasks() return only pending tasks.

- bpo-32410: Avoid blocking on file IO in sendfile fallback code

- bpo-33469: Fix RuntimeError after closing loop that used run_in_executor

- bpo-33672: Fix Task.__repr__ crash with Cython's bogus coroutines

- bpo-33654: Fix transport.set_protocol() to support switching between
asyncio.Protocol and asyncio.BufferedProtocol. Fix loop.start_tls() to
work with asyncio.BufferedProtocols.

- bpo-33652: Pickles of type variables and subscripted generics are now
future-proof and compatible with older Python versions.

- bpo-32493: Fixed :func:`uuid.uuid1` on FreeBSD.

- bpo-33238: Add ``InvalidStateError`` to :mod:`concurrent.futures`.
``Future.set_result`` and ``Future.set_exception`` now raise
``InvalidStateError`` if the futures are not pending or running. Patch by
Jason Haydaman.

- bpo-33618: Finalize and document preliminary and experimental TLS 1.3
support with OpenSSL 1.1.1

- bpo-33625: Release GIL on `grp.getgrnam`, `grp.getgrgid`, `pwd.getpwnam`
and `pwd.getpwuid` if reentrant variants of these functions are available.
Patch by William Grzybowski.

- bpo-33623: Fix possible SIGSGV when asyncio.Future is created in __del__

- bpo-11874: Use a better regex when breaking usage into wrappable parts.
Avoids bogus assertion errors from custom metavar strings.

- bpo-30877: Fixed a bug in the Python implementation of the JSON decoder
that prevented the cache of parsed strings from clearing after finishing
the decoding. Based on patch by c-fos.

- bpo-33604: Remove HMAC default to md5 marked for removal in 3.8 (removal
originally planned in 3.6, bump to 3.8 in PR 7062).

- bpo-33582: Emit a deprecation warning for inspect.formatargspec

- bpo-21145: Add ``functools.cached_property`` decorator, for computed
properties cached for the life of the instance.

- bpo-33570: Change TLS 1.3 cipher suite settings for compatibility with
OpenSSL 1.1.1-pre6 and newer. OpenSSL 1.1.1 will have TLS 1.3 ciphers
enabled by default.

- bpo-28556: Do not simplify arguments to `typing.Union`. Now
`Union[Manager, Employee]` is not simplified to `Employee` at runtime.
Such simplification previously caused several bugs and limited
possibilities for introspection.

- bpo-12486: :func:`tokenize.generate_tokens` is now documented as a public
API to tokenize unicode strings. It was previously present but
undocumented.

- bpo-33540: Add a new ``block_on_close`` class attribute to
``ForkingMixIn`` and ``ThreadingMixIn`` classes of :mod:`socketserver`.

- bpo-33548: tempfile._candidate_tempdir_list should consider common TEMP
locations

- bpo-33109: argparse subparsers are once again not required by default,
reverting the change in behavior introduced by bpo-26510 in 3.7.0a2.

- bpo-33541: Remove unused private method ``_strptime.LocaleTime.__pad``
(a.k.a. ``_LocaleTime__pad``).

- bpo-33536: dataclasses.make_dataclass now checks for invalid field names
and duplicate fields. Also, added a check for invalid field
specifications.

- bpo-33542: Prevent ``uuid.get_node`` from using a DUID instead of a MAC on
Windows. Patch by Zvi Effron

- bpo-26819: Fix race condition with `ReadTransport.resume_reading` in
Windows proactor event loop.

- Fix failure in `typing.get_type_hints()` when ClassVar was provided as a
string forward reference.

- bpo-33516: :class:`unittest.mock.MagicMock` now supports the ``__round__``
magic method.

- bpo-28612: Added support for Site Maps to urllib's ``RobotFileParser`` as
:meth:`RobotFileParser.site_maps()
<urllib.robotparser.RobotFileParser.site_maps>`. Patch by Lady Red, based
on patch by Peter Wirtz.

- bpo-28167: Remove platform.linux_distribution, which was deprecated since
3.5.

- bpo-33504: Switch the default dictionary implementation for
:mod:`configparser` from :class:`collections.OrderedDict` to the standard
:class:`dict` type.

- bpo-33505: Optimize asyncio.ensure_future() by reordering if checks: 1.17x
faster.

- bpo-33497: Add errors param to cgi.parse_multipart and make an encoding in
FieldStorage use the given errors (needed for Twisted). Patch by Amber
Brown.

- bpo-29235: The :class:`cProfile.Profile` class can now be used as a
context manager. Patch by Scott Sanderson.

- bpo-33495: Change dataclasses.Fields repr to use the repr of each of its
members, instead of str. This makes it more clear what each field
actually represents. This is especially true for the 'type' member.

- bpo-26103: Correct ``inspect.isdatadescriptor`` to look for ``__set__`` or
``__delete__``. Patch by Aaron Hall.

- bpo-29209: Removed the ``doctype()`` method and the *html* parameter of
the constructor of :class:`~xml.etree.ElementTree.XMLParser`. The
``doctype()`` method defined in a subclass will no longer be called.
Deprecated methods ``getchildren()`` and ``getiterator()`` in the
:mod:`~xml.etree.ElementTree` module emit now a :exc:`DeprecationWarning`
instead of :exc:`PendingDeprecationWarning`.

- bpo-33453: Fix dataclasses to work if using literal string type
annotations or if using PEP 563 "Postponed Evaluation of Annotations".
Only specific string prefixes are detected for both ClassVar ("ClassVar"
and "typing.ClassVar") and InitVar ("InitVar" and "dataclasses.InitVar").

- bpo-28556: Minor fixes in typing module: add annotations to
``NamedTuple.__new__``, pass ``*args`` and ``**kwds`` in
``Generic.__new__``. Original PRs by Paulius Šarka and Chad Dombrova.

- bpo-33365: Print the header values besides the header keys instead just
the header keys if *debuglevel* is set to >0 in :mod:`http.client`. Patch
by Marco Strigl.

- bpo-20087: Updated alias mapping with glibc 2.27 supported locales.

- bpo-33422: Fix trailing quotation marks getting deleted when looking up
byte/string literals on pydoc. Patch by Andrés Delfino.

- bpo-28167: The function ``platform.linux_distribution`` and
``platform.dist`` now trigger a ``DeprecationWarning`` and have been
marked for removal in Python 3.8

- bpo-33281: Fix ctypes.util.find_library regression on macOS.

- bpo-33311: Text and html output generated by cgitb does not display
parentheses if the current call is done directly in the module. Patch by
Stéphane Blondon.

- bpo-27300: The file classes in *tempfile* now accept an *errors* parameter
that complements the already existing *encoding*. Patch by Stephan Hohe.

- bpo-32933: :func:`unittest.mock.mock_open` now supports iteration over the
file contents. Patch by Tony Flury.

- bpo-33217: Raise :exc:`TypeError` when looking up non-Enum objects in Enum
classes and Enum members.

- bpo-33197: Update error message when constructing invalid
inspect.Parameters Patch by Dong-hee Na.

- bpo-33383: Fixed crash in the get() method of the :mod:`dbm.ndbm` database
object when it is called with a single argument.

- bpo-33375: The warnings module now finds the Python file associated with a
warning from the code object, rather than the frame's global namespace.
This is consistent with how tracebacks and pdb find filenames, and should
work better for dynamically executed code.

- bpo-33336: ``imaplib`` now allows ``MOVE`` command in ``IMAP4.uid()`` (RFC
6851: IMAP MOVE Extension) and potentially as a name of supported method
of ``IMAP4`` object.

- bpo-32455: Added *jump* parameter to :func:`dis.stack_effect`.

- bpo-27485: Rename and deprecate undocumented functions in
:func:`urllib.parse`.

- bpo-33332: Add ``signal.valid_signals()`` to expose the POSIX sigfillset()
functionality.

- bpo-33251: `ConfigParser.items()` was fixed so that key-value pairs passed
in via `vars` are not included in the resulting output.

- bpo-33329: Fix multiprocessing regression on newer glibcs

- bpo-33334: :func:`dis.stack_effect` now supports all defined opcodes
including NOP and EXTENDED_ARG.

- bpo-991266: Fix quoting of the ``Comment`` attribute of
:class:`http.cookies.SimpleCookie`.

- bpo-33131: Upgrade bundled version of pip to 10.0.1.

- bpo-33308: Fixed a crash in the :mod:`parser` module when converting an ST
object to a tree of tuples or lists with ``line_info=False`` and
``col_info=True``.

- bpo-23403: lib2to3 now uses pickle protocol 4 for pre-computed grammars.

- bpo-33266: lib2to3 now recognizes ``rf'...'`` strings.

- bpo-11594: Ensure line-endings are respected when using lib2to3.

- bpo-33254: Have :func:`importlib.resources.contents` and
:meth:`importlib.abc.ResourceReader.contents` return an :term:`iterable`
instead of an :term:`iterator`.

- bpo-33265: ``contextlib.ExitStack`` and ``contextlib.AsyncExitStack`` now
use a method instead of a wrapper function for exit callbacks.

- bpo-33263: Fix FD leak in `_SelectorSocketTransport` Patch by Vlad
Starostin.

- bpo-33256: Fix display of ``<module>`` call in the html produced by
``cgitb.html()``. Patch by Stéphane Blondon.

- bpo-33144: ``random.Random()`` and its subclassing mechanism got optimized
to check only once at class/subclass instantiation time whether its
``getrandbits()`` method can be relied on by other methods, including
``randrange()``, for the generation of arbitrarily large random integers.
Patch by Wolfgang Maier.

- bpo-33185: Fixed regression when running pydoc with the :option:`-m`
switch. (The regression was introduced in 3.7.0b3 by the resolution of
:issue:`33053`)

This fix also changed pydoc to add ``os.getcwd()`` to :data:`sys.path`
when necessary, rather than adding ``"."``.

- bpo-29613: Added support for the ``SameSite`` cookie flag to the
``http.cookies`` module.

- bpo-33169: Delete entries of ``None`` in :data:`sys.path_importer_cache`
when :meth:`importlib.machinery.invalidate_caches` is called.

- bpo-33203: ``random.Random.choice()`` now raises ``IndexError`` for empty
sequences consistently even when called from subclasses without a
``getrandbits()`` implementation.

- bpo-33224: Update difflib.mdiff() for :pep:`479`. Convert an uncaught
StopIteration in a generator into a return-statement.

- bpo-33209: End framing at the end of C implementation of
:func:`pickle.Pickler.dump`.

- bpo-32861: The urllib.robotparser's ``__str__`` representation now
includes wildcard entries and the "Crawl-delay" and "Request-rate" fields.
Also removes extra newlines that were being appended to the end of the
string. Patch by Michael Lazar.

- bpo-23403: ``DEFAULT_PROTOCOL`` in :mod:`pickle` was bumped to 4. Protocol
4 is described in :pep:`3154` and available since Python 3.4. It offers
better performance and smaller size compared to protocol 3 introduced in
Python 3.0.

- bpo-20104: Improved error handling and fixed a reference leak in
:func:`os.posix_spawn()`.

- bpo-33106: Deleting a key from a read-only dbm database raises module
specific error instead of KeyError.

- bpo-33175: In dataclasses, Field.__set_name__ now looks up the
__set_name__ special method on the class, not the instance, of the default
value.

- bpo-32380: Create functools.singledispatchmethod to support generic single
dispatch on descriptors and methods.

- bpo-33141: Have Field objects pass through __set_name__ to their default
values, if they have their own __set_name__.

- bpo-33096: Allow ttk.Treeview.insert to insert iid that has a false
boolean value. Note iid=0 and iid=False would be same. Patch by Garvit
Khatri.

- bpo-32873: Treat type variables and special typing forms as immutable by
copy and pickle. This fixes several minor issues and inconsistencies, and
improves backwards compatibility with Python 3.6.

- bpo-33134: When computing dataclass's __hash__, use the lookup table to
contain the function which returns the __hash__ value. This is an
improvement over looking up a string, and then testing that string to see
what to do.

- bpo-33127: The ssl module now compiles with LibreSSL 2.7.1.

- bpo-32505: Raise TypeError if a member variable of a dataclass is of type
Field, but doesn't have a type annotation.

- bpo-33078: Fix the failure on OSX caused by the tests relying on
sem_getvalue

- bpo-33116: Add 'Field' to dataclasses.__all__.

- bpo-32896: Fix an error where subclassing a dataclass with a field that
uses a default_factory would generate an incorrect class.

- bpo-33100: Dataclasses: If a field has a default value that's a
MemberDescriptorType, then it's from that field being in __slots__, not an
actual default value.

- bpo-32953: If a non-dataclass inherits from a frozen dataclass, allow
attributes to be added to the derived class. Only attributes from the
frozen dataclass cannot be assigned to. Require all dataclasses in a
hierarchy to be either all frozen or all non-frozen.

- bpo-33097: Raise RuntimeError when ``executor.submit`` is called during
interpreter shutdown.

- bpo-32968: Modulo and floor division involving Fraction and float should
return float.

- bpo-33061: Add missing ``NoReturn`` to ``__all__`` in typing.py

- bpo-33078: Fix the size handling in multiprocessing.Queue when a pickling
error occurs.

- bpo-33064: lib2to3 now properly supports trailing commas after ``*args``
and ``**kwargs`` in function signatures.

- bpo-33056: FIX properly close leaking fds in
concurrent.futures.ProcessPoolExecutor.

- bpo-33021: Release the GIL during fstat() calls, avoiding hang of all
threads when calling mmap.mmap(), os.urandom(), and random.seed(). Patch
by Nir Soffer.

- bpo-31804: Avoid failing in multiprocessing.Process if the standard
streams are closed or None at exit.

- bpo-33034: Providing an explicit error message when casting the port
property to anything that is not an integer value using ``urlparse()`` and
``urlsplit()``. Patch by Matt Eaton.

- bpo-30249: Improve struct.unpack_from() exception messages for problems
with the buffer size and offset.

- bpo-33037: Skip sending/receiving data after SSL transport closing.

- bpo-27683: Fix a regression in :mod:`ipaddress` that result of
:meth:`hosts` is empty when the network is constructed by a tuple
containing an integer mask and only 1 bit left for addresses.

- bpo-22674: Add the strsignal() function in the signal module that returns
the system description of the given signal, as returned by strsignal(3).

- bpo-32999: Fix C implementation of ``ABC.__subclasscheck__(cls,
subclass)`` crashed when ``subclass`` is not a type object.

- bpo-33009: Fix inspect.signature() for single-parameter partialmethods.

- bpo-32969: Expose several missing constants in zlib and fix corresponding
documentation.

- bpo-32056: Improved exceptions raised for invalid number of channels and
sample width when read an audio file in modules :mod:`aifc`, :mod:`wave`
and :mod:`sunau`.

- bpo-32970: Improved disassembly of the MAKE_FUNCTION instruction.

- bpo-32844: Fix wrong redirection of a low descriptor (0 or 1) to stderr in
subprocess if another low descriptor is closed.

- bpo-32960: For dataclasses, disallow inheriting frozen from non-frozen
classes, and also disallow inheriting non-frozen from frozen classes. This
restriction will be relaxed at a future date.

- bpo-32713: Fixed tarfile.itn handling of out-of-bounds float values. Patch
by Joffrey Fuhrer.

- bpo-32257: The ssl module now contains OP_NO_RENEGOTIATION constant,
available with OpenSSL 1.1.0h or 1.1.1.

- bpo-32951: Direct instantiation of SSLSocket and SSLObject objects is now
prohibited. The constructors were never documented, tested, or designed as
public constructors. Users were suppose to use ssl.wrap_socket() or
SSLContext.

- bpo-32929: Remove the tri-state parameter "hash", and add the boolean
"unsafe_hash". If unsafe_hash is True, add a __hash__ function, but if a
__hash__ exists, raise TypeError. If unsafe_hash is False, add a __hash__
based on the values of eq= and frozen=. The unsafe_hash=False behavior is
the same as the old hash=None behavior. unsafe_hash=False is the default,
just as hash=None used to be.

- bpo-32947: Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround for TLSv1.3
for future compatibility with OpenSSL 1.1.1.

- bpo-32146: Document the interaction between frozen executables and the
spawn and forkserver start methods in multiprocessing.

- bpo-30622: The ssl module now detects missing NPN support in LibreSSL.

- bpo-32922: dbm.open() now encodes filename with the filesystem encoding
rather than default encoding.

- bpo-32759: Free unused arenas in multiprocessing.heap.

- bpo-32859: In ``os.dup2``, don't check every call whether the ``dup3``
syscall exists or not.

- bpo-32556: nt._getfinalpathname, nt._getvolumepathname and
nt._getdiskusage now correctly convert from bytes.

- bpo-21060: Rewrite confusing message from setup.py upload from "No dist
file created in earlier command" to the more helpful "Must create and
upload files in one command".

- bpo-32857: In :mod:`tkinter`, ``after_cancel(None)`` now raises a
:exc:`ValueError` instead of canceling the first scheduled function.
Patch by Cheryl Sabella.

- bpo-32852: Make sure sys.argv remains as a list when running trace.

Note that the new implementation hides internal registry and caches,
previously accessible via private attributes ``_abc_registry``,
``_abc_cache``, and ``_abc_negative_cache``. There are three debugging
helper methods that can be used instead ``_dump_registry``,
``_abc_registry_clear``, and ``_abc_caches_clear``.

- bpo-32841: Fixed `asyncio.Condition` issue which silently ignored
cancellation after notifying and cancelling a conditional lock. Patch by
Bar Harel.

- bpo-32819: ssl.match_hostname() has been simplified and no longer depends
on re and ipaddress module for wildcard and IP addresses. Error reporting
for invalid wildcards has been improved.

- bpo-19675: ``multiprocessing.Pool`` no longer leaks processes if its
initialization fails.

- bpo-32394: socket: Remove
TCP_FASTOPEN,TCP_KEEPCNT,TCP_KEEPIDLE,TCP_KEEPINTVL flags on older version
Windows during run-time.

- bpo-31787: Fixed refleaks of ``__init__()`` methods in various modules.
(Contributed by Oren Milman)

- bpo-30157: Fixed guessing quote and delimiter in csv.Sniffer.sniff() when
only the last field is quoted. Patch by Jake Davis.

- bpo-30688: Added support of ``\N{name}`` escapes in regular expressions.
Based on patch by Jonathan Eunice.

- bpo-32792: collections.ChainMap() preserves the order of the underlying
mappings.

- bpo-32775: :func:`fnmatch.translate()` no longer produces patterns which
contain set operations. Sets starting with '[' or containing '--', '&&',
'~~' or '||' will be interpreted differently in regular expressions in
future versions. Currently they emit warnings. fnmatch.translate() now
avoids producing patterns containing such sets by accident.

- bpo-32622: Implement native fast sendfile for Windows proactor event loop.

- bpo-32777: Fix a rare but potential pre-exec child process deadlock in
subprocess on POSIX systems when marking file descriptors inheritable on
exec in the child process. This bug appears to have been introduced in
3.4.

- bpo-32647: The ctypes module used to depend on indirect linking for
dlopen. The shared extension is now explicitly linked against libdl on
platforms with dl.

- bpo-32749: A :mod:`dbm.dumb` database opened with flags 'r' is now
read-only. :func:`dbm.dumb.open` with flags 'r' and 'w' no longer creates
a database if it does not exist.

- bpo-32741: Implement ``asyncio.TimerHandle.when()`` method.

- bpo-32691: Use mod_spec.parent when running modules with pdb

- bpo-32734: Fixed ``asyncio.Lock()`` safety issue which allowed acquiring
and locking the same lock multiple times, without it being free. Patch by
Bar Harel.

- bpo-32727: Do not include name field in SMTP envelope from address. Patch
by Stéphane Wirtel

- bpo-31453: Add TLSVersion constants and SSLContext.maximum_version /
minimum_version attributes. The new API wraps OpenSSL 1.1
https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_set_min_proto_version.html
feature.

- bpo-24334: Internal implementation details of ssl module were cleaned up.
The SSLSocket has one less layer of indirection. Owner and session
information are now handled by the SSLSocket and SSLObject constructor.
Channel binding implementation has been simplified.

- bpo-31848: Fix the error handling in Aifc_read.initfp() when the SSND
chunk is not found. Patch by Zackery Spytz.

- bpo-32585: Add Ttk spinbox widget to :mod:`tkinter.ttk`. Patch by Alan D
Moore.

- bpo-32512: :mod:`profile` CLI accepts `-m module_name` as an alternative
to script path.

- bpo-8525: help() on a type now displays builtin subclasses. This is
intended primarily to help with notification of more specific exception
subclasses.

Patch by Sanyam Khurana.

- bpo-31639: http.server now exposes a ThreadingHTTPServer class and uses it
when the module is run with ``-m`` to cope with web browsers pre-opening
sockets.

- bpo-29877: compileall: import ProcessPoolExecutor only when needed,
preventing hangs on low resource platforms

- bpo-32221: Various functions returning tuple containing IPv6 addresses now
omit ``%scope`` part since the same information is already encoded in
*scopeid* tuple item. Especially this speeds up :func:`socket.recvfrom`
when it receives multicast packet since useless resolving of network
interface name is omitted.

- bpo-32147: :func:`binascii.unhexlify` is now up to 2 times faster. Patch
by Sergey Fedoseev.

- bpo-30693: The TarFile class now recurses directories in a reproducible
way.

- bpo-30693: The ZipFile class now recurses directories in a reproducible
way.

- bpo-31680: Added :data:`curses.ncurses_version`.

- bpo-31908: Fix output of cover files for ``trace`` module command-line
tool. Previously emitted cover files only when ``--missing`` option was
used. Patch by Michael Selik.

- bpo-31608: Raise a ``TypeError`` instead of crashing if a
``collections.deque`` subclass returns a non-deque from ``__new__``. Patch
by Oren Milman.

- bpo-31425: Add support for sockets of the AF_QIPCRTR address family,
supported by the Linux kernel. This is used to communicate with services,
such as GPS or radio, running on Qualcomm devices. Patch by Bjorn
Andersson.

- bpo-22005: Implemented unpickling instances of
:class:`~datetime.datetime`, :class:`~datetime.date` and
:class:`~datetime.time` pickled by Python 2. ``encoding='latin1'`` should
be used for successful decoding.

- bpo-27645: :class:`sqlite3.Connection` now exposes a
:class:`~sqlite3.Connection.backup` method, if the underlying SQLite
library is at version 3.6.11 or higher. Patch by Lele Gaifax.

- bpo-16865: Support arrays >=2GiB in :mod:`ctypes`. Patch by Segev Finer.

- bpo-31508: Removed support of arguments in
`tkinter.ttk.Treeview.selection`. It was deprecated in 3.6. Use
specialized methods like `selection_set` for changing the selection.

- bpo-29456: Fix bugs in hangul normalization: u1176, u11a7 and u11c3

Documentation
-------------

- bpo-21257: Document :func:`http.client.parse_headers`.

- bpo-34764: Improve example of iter() with 2nd sentinel argument.

- bpo-35564: Explicitly set master_doc variable in conf.py for compliance
with Sphinx 2.0

- bpo-35511: Specified that profile.Profile class doesn't not support enable
or disable methods. Also, elaborated that Profile object as a context
manager is only supported in cProfile module.

- bpo-10536: Enhance the gettext docs. Patch by Éric Araujo

- bpo-35089: Remove mention of ``typing.io`` and ``typing.re``. Their types
should be imported from ``typing`` directly.

- bpo-35038: Fix the documentation about an unexisting `f_restricted`
attribute in the frame object. Patch by Stéphane Wirtel

- bpo-35042: Replace PEP XYZ by the pep role and allow to use the direct
links to the PEPs.

- bpo-35044: Fix the documentation with the role ``exc`` for the
appropriated exception. Patch by Stéphane Wirtel

- bpo-35035: Rename documentation for :mod:`email.utils` to
``email.utils.rst``.

- bpo-34967: Use app.add_object_type() instead of the deprecated Sphinx
function app.description_unit()

- bpo-34913: Add documentation about the new command line interface of the
gzip module.

- bpo-32174: chm document displays non-ASCII charaters properly on some MBCS
Windows systems.

- bpo-11233: Create availability directive for documentation. Original
patch by Georg Brandl.

- bpo-34790: Document how passing coroutines to asyncio.wait() can be
confusing.

- bpo-34552: Make clear that ``==`` operator sometimes is equivalent to
`is`. The ``<``, ``<=``, ``>`` and ``>=`` operators are only defined where
they make sense.

- bpo-28617: Fixed info in the stdtypes docs concerning the types that
support membership tests.

- bpo-20177: Migrate datetime.date.fromtimestamp to Argument Clinic. Patch
by Tim Hoffmann.

- bpo-34065: Fix wrongly written basicConfig documentation markup syntax

- bpo-33460: replaced ellipsis with correct error codes in tutorial chapter
3.

- bpo-33847: Add '@' operator entry to index.

- bpo-33409: Clarified the relationship between :pep:`538`'s
PYTHONCOERCECLOCALE and PEP 540's PYTHONUTF8 mode.

- bpo-33197: Add versionadded tag to the documentation of
ParameterKind.description

- bpo-17045: Improve the C-API doc for PyTypeObject. This includes adding
several quick-reference tables and a lot of missing slot/typedef entries.
The existing entries were also cleaned up with a slightly more consistent
format.

- bpo-33736: Improve the documentation of :func:`asyncio.open_connection`,
:func:`asyncio.start_server` and their UNIX socket counterparts.

- bpo-23859: Document that `asyncio.wait()` does not cancel its futures on
timeout.

- bpo-32436: Document :pep:`567` changes to asyncio.

- bpo-33604: Update HMAC md5 default to a DeprecationWarning, bump removal
to 3.8.

- bpo-33594: Document ``getargspec``, ``from_function`` and ``from_builtin``
as deprecated in their respective docstring, and include version since
deprecation in DeprecationWarning message.

- bpo-33503: Fix broken pypi link

- bpo-33421: Add missing documentation for ``typing.AsyncContextManager``.

- bpo-33487: BZ2file now emit a DeprecationWarning when buffering=None is
passed, the deprecation message and documentation also now explicitly
state it is deprecated since 3.0.

- bpo-33378: Add Korean language switcher for https://docs.python.org/3/

- bpo-33276: Clarify that the ``__path__`` attribute on modules cannot be
just any value.

- bpo-33201: Modernize documentation for writing C extension types.

- bpo-33195: Deprecate ``Py_UNICODE`` usage in ``c-api/arg`` document.
``Py_UNICODE`` related APIs are deprecated since Python 3.3, but it is
missed in the document.

- bpo-33126: Document PyBuffer_ToContiguous().

- bpo-27212: Modify documentation for the :func:`islice` recipe to consume
initial values up to the start index.

- bpo-28247: Update :mod:`zipapp` documentation to describe how to make
standalone applications.

- bpo-18802: Documentation changes for ipaddress. Patch by Jon Foster and
Berker Peksag.

- bpo-27428: Update documentation to clarify that ``WindowsRegistryFinder``
implements ``MetaPathFinder``. (Patch by Himanshu Lakhara)

- bpo-28124: The ssl module function ssl.wrap_socket() has been
de-emphasized and deprecated in favor of the more secure and efficient
SSLContext.wrap_socket() method.

- bpo-17232: Clarify docs for -O and -OO. Patch by Terry Reedy.

- bpo-32436: Add documentation for the contextvars module (PEP 567).

- bpo-32800: Update link to w3c doc for xml default namespaces.

- bpo-11015: Update :mod:`test.support` documentation.

- bpo-32613: Update the faq/windows.html to use the py command from PEP 397
instead of python.

- bpo-8722: Document :meth:`__getattr__` behavior when property :meth:`get`
method raises :exc:`AttributeError`.

- bpo-32614: Modify RE examples in documentation to use raw strings to
prevent :exc:`DeprecationWarning` and add text to REGEX HOWTO to highlight
the deprecation.

- bpo-20709: Remove the paragraph where we explain that os.utime() does not
support a directory as path under Windows. Patch by Jan-Philip Gehrcke

- bpo-32722: Remove the bad example in the tutorial of the Generator
Expression. Patch by Stéphane Wirtel

- bpo-31972: Improve docstrings for `pathlib.PurePath` subclasses.

- bpo-30607: Use the externalized ``python-docs-theme`` package when
building the documentation.

- bpo-8243: Add a note about curses.addch and curses.addstr exception
behavior when writing outside a window, or pad.

- bpo-32337: Update documentation related with ``dict`` order.

- bpo-25041: Document ``AF_PACKET`` in the :mod:`socket` module.

- bpo-31432: Clarify meaning of CERT_NONE, CERT_OPTIONAL, and CERT_REQUIRED
flags for ssl.SSLContext.verify_mode.

Tests
-----

- bpo-35772: Fix sparse file tests of test_tarfile on ppc64 with the tmpfs
filesystem. Fix the function testing if the filesystem supports sparse
files: create a file which contains data and "holes", instead of creating
a file which contains no data. tmpfs effective block size is a page size
(tmpfs lives in the page cache). RHEL uses 64 KiB pages on aarch64, ppc64,
ppc64le, only s390x and x86_64 use 4 KiB pages, whereas the test punch
holes of 4 KiB.

- bpo-35045: Make ssl tests less strict and also accept TLSv1 as system
default. The changes unbreaks test_min_max_version on Fedora 29.

- bpo-32710: ``test_asyncio/test_sendfile.py`` now resets the event loop
policy using :func:`tearDownModule` as done in other tests, to prevent a
warning when running tests on Windows.

- bpo-33717: test.pythoninfo now logs information of all clocks, not only
time.time() and time.perf_counter().

- bpo-35488: Add a test to pathlib's Path.match() to verify it does not
support glob-style ** recursive pattern matching.

- bpo-31731: Fix a race condition in ``check_interrupted_write()`` of
test_io: create directly the thread with SIGALRM signal blocked, rather
than blocking the signal later from the thread. Previously, it was
possible that the thread gets the signal before the signal is blocked.

- bpo-35424: Fix test_multiprocessing_main_handling: use
:class:`multiprocessing.Pool` with a context manager and then explicitly
join the pool.

- bpo-35519: Rename :mod:`test.bisect` module to :mod:`test.bisect_cmd` to
avoid conflict with :mod:`bisect` module when running directly a test like
``./python Lib/test/test_xmlrpc.py``.

- bpo-35513: Replace :func:`time.time` with :func:`time.monotonic` in tests
to measure time delta.

- bpo-34279: :func:`test.support.run_unittest` no longer raise
:exc:`TestDidNotRun` if the test result contains skipped tests. The
exception is now only raised if no test have been run and no test have
been skipped.

- bpo-35412: Add testcase to ``test_future4``: check unicode literal.

- bpo-26704: Added test demonstrating double-patching of an instance method.
Patch by Anthony Sottile.

- bpo-33725: test_multiprocessing_fork may crash on recent versions of
macOS. Until the issue is resolved, skip the test on macOS.

- bpo-35352: Modify test_asyncio to use the certificate set from the test
directory.

- bpo-35317: Fix ``mktime()`` overflow error in ``test_email``: run
``test_localtime_daylight_true_dst_true()`` and
``test_localtime_daylight_false_dst_true()`` with a specific timezone.

- bpo-21263: After several reports that test_gdb does not work properly on
macOS and since gdb is not shipped by default anymore, test_gdb is now
skipped on macOS when LLVM Clang has been used to compile Python. Patch by
Lysandros Nikolaou

- bpo-34279: regrtest issue a warning when no tests have been executed in a
particular test file. Also, a new final result state is issued if no test
have been executed across all test files. Patch by Pablo Galindo.

- bpo-34962: make docstest in Doc now passes., and is enforced in CI

- bpo-23596: Use argparse for the command line of the gzip module. Patch by
Antony Lee

- bpo-34537: Fix ``test_gdb.test_strings()`` when ``LC_ALL=C`` and GDB was
compiled with Python 3.6 or earlier.

- bpo-34587: test_socket: Remove RDSTest.testCongestion(). The test tries to
fill the receiver's socket buffer and expects an error. But the RDS
protocol doesn't require that. Moreover, the Linux implementation of RDS
expects that the producer of the messages reduces its rate, it's not the
role of the receiver to trigger an error. The test fails on Fedora 28 by
design, so just remove it.

- bpo-34661: Fix test_shutil if unzip doesn't support -t.

- bpo-34200: Fixed non-deterministic flakiness of test_pkg by not using the
scary test.support.module_cleanup() logic to save and restore sys.modules
contents between test cases.

- bpo-34569: The experimental PEP 554 data channels now correctly pass
negative PyLong objects between subinterpreters on 32-bit systems. Patch
by Michael Felt.

- bpo-34594: Fix usage of hardcoded ``errno`` values in the tests.

- bpo-34579: Fix test_embed for AIX Patch by Michael Felt

- bpo-34542: Use 3072 RSA keys and SHA-256 signature for test certs and
keys.

- bpo-11193: Remove special condition for AIX in
`test_subprocess.test_undecodable_env`

- bpo-34347: Fix `test_utf8_mode.test_cmd_line` for AIX

- bpo-34490: On AIX with AF_UNIX family sockets getsockname() does not
provide 'sockname', so skip calls to transport.get_extra_info('sockname')

- bpo-34391: Fix ftplib test for TLS 1.3 by reading from data socket.

- bpo-11192: Fix `test_socket` on AIX 6.1 and later IPv6 zone id supports
only supported by inet_pton6_zone() Switch to runtime-based
platform.system() to establish current platform rather than build-time
based sys.platform()

- bpo-34399: Update all RSA keys and DH params to use at least 2048 bits.

- bpo-34373: Fix ``test_mktime`` and ``test_pthread_getcpuclickid`` tests
for AIX Add range checking for ``_PyTime_localtime`` for AIX Patch by
Michael Felt

- bpo-11191: Skip the distutils test 'test_search_cpp' when using XLC as
compiler patch by aixtools (Michael Felt)

- Improved an error message when mock assert_has_calls fails.

- bpo-33746: Fix test_unittest when run in verbose mode.

- bpo-33901: Fix test_dbm_gnu on macOS with gdbm 1.15: add a larger value to
make sure that the file size changes.

- bpo-33873: Fix a bug in ``regrtest`` that caused an extra test to run if
--huntrleaks/-R was used. Exit with error in case that invalid parameters
are specified to --huntrleaks/-R (at least one warmup run and one
repetition must be used).

- bpo-33562: Check that a global asyncio event loop policy is not left
behind by any tests.

- bpo-33655: Ignore test_posix_fallocate failures on BSD platforms that
might be due to running on ZFS.

- bpo-32962: Fixed test_gdb when Python is compiled with flags -mcet
-fcf-protection -O0.

- bpo-33358: Fix ``test_embed.test_pre_initialization_sys_options()`` when
the interpreter is built with ``--enable-shared``.

- bpo-32872: Avoid regrtest compatibility issue with namespace packages.

- bpo-32517: Fix failing ``test_asyncio`` on macOS 10.12.2+ due to transport
of ``KqueueSelector`` loop was not being closed.

- bpo-32663: Making sure the `SMTPUTF8SimTests` class of tests gets run in
test_smtplib.py.

- bpo-27643: Test_C test case needs "signed short" bitfields, but the IBM
XLC compiler (on AIX) does not support this Skip the code and test when
AIX and XLC are used

Applicable to Python2-2.7 and later

- bpo-19417: Add test_bdb.py.

- bpo-31809: Add tests to verify connection with secp ECDH curves.

Build
-----

- bpo-34691: The _contextvars module is now built into the core Python
library on Windows.

- bpo-35683: Improved Azure Pipelines build steps and now verifying layouts
correctly

- bpo-35642: Remove asynciomodule.c from pythoncore.vcxproj

- bpo-35550: Fix incorrect Solaris #ifdef checks to look for __sun && __SVR4
instead of sun when compiling.

- bpo-35499: ``make profile-opt`` no longer replaces ``CFLAGS_NODIST`` with
``CFLAGS``. It now adds profile-guided optimization (PGO) flags to
``CFLAGS_NODIST``: existing ``CFLAGS_NODIST`` flags are kept.

- bpo-35257: Avoid leaking the linker flags from Link Time Optimizations
(LTO) into distutils when compiling C extensions.

- bpo-35351: When building Python with clang and LTO, LTO flags are no
longer passed into CFLAGS to build third-party C extensions through
distutils.

- bpo-35139: Fix a compiler error when statically linking `pyexpat` in
`Modules/Setup`.

- bpo-35059: PCbuild: Set InlineFunctionExpansion to OnlyExplicitInline
("/Ob1" option) in pyproject.props in Debug mode to expand functions
marked as inline. This change should make Python compiled in Debug mode a
little bit faster on Windows.

- bpo-35011: Restores the use of pyexpatns.h to isolate our embedded copy of
the expat C library so that its symbols do not conflict at link or dynamic
loading time with an embedding application or other extension modules with
their own version of libexpat.

- bpo-28015: Have --with-lto works correctly with clang.

- bpo-34765: Update the outdated install-sh file to the latest revision from
automake v1.16.1

- bpo-34585: Check for floating-point byte order in configure.ac using
compilation tests instead of executing code, so that these checks work in
cross-compiled builds.

- bpo-34710: Fixed SSL module build with OpenSSL & pedantic CFLAGS.

- bpo-34582: Add JUnit XML output for regression tests and update Azure
DevOps builds.

- bpo-34081: Make Sphinx warnings as errors in the Docs Makefile.

- bpo-34555: Fix for case where it was not possible to have both
``HAVE_LINUX_VM_SOCKETS_H`` and ``HAVE_SOCKADDR_ALG`` be undefined.

- bpo-33015: Fix an undefined behaviour in the pthread implementation of
:c:func:`PyThread_start_new_thread`: add a function wrapper to always
return ``NULL``.

- bpo-34245: The Python shared library is now installed with write
permission (mode 0755), which is the standard way of installing such
libraries.

- bpo-34121: Fix detection of C11 atomic support on clang.

- bpo-32430: Rename Modules/Setup.dist to Modules/Setup, and remove the
necessity to copy the former manually to the latter when updating the
local source tree.

- bpo-30345: Add -g to LDFLAGS when compiling with LTO to get debug symbols.

- bpo-5755: Move ``-Wstrict-prototypes`` option to ``CFLAGS_NODIST`` from
``OPT``. This option emitted annoying warnings when building extension
modules written in C++.

- bpo-33614: Ensures module definition files for the stable ABI on Windows
are correctly regenerated.

- bpo-33648: The --with-c-locale-warning configuration flag has been
removed. It has had no effect for about a year.

- bpo-33522: Enable CI builds on Visual Studio Team Services at
https://python.visualstudio.com/cpython

- bpo-33512: configure's check for "long double" has been simplified

- bpo-33483: C compiler is now correctly detected from the standard
environment variables. --without-gcc and --with-icc options have been
removed.

- bpo-33394: Enable the verbose build for extension modules, when GNU make
is passed macros on the command line.

- bpo-33393: Update config.guess and config.sub files.

- bpo-33377: Add new triplets for mips r6 and riscv variants (used in
extension suffixes).

- bpo-32232: By default, modules configured in `Modules/Setup` are no longer
built with `-DPy_BUILD_CORE`. Instead, modules that specifically need that
preprocessor definition include it in their individual entries.

- bpo-33182: The embedding tests can once again be built with clang 6.0

- bpo-33163: Upgrade pip to 9.0.3 and setuptools to v39.0.1.

- bpo-33012: gcc 8 has added a new warning heuristic to detect invalid
function casts and a stock python build seems to hit that warning quite
often. The most common is the cast of a METH_NOARGS function (that uses
just one argument) to a PyCFunction. Fix this by adding a dummy argument
to all functions that implement METH_NOARGS.

- bpo-32898: Fix the python debug build when using COUNT_ALLOCS.

- bpo-29442: Replace optparse with argparse in setup.py

Windows
-------

- bpo-35890: Fix API calling consistency of GetVersionEx and wcstok.

- bpo-32560: The ``py`` launcher now forwards its ``STARTUPINFO`` structure
to child processes.

- bpo-35854: Fix EnvBuilder and --symlinks in venv on Windows

- bpo-35811: Avoid propagating venv settings when launching via py.exe

- bpo-35797: Fix default executable used by the multiprocessing module

- bpo-35758: Allow building on ARM with MSVC.

- bpo-29734: Fix handle leaks in os.stat on Windows.

- bpo-35596: Use unchecked PYCs for the embeddable distro to avoid zipimport
restrictions.

- bpo-35596: Fix vcruntime140.dll being added to embeddable distro multiple
times.

- bpo-35402: Update Windows build to use Tcl and Tk 8.6.9

- bpo-35401: Updates Windows build to OpenSSL 1.1.0j

- bpo-34977: venv on Windows will now use a python.exe redirector rather
than copying the actual binaries from the base environment.

- bpo-34977: Adds support for building a Windows App Store package

- bpo-35067: Remove _distutils_findvs module and use vswhere.exe instead.

- bpo-32557: Allow shutil.disk_usage to take a file path on Windows

- bpo-34770: Fix a possible null pointer dereference in pyshellext.cpp.

- bpo-34603: Fix returning structs from functions produced by MSVC

- bpo-34581: Guard MSVC-specific code in socketmodule.c with ``#ifdef
_MSC_VER``.

- bpo-34532: Fixes exit code of list version arguments for py.exe.

- bpo-34062: Fixed the '--list' and '--list-paths' arguments for the py.exe
launcher

- bpo-34225: Ensure INCLUDE and LIB directories do not end with a backslash.

- bpo-34011: A suite of code has been changed which copied across DLLs and
init.tcl from the running Python location into a venv being created. These
copies are needed only when running from a Python source build, and the
copying code is now only run when that is the case, rather than whenever a
venv is created.

- bpo-34006: Revert line length limit for Windows help docs. The line-length
limit is not needed because the pages appear in a separate app rather than
on a browser tab. It can also interact badly with the DPI setting.

- bpo-31546: Restore running PyOS_InputHook while waiting for user input at
the prompt. The restores integration of interactive GUI windows (such as
Matplotlib figures) with the prompt on Windows.

- bpo-30237: Output error when ReadConsole is canceled by
CancelSynchronousIo instead of crashing.

- bpo-33895: GIL is released while calling functions that acquire Windows
loader lock.

- bpo-33720: Reduces maximum marshal recursion depth on release builds.

- bpo-29097: Fix bug where :meth:`datetime.fromtimestamp` erroneously throws
an :exc:`OSError` on Windows for values between 0 and 86400. Patch by
Ammar Askar.

- bpo-33316: PyThread_release_lock always fails

- bpo-33184: Update Windows installer to use OpenSSL 1.1.0h.

- bpo-32890: Fix usage of GetLastError() instead of errno in os.execve() and
os.truncate().

- bpo-33016: Fix potential use of uninitialized memory in
nt._getfinalpathname

- bpo-32903: Fix a memory leak in os.chdir() on Windows if the current
directory is set to a UNC path.

- bpo-32901: Update Tcl and Tk versions to 8.6.8

- bpo-31966: Fixed WindowsConsoleIO.write() for writing empty data.

- bpo-32409: Ensures activate.bat can handle Unicode contents.

- bpo-32457: Improves handling of denormalized executable path when
launching Python.

- bpo-32370: Use the correct encoding for ipconfig output in the uuid
module. Patch by Segev Finer.

- bpo-29248: Fix :func:`os.readlink` on Windows, which was mistakenly
treating the ``PrintNameOffset`` field of the reparse data buffer as a
number of characters instead of bytes. Patch by Craig Holmquist and SSE4.

- bpo-1104: Correctly handle string length in
``msilib.SummaryInfo.GetProperty()`` to prevent it from truncating the
last character.

macOS
-----

- bpo-35401: Update macOS installer to use OpenSSL 1.1.0j.

- bpo-35025: Properly guard the use of the ``CLOCK_GETTIME`` et al. macros
in ``timemodule`` on macOS.

- bpo-24658: On macOS, fix reading from and writing into a file with a size
larger than 2 GiB.

- bpo-34405: Update to OpenSSL 1.1.0i for macOS installer builds.

- bpo-33635: In macOS stat on some file descriptors (/dev/fd/3 f.e) will
result in bad file descriptor OSError. Guard against this exception was
added in is_dir, is_file and similar methods. DirEntry.is_dir can also
throw this exception so _RecursiveWildcardSelector._iterate_directories
was also extended with the same error ignoring pattern.

- bpo-13631: The .editrc file in user's home directory is now processed
correctly during the readline initialization through editline emulation on
macOS.

- bpo-33184: Update macOS installer build to use OpenSSL 1.1.0h.

- bpo-32726: Build and link with private copy of Tcl/Tk 8.6 for the macOS
10.6+ installer. The 10.9+ installer variant already does this. This
means that the Python 3.7 provided by the python.org macOS installers no
longer need or use any external versions of Tcl/Tk, either system-provided
or user-installed, such as ActiveTcl.

- bpo-32901: Update macOS 10.9+ installer to Tcl/Tk 8.6.8.

- bpo-31903: In :mod:`_scproxy`, drop the GIL when calling into
``SystemConfiguration`` to avoid deadlocks.

IDLE
----

- bpo-35770: IDLE macosx deletes Options => Configure IDLE. It previously
deleted Window => Zoom Height by mistake. (Zoom Height is now on the
Options menu). On Mac, the settings dialog is accessed via Preferences on
the IDLE menu.

- bpo-35769: Change IDLE's new file name from 'Untitled' to 'untitled'

- bpo-35660: Fix imports in idlelib.window.

- bpo-35641: Proper format `calltip` when the function has no docstring.

- bpo-33987: Use ttk Frame for ttk widgets.

- bpo-34055: Fix erroneous 'smart' indents and newlines in IDLE Shell.

- bpo-35591: Find Selection now works when selection not found.

- bpo-35196: Speed up squeezer line counting.

- bpo-35598: Update config_key: use PEP 8 names and ttk widgets, make some
objects global, and add tests.

- bpo-28097: Add Previous/Next History entries to Shell menu.

- bpo-35208: Squeezer now properly counts wrapped lines before newlines.

- bpo-35555: Gray out Code Context menu entry when it's not applicable.

- bpo-35521: Document the IDLE editor code context feature. Add some
internal references within the IDLE doc.

- bpo-22703: The Code Context menu label now toggles between Show/Hide Code
Context. The Zoom Height menu now toggles between Zoom/Restore Height.
Zoom Height has moved from the Window menu to the Options menu.

- bpo-35213: Where appropriate, use 'macOS' in idlelib.

- bpo-34864: On macOS, warn if the system preference "Prefer tabs when
opening documents" is set to "Always".

- bpo-34864: Document two IDLE on MacOS issues. The System Preferences Dock
"prefer tabs always" setting disables some IDLE features. Menus are a bit
different than as described for Windows and Linux.

- bpo-35202: Remove unused imports from lib/idlelib

- bpo-33000: Document that IDLE's shell has no line limit. A program that
runs indefinitely can overfill memory.

- bpo-23220: Explain how IDLE's Shell displays output.

- bpo-35099: Improve the doc about IDLE running user code. The section is
renamed from "IDLE -- console differences" is renamed "Running user code".
It mostly covers the implications of using custom sys.stdxxx objects.

- bpo-35097: Add IDLE doc subsection explaining editor windows. Topics
include opening, title and status bar, .py* extension, and running.

- bpo-35093: Document the IDLE document viewer in the IDLE doc. Add a
paragraph in "Help and preferences", "Help sources" subsection.

- bpo-35088: Update idlelib.help.copy_string docstring. We now use git and
backporting instead of hg and forward merging.

- bpo-35087: Update idlelib help files for the current doc build. The main
change is the elimination of chapter-section numbers.

- bpo-34548: Use configured color theme for read-only text views.

- bpo-1529353: Enable "squeezing" of long outputs in the shell, to avoid
performance degradation and to clean up the history without losing it.
Squeezed outputs may be copied, viewed in a separate window, and
"unsqueezed".

- bpo-34047: Fixed mousewheel scrolling direction on macOS.

- bpo-34275: Make IDLE calltips always visible on Mac. Some MacOS-tk
combinations need .update_idletasks(). Patch by Kevin Walzer.

- bpo-34120: Fix unresponsiveness after closing certain windows and dialogs.

- bpo-33975: Avoid small type when running htests. Since part of the purpose
of human-viewed tests is to determine that widgets look right, it is
important that they look the same for testing as when running IDLE.

- bpo-33905: Add test for idlelib.stackview.StackBrowser.

- bpo-33924: Change mainmenu.menudefs key 'windows' to 'window'. Every other
menudef key is lowercase version of main menu entry.

- bpo-33906: Rename idlelib.windows as window Match Window on the main menu
and remove last plural module name.

- bpo-33917: Fix and document idlelib/idle_test/template.py. The revised
file compiles, runs, and tests OK. idle_test/README.txt explains how to
use it to create new IDLE test files.

- bpo-33904: IDLE: In rstrip, rename class RstripExtension as Rstrip

- bpo-33907: For consistency and clarity, rename an IDLE module and classes.
Module calltips and its class CallTips are now calltip and Calltip. In
module calltip_w, class CallTip is now CalltipWindow.

- bpo-33856: Add "help" in the welcome message of IDLE

- bpo-33839: IDLE: refactor ToolTip and CallTip and add documentation and
tests

- bpo-33855: Minimally test all IDLE modules. Add missing files, import
module, instantiate classes, and check coverage. Check existing files.

- bpo-33656: On Windows, add API call saying that tk scales for DPI. On
Windows 8.1+ or 10, with DPI compatibility properties of the Python binary
unchanged, and a monitor resolution greater than 96 DPI, this should make
text and lines sharper. It should otherwise have no effect.

- bpo-33768: Clicking on a context line moves that line to the top of the
editor window.

- bpo-33763: IDLE: Use read-only text widget for code context instead of
label widget.

- bpo-33664: Scroll IDLE editor text by lines. Previously, the mouse wheel
and scrollbar slider moved text by a fixed number of pixels, resulting in
partial lines at the top of the editor box. The change also applies to
the shell and grep output windows, but not to read-only text views.

- bpo-33679: Enable theme-specific color configuration for Code Context. Use
the Highlights tab to see the setting for built-in themes or add settings
to custom themes.

- bpo-33642: Display up to maxlines non-blank lines for Code Context. If
there is no current context, show a single blank line.

- bpo-33628: IDLE: Cleanup codecontext.py and its test.

- bpo-33564: IDLE's code context now recognizes async as a block opener.

- bpo-21474: Update word/identifier definition from ascii to unicode. In
text and entry boxes, this affects selection by double-click, movement
left/right by control-left/right, and deletion left/right by
control-BACKSPACE/DEL.

- bpo-33204: IDLE: consistently color invalid string prefixes. A 'u' string
prefix cannot be paired with either 'r' or 'f'. Consistently color as much
of the prefix, starting at the right, as is valid. Revise and extend
colorizer test.

- bpo-32984: Set ``__file__`` while running a startup file. Like Python,
IDLE optionally runs one startup file in the Shell window before
presenting the first interactive input prompt. For IDLE, ``-s`` runs a
file named in environmental variable :envvar:`IDLESTARTUP` or
:envvar:`PYTHONSTARTUP`; ``-r file`` runs ``file``. Python sets
``__file__`` to the startup file name before running the file and unsets
it before the first prompt. IDLE now does the same when run normally,
without the ``-n`` option.

- bpo-32940: Simplify and rename StringTranslatePseudoMapping in pyparse.

- bpo-32916: Change ``str`` to ``code`` in pyparse.

- bpo-32905: Remove unused code in pyparse module.

- bpo-32874: Add tests for pyparse.

- bpo-32837: Using the system and place-dependent default encoding for
open() is a bad idea for IDLE's system and location-independent files.

- bpo-32826: Add "encoding=utf-8" to open() in IDLE's test_help_about. GUI
test test_file_buttons() only looks at initial ascii-only lines, but
failed on systems where open() defaults to 'ascii' because readline()
internally reads and decodes far enough ahead to encounter a non-ascii
character in CREDITS.txt.

- bpo-32831: Add docstrings and tests for codecontext.

- bpo-32765: Update configdialog General tab docstring to add new widgets to
the widget list.

Tools/Demos
-----------

- bpo-35884: Add a benchmark script for timing various ways to access
variables: ``Tools/scripts/var_access_benchmark.py``.

- bpo-34989: python-gdb.py now handles errors on computing the line number
of a Python frame.

- bpo-20260: Argument Clinic now has non-bitwise unsigned int converters.

- bpo-32962: python-gdb now catches ``UnicodeDecodeError`` exceptions when
calling ``string()``.

- bpo-32962: python-gdb now catches ValueError on read_var(): when Python
has no debug symbols for example.

- bpo-33189: :program:`pygettext.py` now recognizes only literal strings as
docstrings and translatable strings, and rejects bytes literals and
f-string expressions.

- bpo-31920: Fixed handling directories as arguments in the ``pygettext``
script. Based on patch by Oleg Krasnikov.

- bpo-29673: Fix pystackv and pystack gdbinit macros.

- bpo-25427: Remove the pyvenv script in favor of ``python3 -m venv`` in
order to lower confusion as to what Python interpreter a virtual
environment will be created for.

- bpo-32885: Add an ``-n`` flag for ``Tools/scripts/pathfix.py`` to disable
automatic backup creation (files with ``~`` suffix).

- bpo-32222: Fix pygettext not extracting docstrings for functions with type
annotated arguments. Patch by Toby Harradine.

- bpo-31583: Fix 2to3 for using with --add-suffix option but without
--output-dir option for relative path to files in current directory.

C API
-----

- bpo-35713: The :c:func:`PyByteArray_Init` and :c:func:`PyByteArray_Fini`
functions have been removed. They did nothing since Python 2.7.4 and
Python 3.2.0, were excluded from the limited API (stable ABI), and were
not documented.

- bpo-33817: Fixed :c:func:`_PyBytes_Resize` for empty bytes objects.

- bpo-35322: Fix memory leak in :c:func:`PyUnicode_EncodeLocale` and
:c:func:`PyUnicode_EncodeFSDefault` on error handling.

- bpo-35059: The following C macros have been converted to static inline
functions: :c:func:`Py_INCREF`, :c:func:`Py_DECREF`, :c:func:`Py_XINCREF`,
:c:func:`Py_XDECREF`, :c:func:`PyObject_INIT`,
:c:func:`PyObject_INIT_VAR`.

- bpo-35296: ``make install`` now also installs the internal API:
``Include/internal/*.h`` header files.

- bpo-35081: Internal APIs surrounded by ``#ifdef Py_BUILD_CORE`` have been
moved from ``Include/*.h`` headers to new header files
``Include/internal/pycore_*.h``.

- bpo-35259: Conditionally declare :c:func:`Py_FinalizeEx()` (new in 3.6)
based on Py_LIMITED_API. Patch by Arthur Neufeld.

- bpo-35081: The :c:func:`_PyObject_GC_TRACK` and
:c:func:`_PyObject_GC_UNTRACK` macros have been removed from the public C
API.

- bpo-35134: Creation of a new ``Include/cpython/`` subdirectory.

- bpo-34725: Adds _Py_SetProgramFullPath so embedders may override
sys.executable

- bpo-34910: Ensure that :c:func:`PyObject_Print` always returns ``-1`` on
error. Patch by Zackery Spytz.

- bpo-34523: Py_DecodeLocale() and Py_EncodeLocale() now use the UTF-8
encoding on Windows if Py_LegacyWindowsFSEncodingFlag is zero.

- bpo-34193: Fix pluralization in TypeError messages in getargs.c and
typeobject.c: '1 argument' instead of '1 arguments' and '1 element'
instead of '1 elements'.

- bpo-34127: Return grammatically correct error message based on argument
count. Patch by Karthikeyan Singaravelan.

- bpo-23927: Fixed :exc:`SystemError` in
:c:func:`PyArg_ParseTupleAndKeywords` when the ``w*`` format unit is used
for optional parameter.

- bpo-32455: Added :c:func:`PyCompile_OpcodeStackEffectWithJump`.

- bpo-34008: Py_Main() can again be called after Py_Initialize(), as in
Python 3.6.

- bpo-32500: Fixed error messages for :c:func:`PySequence_Size`,
:c:func:`PySequence_GetItem`, :c:func:`PySequence_SetItem` and
:c:func:`PySequence_DelItem` called with a mapping and
:c:func:`PyMapping_Size` called with a sequence.

- bpo-33818: :c:func:`PyExceptionClass_Name` will now return ``const char
*`` instead of ``char *``.

- bpo-33042: Embedding applications may once again call
PySys_ResetWarnOptions, PySys_AddWarnOption, and PySys_AddXOption prior to
calling Py_Initialize.

- bpo-32374: Document that m_traverse for multi-phase initialized modules
can be called with m_state=NULL, and add a sanity check

- bpo-30863: :c:func:`PyUnicode_AsWideChar` and
:c:func:`PyUnicode_AsWideCharString` no longer cache the ``wchar_t*``
representation of string objects.

What's New in Python 3.7.0 final?
=================================

*Release date: 2018-06-27*

Library
-------

- bpo-33851: Fix :func:`ast.get_docstring` for a node that lacks a
docstring.

C API
-----

- bpo-33932: Calling Py_Initialize() twice does nothing, instead of failing
with a fatal error: restore the Python 3.6 behaviour.

What's New in Python 3.7.0 release candidate 1?
===============================================

*Release date: 2018-06-12*