:mod:`types` --- Dynamic type creation and names for built-in types
===================================================================
.. module:: types
:synopsis: Names for built-in types.
**Source code:** :source:`Lib/types.py`
--------------
This module defines utility functions to assist in dynamic creation of
new types.
It also defines names for some object types that are used by the standard
Python interpreter, but not exposed as builtins like :class:`int` or
:class:`str` are.
Finally, it provides some additional type-related utility classes and functions
that are not fundamental enough to be builtins.
Dynamic Type Creation
---------------------
.. function:: new_class(name, bases=(), kwds=None, exec_body=None)
Creates a class object dynamically using the appropriate metaclass.
The first three arguments are the components that make up a class
definition header: the class name, the base classes (in order), the
keyword arguments (such as ``metaclass``).
The *exec_body* argument is a callback that is used to populate the
freshly created class namespace. It should accept the class namespace
as its sole argument and update the namespace directly with the class
contents. If no callback is provided, it has the same effect as passing
in ``lambda ns: None``.
.. versionadded:: 3.3
.. function:: prepare_class(name, bases=(), kwds=None)
Calculates the appropriate metaclass and creates the class namespace.
The arguments are the components that make up a class definition header:
the class name, the base classes (in order) and the keyword arguments
(such as ``metaclass``).
The return value is a 3-tuple: ``metaclass, namespace, kwds``
*metaclass* is the appropriate metaclass, *namespace* is the
prepared class namespace and *kwds* is an updated copy of the passed
in *kwds* argument with any ``'metaclass'`` entry removed. If no *kwds*
argument is passed in, this will be an empty dict.
.. versionadded:: 3.3
.. versionchanged:: 3.6
The default value for the ``namespace`` element of the returned
tuple has changed. Now an insertion-order-preserving mapping is
used when the metaclass does not have a ``__prepare__`` method.
.. seealso::
:ref:`metaclasses`
Full details of the class creation process supported by these functions
:pep:`3115` - Metaclasses in Python 3000
Introduced the ``__prepare__`` namespace hook
.. function:: resolve_bases(bases)
Resolve MRO entries dynamically as specified by :pep:`560`.
This function looks for items in *bases* that are not instances of
:class:`type`, and returns a tuple where each such object that has
an ``__mro_entries__`` method is replaced with an unpacked result of
calling this method. If a *bases* item is an instance of :class:`type`,
or it doesn't have an ``__mro_entries__`` method, then it is included in
the return tuple unchanged.
.. versionadded:: 3.7
.. seealso::
:pep:`560` - Core support for typing module and generic types
Standard Interpreter Types
--------------------------
This module provides names for many of the types that are required to
implement a Python interpreter. It deliberately avoids including some of
the types that arise only incidentally during processing such as the
``listiterator`` type.
Typical use of these names is for :func:`isinstance` or
:func:`issubclass` checks.
If you instantiate any of these types, note that signatures may vary between Python versions.
Standard names are defined for the following types:
.. data:: NoneType
The type of :data:`None`.
.. versionadded:: 3.10
.. data:: FunctionType
LambdaType
The type of user-defined functions and functions created by
:keyword:`lambda` expressions.
.. audit-event:: function.__new__ code types.FunctionType
The audit event only occurs for direct instantiation of function objects,
and is not raised for normal compilation.
.. data:: GeneratorType
The type of :term:`generator`-iterator objects, created by
generator functions.
.. data:: CoroutineType
The type of :term:`coroutine` objects, created by
:keyword:`async def` functions.
.. versionadded:: 3.5
.. data:: AsyncGeneratorType
The type of :term:`asynchronous generator`-iterator objects, created by
asynchronous generator functions.
.. versionadded:: 3.6
.. class:: CodeType(**kwargs)
.. index:: builtin: compile
The type for code objects such as returned by :func:`compile`.
.. audit-event:: code.__new__ code,filename,name,argcount,posonlyargcount,kwonlyargcount,nlocals,stacksize,flags types.CodeType
Note that the audited arguments may not match the names or positions
required by the initializer. The audit event only occurs for direct
instantiation of code objects, and is not raised for normal compilation.
.. method:: CodeType.replace(**kwargs)
Return a copy of the code object with new values for the specified fields.
.. versionadded:: 3.8
.. data:: CellType
The type for cell objects: such objects are used as containers for
a function's free variables.
.. versionadded:: 3.8
.. data:: MethodType
The type of methods of user-defined class instances.
.. data:: BuiltinFunctionType
BuiltinMethodType
The type of built-in functions like :func:`len` or :func:`sys.exit`, and
methods of built-in classes. (Here, the term "built-in" means "written in
C".)
.. data:: WrapperDescriptorType
The type of methods of some built-in data types and base classes such as
:meth:`object.__init__` or :meth:`object.__lt__`.
.. versionadded:: 3.7
.. data:: MethodWrapperType
The type of *bound* methods of some built-in data types and base classes.
For example it is the type of :code:`object().__str__`.
.. versionadded:: 3.7
.. data:: NotImplementedType
The type of :data:`NotImplemented`.
.. versionadded:: 3.10
.. data:: MethodDescriptorType
The type of methods of some built-in data types such as :meth:`str.join`.
.. versionadded:: 3.7
.. data:: ClassMethodDescriptorType
The type of *unbound* class methods of some built-in data types such as
``dict.__dict__['fromkeys']``.
.. versionadded:: 3.7
.. class:: ModuleType(name, doc=None)
The type of :term:`modules <module>`. The constructor takes the name of the
module to be created and optionally its :term:`docstring`.
.. note::
Use :func:`importlib.util.module_from_spec` to create a new module if you
wish to set the various import-controlled attributes.
.. attribute:: __doc__
The :term:`docstring` of the module. Defaults to ``None``.
.. attribute:: __loader__
The :term:`loader` which loaded the module. Defaults to ``None``.
This attribute is to match :attr:`importlib.machinery.ModuleSpec.loader`
as stored in the :attr:`__spec__` object.
.. note::
A future version of Python may stop setting this attribute by default.
To guard against this potential change, preferably read from the
:attr:`__spec__` attribute instead or use
``getattr(module, "__loader__", None)`` if you explicitly need to use
this attribute.
.. versionchanged:: 3.4
Defaults to ``None``. Previously the attribute was optional.
.. attribute:: __name__
The name of the module. Expected to match
:attr:`importlib.machinery.ModuleSpec.name`.
.. attribute:: __package__
Which :term:`package` a module belongs to. If the module is top-level
(i.e. not a part of any specific package) then the attribute should be set
to ``''``, else it should be set to the name of the package (which can be
:attr:`__name__` if the module is a package itself). Defaults to ``None``.
This attribute is to match :attr:`importlib.machinery.ModuleSpec.parent`
as stored in the :attr:`__spec__` object.
.. note::
A future version of Python may stop setting this attribute by default.
To guard against this potential change, preferably read from the
:attr:`__spec__` attribute instead or use
``getattr(module, "__package__", None)`` if you explicitly need to use
this attribute.
.. versionchanged:: 3.4
Defaults to ``None``. Previously the attribute was optional.
.. attribute:: __spec__
A record of the module's import-system-related state. Expected to be an
instance of :class:`importlib.machinery.ModuleSpec`.
.. versionadded:: 3.4
.. data:: EllipsisType
The type of :data:`Ellipsis`.
.. versionadded:: 3.10
.. class:: GenericAlias(t_origin, t_args)
The type of :ref:`parameterized generics <types-genericalias>` such as
``list[int]``.
``t_origin`` should be a non-parameterized generic class, such as ``list``,
``tuple`` or ``dict``. ``t_args`` should be a :class:`tuple` (possibly of
length 1) of types which parameterize ``t_origin``::
>>> from types import GenericAlias
>>> list[int] == GenericAlias(list, (int,))
True
>>> dict[str, int] == GenericAlias(dict, (str, int))
True
.. versionadded:: 3.9
.. versionchanged:: 3.9.2
This type can now be subclassed.
.. class:: UnionType
The type of :ref:`union type expressions<types-union>`.
.. versionadded:: 3.10
.. class:: TracebackType(tb_next, tb_frame, tb_lasti, tb_lineno)
The type of traceback objects such as found in ``sys.exc_info()[2]``.
See :ref:`the language reference <traceback-objects>` for details of the
available attributes and operations, and guidance on creating tracebacks
dynamically.
.. data:: FrameType
The type of frame objects such as found in ``tb.tb_frame`` if ``tb`` is a
traceback object.
See :ref:`the language reference <frame-objects>` for details of the
available attributes and operations.
.. data:: GetSetDescriptorType
The type of objects defined in extension modules with ``PyGetSetDef``, such
as ``FrameType.f_locals`` or ``array.array.typecode``. This type is used as
descriptor for object attributes; it has the same purpose as the
:class:`property` type, but for classes defined in extension modules.
.. data:: MemberDescriptorType
The type of objects defined in extension modules with ``PyMemberDef``, such
as ``datetime.timedelta.days``. This type is used as descriptor for simple C
data members which use standard conversion functions; it has the same purpose
as the :class:`property` type, but for classes defined in extension modules.
.. impl-detail::
In other implementations of Python, this type may be identical to
``GetSetDescriptorType``.
.. class:: MappingProxyType(mapping)
Read-only proxy of a mapping. It provides a dynamic view on the mapping's
entries, which means that when the mapping changes, the view reflects these
changes.
.. versionadded:: 3.3
.. versionchanged:: 3.9
Updated to support the new union (``|``) operator from :pep:`584`, which
simply delegates to the underlying mapping.
.. describe:: key in proxy
Return ``True`` if the underlying mapping has a key *key*, else
``False``.
.. describe:: proxy[key]
Return the item of the underlying mapping with key *key*. Raises a
:exc:`KeyError` if *key* is not in the underlying mapping.
.. describe:: iter(proxy)
Return an iterator over the keys of the underlying mapping. This is a
shortcut for ``iter(proxy.keys())``.
.. describe:: len(proxy)
Return the number of items in the underlying mapping.
.. method:: copy()
Return a shallow copy of the underlying mapping.
.. method:: get(key[, default])
Return the value for *key* if *key* is in the underlying mapping, else
*default*. If *default* is not given, it defaults to ``None``, so that
this method never raises a :exc:`KeyError`.
.. method:: items()
Return a new view of the underlying mapping's items (``(key, value)``
pairs).
.. method:: keys()
Return a new view of the underlying mapping's keys.
.. method:: values()
Return a new view of the underlying mapping's values.
.. describe:: reversed(proxy)
Return a reverse iterator over the keys of the underlying mapping.
.. versionadded:: 3.9
Additional Utility Classes and Functions
----------------------------------------
.. class:: SimpleNamespace
A simple :class:`object` subclass that provides attribute access to its
namespace, as well as a meaningful repr.
Unlike :class:`object`, with ``SimpleNamespace`` you can add and remove
attributes. If a ``SimpleNamespace`` object is initialized with keyword
arguments, those are directly added to the underlying namespace.
The type is roughly equivalent to the following code::
class SimpleNamespace:
def __init__(self, /, **kwargs):
self.__dict__.update(kwargs)
def __repr__(self):
items = (f"{k}={v!r}" for k, v in self.__dict__.items())
return "{}({})".format(type(self).__name__, ", ".join(items))
def __eq__(self, other):
if isinstance(self, SimpleNamespace) and isinstance(other, SimpleNamespace):
return self.__dict__ == other.__dict__
return NotImplemented
``SimpleNamespace`` may be useful as a replacement for ``class NS: pass``.
However, for a structured record type use :func:`~collections.namedtuple`
instead.
.. versionadded:: 3.3
.. versionchanged:: 3.9
Attribute order in the repr changed from alphabetical to insertion (like
``dict``).
.. function:: DynamicClassAttribute(fget=None, fset=None, fdel=None, doc=None)
Route attribute access on a class to __getattr__.
This is a descriptor, used to define attributes that act differently when
accessed through an instance and through a class. Instance access remains
normal, but access to an attribute through a class will be routed to the
class's __getattr__ method; this is done by raising AttributeError.
This allows one to have properties active on an instance, and have virtual
attributes on the class with the same name (see :class:`enum.Enum` for an example).
.. versionadded:: 3.4
Coroutine Utility Functions
---------------------------
.. function:: coroutine(gen_func)
This function transforms a :term:`generator` function into a
:term:`coroutine function` which returns a generator-based coroutine.
The generator-based coroutine is still a :term:`generator iterator`,
but is also considered to be a :term:`coroutine` object and is
:term:`awaitable`. However, it may not necessarily implement
the :meth:`__await__` method.
If *gen_func* is a generator function, it will be modified in-place.
If *gen_func* is not a generator function, it will be wrapped. If it
returns an instance of :class:`collections.abc.Generator`, the instance
will be wrapped in an *awaitable* proxy object. All other types
of objects will be returned as is.
.. versionadded:: 3.5
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