.. highlight:: c
.. _importing:
Importing Modules
=================
.. c:function:: PyObject* PyImport_ImportModule(const char *name)
.. index::
single: package variable; __all__
single: __all__ (package variable)
single: modules (in module sys)
This is a simplified interface to :c:func:`PyImport_ImportModuleEx` below,
leaving the *globals* and *locals* arguments set to ``NULL`` and *level* set
to 0. When the *name*
argument contains a dot (when it specifies a submodule of a package), the
*fromlist* argument is set to the list ``['*']`` so that the return value is the
named module rather than the top-level package containing it as would otherwise
be the case. (Unfortunately, this has an additional side effect when *name* in
fact specifies a subpackage instead of a submodule: the submodules specified in
the package's ``__all__`` variable are loaded.) Return a new reference to the
imported module, or ``NULL`` with an exception set on failure. A failing
import of a module doesn't leave the module in :data:`sys.modules`.
This function always uses absolute imports.
.. c:function:: PyObject* PyImport_ImportModuleNoBlock(const char *name)
This function is a deprecated alias of :c:func:`PyImport_ImportModule`.
.. versionchanged:: 3.3
This function used to fail immediately when the import lock was held
by another thread. In Python 3.3 though, the locking scheme switched
to per-module locks for most purposes, so this function's special
behaviour isn't needed anymore.
.. c:function:: PyObject* PyImport_ImportModuleEx(const char *name, PyObject *globals, PyObject *locals, PyObject *fromlist)
.. index:: builtin: __import__
Import a module. This is best described by referring to the built-in Python
function :func:`__import__`.
The return value is a new reference to the imported module or top-level
package, or ``NULL`` with an exception set on failure. Like for
:func:`__import__`, the return value when a submodule of a package was
requested is normally the top-level package, unless a non-empty *fromlist*
was given.
Failing imports remove incomplete module objects, like with
:c:func:`PyImport_ImportModule`.
.. c:function:: PyObject* PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals, PyObject *locals, PyObject *fromlist, int level)
Import a module. This is best described by referring to the built-in Python
function :func:`__import__`, as the standard :func:`__import__` function calls
this function directly.
The return value is a new reference to the imported module or top-level package,
or ``NULL`` with an exception set on failure. Like for :func:`__import__`,
the return value when a submodule of a package was requested is normally the
top-level package, unless a non-empty *fromlist* was given.
.. versionadded:: 3.3
.. c:function:: PyObject* PyImport_ImportModuleLevel(const char *name, PyObject *globals, PyObject *locals, PyObject *fromlist, int level)
Similar to :c:func:`PyImport_ImportModuleLevelObject`, but the name is a
UTF-8 encoded string instead of a Unicode object.
.. versionchanged:: 3.3
Negative values for *level* are no longer accepted.
.. c:function:: PyObject* PyImport_Import(PyObject *name)
This is a higher-level interface that calls the current "import hook
function" (with an explicit *level* of 0, meaning absolute import). It
invokes the :func:`__import__` function from the ``__builtins__`` of the
current globals. This means that the import is done using whatever import
hooks are installed in the current environment.
This function always uses absolute imports.
.. c:function:: PyObject* PyImport_ReloadModule(PyObject *m)
Reload a module. Return a new reference to the reloaded module, or ``NULL`` with
an exception set on failure (the module still exists in this case).
.. c:function:: PyObject* PyImport_AddModuleObject(PyObject *name)
Return the module object corresponding to a module name. The *name* argument
may be of the form ``package.module``. First check the modules dictionary if
there's one there, and if not, create a new one and insert it in the modules
dictionary. Return ``NULL`` with an exception set on failure.
.. note::
This function does not load or import the module; if the module wasn't already
loaded, you will get an empty module object. Use :c:func:`PyImport_ImportModule`
or one of its variants to import a module. Package structures implied by a
dotted name for *name* are not created if not already present.
.. versionadded:: 3.3
.. c:function:: PyObject* PyImport_AddModule(const char *name)
Similar to :c:func:`PyImport_AddModuleObject`, but the name is a UTF-8
encoded string instead of a Unicode object.
.. c:function:: PyObject* PyImport_ExecCodeModule(const char *name, PyObject *co)
.. index:: builtin: compile
Given a module name (possibly of the form ``package.module``) and a code object
read from a Python bytecode file or obtained from the built-in function
:func:`compile`, load the module. Return a new reference to the module object,
or ``NULL`` with an exception set if an error occurred. *name*
is removed from :attr:`sys.modules` in error cases, even if *name* was already
in :attr:`sys.modules` on entry to :c:func:`PyImport_ExecCodeModule`. Leaving
incompletely initialized modules in :attr:`sys.modules` is dangerous, as imports of
such modules have no way to know that the module object is an unknown (and
probably damaged with respect to the module author's intents) state.
The module's :attr:`__spec__` and :attr:`__loader__` will be set, if
not set already, with the appropriate values. The spec's loader will
be set to the module's ``__loader__`` (if set) and to an instance of
:class:`SourceFileLoader` otherwise.
The module's :attr:`__file__` attribute will be set to the code object's
:c:member:`co_filename`. If applicable, :attr:`__cached__` will also
be set.
This function will reload the module if it was already imported. See
:c:func:`PyImport_ReloadModule` for the intended way to reload a module.
If *name* points to a dotted name of the form ``package.module``, any package
structures not already created will still not be created.
See also :c:func:`PyImport_ExecCodeModuleEx` and
:c:func:`PyImport_ExecCodeModuleWithPathnames`.
.. c:function:: PyObject* PyImport_ExecCodeModuleEx(const char *name, PyObject *co, const char *pathname)
Like :c:func:`PyImport_ExecCodeModule`, but the :attr:`__file__` attribute of
the module object is set to *pathname* if it is non-``NULL``.
See also :c:func:`PyImport_ExecCodeModuleWithPathnames`.
.. c:function:: PyObject* PyImport_ExecCodeModuleObject(PyObject *name, PyObject *co, PyObject *pathname, PyObject *cpathname)
Like :c:func:`PyImport_ExecCodeModuleEx`, but the :attr:`__cached__`
attribute of the module object is set to *cpathname* if it is
non-``NULL``. Of the three functions, this is the preferred one to use.
.. versionadded:: 3.3
.. c:function:: PyObject* PyImport_ExecCodeModuleWithPathnames(const char *name, PyObject *co, const char *pathname, const char *cpathname)
Like :c:func:`PyImport_ExecCodeModuleObject`, but *name*, *pathname* and
*cpathname* are UTF-8 encoded strings. Attempts are also made to figure out
what the value for *pathname* should be from *cpathname* if the former is
set to ``NULL``.
.. versionadded:: 3.2
.. versionchanged:: 3.3
Uses :func:`imp.source_from_cache()` in calculating the source path if
only the bytecode path is provided.
.. c:function:: long PyImport_GetMagicNumber()
Return the magic number for Python bytecode files (a.k.a. :file:`.pyc` file).
The magic number should be present in the first four bytes of the bytecode
file, in little-endian byte order. Returns ``-1`` on error.
.. versionchanged:: 3.3
Return value of ``-1`` upon failure.
.. c:function:: const char * PyImport_GetMagicTag()
Return the magic tag string for :pep:`3147` format Python bytecode file
names. Keep in mind that the value at ``sys.implementation.cache_tag`` is
authoritative and should be used instead of this function.
.. versionadded:: 3.2
.. c:function:: PyObject* PyImport_GetModuleDict()
Return the dictionary used for the module administration (a.k.a.
``sys.modules``). Note that this is a per-interpreter variable.
.. c:function:: PyObject* PyImport_GetModule(PyObject *name)
Return the already imported module with the given name. If the
module has not been imported yet then returns ``NULL`` but does not set
an error. Returns ``NULL`` and sets an error if the lookup failed.
.. versionadded:: 3.7
.. c:function:: PyObject* PyImport_GetImporter(PyObject *path)
Return a finder object for a :data:`sys.path`/:attr:`pkg.__path__` item
*path*, possibly by fetching it from the :data:`sys.path_importer_cache`
dict. If it wasn't yet cached, traverse :data:`sys.path_hooks` until a hook
is found that can handle the path item. Return ``None`` if no hook could;
this tells our caller that the :term:`path based finder` could not find a
finder for this path item. Cache the result in :data:`sys.path_importer_cache`.
Return a new reference to the finder object.
.. c:function:: int PyImport_ImportFrozenModuleObject(PyObject *name)
Load a frozen module named *name*. Return ``1`` for success, ``0`` if the
module is not found, and ``-1`` with an exception set if the initialization
failed. To access the imported module on a successful load, use
:c:func:`PyImport_ImportModule`. (Note the misnomer --- this function would
reload the module if it was already imported.)
.. versionadded:: 3.3
.. versionchanged:: 3.4
The ``__file__`` attribute is no longer set on the module.
.. c:function:: int PyImport_ImportFrozenModule(const char *name)
Similar to :c:func:`PyImport_ImportFrozenModuleObject`, but the name is a
UTF-8 encoded string instead of a Unicode object.
.. c:struct:: _frozen
.. index:: single: freeze utility
This is the structure type definition for frozen module descriptors, as
generated by the :program:`freeze` utility (see :file:`Tools/freeze/` in the
Python source distribution). Its definition, found in :file:`Include/import.h`,
is::
struct _frozen {
const char *name;
const unsigned char *code;
int size;
bool is_package;
};
.. versionchanged:: 3.11
The new ``is_package`` field indicates whether the module is a package or not.
This replaces setting the ``size`` field to a negative value.
.. c:var:: const struct _frozen* PyImport_FrozenModules
This pointer is initialized to point to an array of :c:struct:`_frozen`
records, terminated by one whose members are all ``NULL`` or zero. When a frozen
module is imported, it is searched in this table. Third-party code could play
tricks with this to provide a dynamically created collection of frozen modules.
.. c:function:: int PyImport_AppendInittab(const char *name, PyObject* (*initfunc)(void))
Add a single module to the existing table of built-in modules. This is a
convenience wrapper around :c:func:`PyImport_ExtendInittab`, returning ``-1`` if
the table could not be extended. The new module can be imported by the name
*name*, and uses the function *initfunc* as the initialization function called
on the first attempted import. This should be called before
:c:func:`Py_Initialize`.
.. c:struct:: _inittab
Structure describing a single entry in the list of built-in modules. Each of
these structures gives the name and initialization function for a module built
into the interpreter. The name is an ASCII encoded string. Programs which
embed Python may use an array of these structures in conjunction with
:c:func:`PyImport_ExtendInittab` to provide additional built-in modules.
The structure is defined in :file:`Include/import.h` as::
struct _inittab {
const char *name; /* ASCII encoded string */
PyObject* (*initfunc)(void);
};
.. c:function:: int PyImport_ExtendInittab(struct _inittab *newtab)
Add a collection of modules to the table of built-in modules. The *newtab*
array must end with a sentinel entry which contains ``NULL`` for the :attr:`name`
field; failure to provide the sentinel value can result in a memory fault.
Returns ``0`` on success or ``-1`` if insufficient memory could be allocated to
extend the internal table. In the event of failure, no modules are added to the
internal table. This must be called before :c:func:`Py_Initialize`.
If Python is initialized multiple times, :c:func:`PyImport_AppendInittab` or
:c:func:`PyImport_ExtendInittab` must be called before each Python
initialization.
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