cpython/Doc/c-api/module.rst

.. highlight:: c

.. _moduleobjects:

Module Objects
--------------

.. index:: object: module


.. c:var:: PyTypeObject PyModule_Type

   .. index:: single: ModuleType (in module types)

   This instance of :c:type:`PyTypeObject` represents the Python module type.  This
   is exposed to Python programs as ``types.ModuleType``.


.. c:function:: int PyModule_Check(PyObject *p)

   Return true if *p* is a module object, or a subtype of a module object.


.. c:function:: int PyModule_CheckExact(PyObject *p)

   Return true if *p* is a module object, but not a subtype of
   :c:data:`PyModule_Type`.


.. c:function:: PyObject* PyModule_NewObject(PyObject *name)

   .. index::
      single: __name__ (module attribute)
      single: __doc__ (module attribute)
      single: __file__ (module attribute)
      single: __package__ (module attribute)
      single: __loader__ (module attribute)

   Return a new module object with the :attr:`__name__` attribute set to *name*.
   The module's :attr:`__name__`, :attr:`__doc__`, :attr:`__package__`, and
   :attr:`__loader__` attributes are filled in (all but :attr:`__name__` are set
   to ``None``); the caller is responsible for providing a :attr:`__file__`
   attribute.

   .. versionadded:: 3.3

   .. versionchanged:: 3.4
      :attr:`__package__` and :attr:`__loader__` are set to ``None``.


.. c:function:: PyObject* PyModule_New(const char *name)

   Similar to :c:func:`PyModule_NewObject`, but the name is a UTF-8 encoded
   string instead of a Unicode object.


.. c:function:: PyObject* PyModule_GetDict(PyObject *module)

   .. index:: single: __dict__ (module attribute)

   Return the dictionary object that implements *module*'s namespace; this object
   is the same as the :attr:`~object.__dict__` attribute of the module object.
   If *module* is not a module object (or a subtype of a module object),
   :exc:`SystemError` is raised and ``NULL`` is returned.

   It is recommended extensions use other :c:func:`PyModule_\*` and
   :c:func:`PyObject_\*` functions rather than directly manipulate a module's
   :attr:`~object.__dict__`.


.. c:function:: PyObject* PyModule_GetNameObject(PyObject *module)

   .. index::
      single: __name__ (module attribute)
      single: SystemError (built-in exception)

   Return *module*'s :attr:`__name__` value.  If the module does not provide one,
   or if it is not a string, :exc:`SystemError` is raised and ``NULL`` is returned.

   .. versionadded:: 3.3


.. c:function:: const char* PyModule_GetName(PyObject *module)

   Similar to :c:func:`PyModule_GetNameObject` but return the name encoded to
   ``'utf-8'``.

.. c:function:: void* PyModule_GetState(PyObject *module)

   Return the "state" of the module, that is, a pointer to the block of memory
   allocated at module creation time, or ``NULL``.  See
   :c:member:`PyModuleDef.m_size`.


.. c:function:: PyModuleDef* PyModule_GetDef(PyObject *module)

   Return a pointer to the :c:type:`PyModuleDef` struct from which the module was
   created, or ``NULL`` if the module wasn't created from a definition.


.. c:function:: PyObject* PyModule_GetFilenameObject(PyObject *module)

   .. index::
      single: __file__ (module attribute)
      single: SystemError (built-in exception)

   Return the name of the file from which *module* was loaded using *module*'s
   :attr:`__file__` attribute.  If this is not defined, or if it is not a
   unicode string, raise :exc:`SystemError` and return ``NULL``; otherwise return
   a reference to a Unicode object.

   .. versionadded:: 3.2


.. c:function:: const char* PyModule_GetFilename(PyObject *module)

   Similar to :c:func:`PyModule_GetFilenameObject` but return the filename
   encoded to 'utf-8'.

   .. deprecated:: 3.2
      :c:func:`PyModule_GetFilename` raises :c:type:`UnicodeEncodeError` on
      unencodable filenames, use :c:func:`PyModule_GetFilenameObject` instead.


.. _initializing-modules:

Initializing C modules
^^^^^^^^^^^^^^^^^^^^^^

Modules objects are usually created from extension modules (shared libraries
which export an initialization function), or compiled-in modules
(where the initialization function is added using :c:func:`PyImport_AppendInittab`).
See :ref:`building` or :ref:`extending-with-embedding` for details.

The initialization function can either pass a module definition instance
to :c:func:`PyModule_Create`, and return the resulting module object,
or request "multi-phase initialization" by returning the definition struct itself.

.. c:type:: PyModuleDef

   The module definition struct, which holds all information needed to create
   a module object. There is usually only one statically initialized variable
   of this type for each module.

   .. c:member:: PyModuleDef_Base m_base

      Always initialize this member to :const:`PyModuleDef_HEAD_INIT`.

   .. c:member:: const char *m_name

      Name for the new module.

   .. c:member:: const char *m_doc

      Docstring for the module; usually a docstring variable created with
      :c:func:`PyDoc_STRVAR` is used.

   .. c:member:: Py_ssize_t m_size

      Module state may be kept in a per-module memory area that can be
      retrieved with :c:func:`PyModule_GetState`, rather than in static globals.
      This makes modules safe for use in multiple sub-interpreters.

      This memory area is allocated based on *m_size* on module creation,
      and freed when the module object is deallocated, after the
      :c:member:`m_free` function has been called, if present.

      Setting ``m_size`` to ``-1`` means that the module does not support
      sub-interpreters, because it has global state.

      Setting it to a non-negative value means that the module can be
      re-initialized and specifies the additional amount of memory it requires
      for its state. Non-negative ``m_size`` is required for multi-phase
      initialization.

      See :PEP:`3121` for more details.

   .. c:member:: PyMethodDef* m_methods

      A pointer to a table of module-level functions, described by
      :c:type:`PyMethodDef` values.  Can be ``NULL`` if no functions are present.

   .. c:member:: PyModuleDef_Slot* m_slots

      An array of slot definitions for multi-phase initialization, terminated by
      a ``{0, NULL}`` entry.
      When using single-phase initialization, *m_slots* must be ``NULL``.

      .. versionchanged:: 3.5

         Prior to version 3.5, this member was always set to ``NULL``,
         and was defined as:

           .. c:member:: inquiry m_reload

   .. c:member:: traverseproc m_traverse

      A traversal function to call during GC traversal of the module object, or
      ``NULL`` if not needed. This function may be called before module state
      is allocated (:c:func:`PyModule_GetState()` may return `NULL`),
      and before the :c:member:`Py_mod_exec` function is executed.

   .. c:member:: inquiry m_clear

      A clear function to call during GC clearing of the module object, or
      ``NULL`` if not needed. This function may be called before module state
      is allocated (:c:func:`PyModule_GetState()` may return `NULL`),
      and before the :c:member:`Py_mod_exec` function is executed.

   .. c:member:: freefunc m_free

      A function to call during deallocation of the module object, or ``NULL`` if
      not needed. This function may be called before module state
      is allocated (:c:func:`PyModule_GetState()` may return `NULL`),
      and before the :c:member:`Py_mod_exec` function is executed.

Single-phase initialization
...........................

The module initialization function may create and return the module object
directly. This is referred to as "single-phase initialization", and uses one
of the following two module creation functions:

.. c:function:: PyObject* PyModule_Create(PyModuleDef *def)

   Create a new module object, given the definition in *def*.  This behaves
   like :c:func:`PyModule_Create2` with *module_api_version* set to
   :const:`PYTHON_API_VERSION`.


.. c:function:: PyObject* PyModule_Create2(PyModuleDef *def, int module_api_version)

   Create a new module object, given the definition in *def*, assuming the
   API version *module_api_version*.  If that version does not match the version
   of the running interpreter, a :exc:`RuntimeWarning` is emitted.

   .. note::

      Most uses of this function should be using :c:func:`PyModule_Create`
      instead; only use this if you are sure you need it.

Before it is returned from in the initialization function, the resulting module
object is typically populated using functions like :c:func:`PyModule_AddObject`.

.. _multi-phase-initialization:

Multi-phase initialization
..........................

An alternate way to specify extensions is to request "multi-phase initialization".
Extension modules created this way behave more like Python modules: the
initialization is split between the *creation phase*, when the module object
is created, and the *execution phase*, when it is populated.
The distinction is similar to the :py:meth:`__new__` and :py:meth:`__init__` methods
of classes.

Unlike modules created using single-phase initialization, these modules are not
singletons: if the *sys.modules* entry is removed and the module is re-imported,
a new module object is created, and the old module is subject to normal garbage
collection -- as with Python modules.
By default, multiple modules created from the same definition should be
independent: changes to one should not affect the others.
This means that all state should be specific to the module object (using e.g.
using :c:func:`PyModule_GetState`), or its contents (such as the module's
:attr:`__dict__` or individual classes created with :c:func:`PyType_FromSpec`).

All modules created using multi-phase initialization are expected to support
:ref:`sub-interpreters <sub-interpreter-support>`. Making sure multiple modules
are independent is typically enough to achieve this.

To request multi-phase initialization, the initialization function
(PyInit_modulename) returns a :c:type:`PyModuleDef` instance with non-empty
:c:member:`~PyModuleDef.m_slots`. Before it is returned, the ``PyModuleDef``
instance must be initialized with the following function:

.. c:function:: PyObject* PyModuleDef_Init(PyModuleDef *def)

   Ensures a module definition is a properly initialized Python object that
   correctly reports its type and reference count.

   Returns *def* cast to ``PyObject*``, or ``NULL`` if an error occurred.

   .. versionadded:: 3.5

The *m_slots* member of the module definition must point to an array of
``PyModuleDef_Slot`` structures:

.. c:type:: PyModuleDef_Slot

   .. c:member:: int slot

      A slot ID, chosen from the available values explained below.

   .. c:member:: void* value

      Value of the slot, whose meaning depends on the slot ID.

   .. versionadded:: 3.5

The *m_slots* array must be terminated by a slot with id 0.

The available slot types are:

.. c:var:: Py_mod_create

   Specifies a function that is called to create the module object itself.
   The *value* pointer of this slot must point to a function of the signature:

   .. c:function:: PyObject* create_module(PyObject *spec, PyModuleDef *def)

   The function receives a :py:class:`~importlib.machinery.ModuleSpec`
   instance, as defined in :PEP:`451`, and the module definition.
   It should return a new module object, or set an error
   and return ``NULL``.

   This function should be kept minimal. In particular, it should not
   call arbitrary Python code, as trying to import the same module again may
   result in an infinite loop.

   Multiple ``Py_mod_create`` slots may not be specified in one module
   definition.

   If ``Py_mod_create`` is not specified, the import machinery will create
   a normal module object using :c:func:`PyModule_New`. The name is taken from
   *spec*, not the definition, to allow extension modules to dynamically adjust
   to their place in the module hierarchy and be imported under different
   names through symlinks, all while sharing a single module definition.

   There is no requirement for the returned object to be an instance of
   :c:type:`PyModule_Type`. Any type can be used, as long as it supports
   setting and getting import-related attributes.
   However, only ``PyModule_Type`` instances may be returned if the
   ``PyModuleDef`` has non-``NULL`` ``m_traverse``, ``m_clear``,
   ``m_free``; non-zero ``m_size``; or slots other than ``Py_mod_create``.

.. c:var:: Py_mod_exec

   Specifies a function that is called to *execute* the module.
   This is equivalent to executing the code of a Python module: typically,
   this function adds classes and constants to the module.
   The signature of the function is:

   .. c:function:: int exec_module(PyObject* module)

   If multiple ``Py_mod_exec`` slots are specified, they are processed in the
   order they appear in the *m_slots* array.

See :PEP:`489` for more details on multi-phase initialization.

Low-level module creation functions
...................................

The following functions are called under the hood when using multi-phase
initialization. They can be used directly, for example when creating module
objects dynamically. Note that both ``PyModule_FromDefAndSpec`` and
``PyModule_ExecDef`` must be called to fully initialize a module.

.. c:function:: PyObject * PyModule_FromDefAndSpec(PyModuleDef *def, PyObject *spec)

   Create a new module object, given the definition in *module* and the
   ModuleSpec *spec*.  This behaves like :c:func:`PyModule_FromDefAndSpec2`
   with *module_api_version* set to :const:`PYTHON_API_VERSION`.

   .. versionadded:: 3.5

.. c:function:: PyObject * PyModule_FromDefAndSpec2(PyModuleDef *def, PyObject *spec, int module_api_version)

   Create a new module object, given the definition in *module* and the
   ModuleSpec *spec*, assuming the API version *module_api_version*.
   If that version does not match the version of the running interpreter,
   a :exc:`RuntimeWarning` is emitted.

   .. note::

      Most uses of this function should be using :c:func:`PyModule_FromDefAndSpec`
      instead; only use this if you are sure you need it.

   .. versionadded:: 3.5

.. c:function:: int PyModule_ExecDef(PyObject *module, PyModuleDef *def)

   Process any execution slots (:c:data:`Py_mod_exec`) given in *def*.

   .. versionadded:: 3.5

.. c:function:: int PyModule_SetDocString(PyObject *module, const char *docstring)

   Set the docstring for *module* to *docstring*.
   This function is called automatically when creating a module from
   ``PyModuleDef``, using either ``PyModule_Create`` or
   ``PyModule_FromDefAndSpec``.

   .. versionadded:: 3.5

.. c:function:: int PyModule_AddFunctions(PyObject *module, PyMethodDef *functions)

   Add the functions from the ``NULL`` terminated *functions* array to *module*.
   Refer to the :c:type:`PyMethodDef` documentation for details on individual
   entries (due to the lack of a shared module namespace, module level
   "functions" implemented in C typically receive the module as their first
   parameter, making them similar to instance methods on Python classes).
   This function is called automatically when creating a module from
   ``PyModuleDef``, using either ``PyModule_Create`` or
   ``PyModule_FromDefAndSpec``.

   .. versionadded:: 3.5

Support functions
.................

The module initialization function (if using single phase initialization) or
a function called from a module execution slot (if using multi-phase
initialization), can use the following functions to help initialize the module
state:

.. c:function:: int PyModule_AddObject(PyObject *module, const char *name, PyObject *value)

   Add an object to *module* as *name*.  This is a convenience function which can
   be used from the module's initialization function.  This steals a reference to
   *value* on success.  Return ``-1`` on error, ``0`` on success.

   .. note::

      Unlike other functions that steal references, ``PyModule_AddObject()`` only
      decrements the reference count of *value* **on success**.

      This means that its return value must be checked, and calling code must
      :c:func:`Py_DECREF` *value* manually on error. Example usage::

         Py_INCREF(spam);
         if (PyModule_AddObject(module, "spam", spam) < 0) {
             Py_DECREF(module);
             Py_DECREF(spam);
             return NULL;
         }

.. c:function:: int PyModule_AddIntConstant(PyObject *module, const char *name, long value)

   Add an integer constant to *module* as *name*.  This convenience function can be
   used from the module's initialization function. Return ``-1`` on error, ``0`` on
   success.


.. c:function:: int PyModule_AddStringConstant(PyObject *module, const char *name, const char *value)

   Add a string constant to *module* as *name*.  This convenience function can be
   used from the module's initialization function.  The string *value* must be
   ``NULL``-terminated.  Return ``-1`` on error, ``0`` on success.


.. c:function:: int PyModule_AddIntMacro(PyObject *module, macro)

   Add an int constant to *module*. The name and the value are taken from
   *macro*. For example ``PyModule_AddIntMacro(module, AF_INET)`` adds the int
   constant *AF_INET* with the value of *AF_INET* to *module*.
   Return ``-1`` on error, ``0`` on success.


.. c:function:: int PyModule_AddStringMacro(PyObject *module, macro)

   Add a string constant to *module*.


Module lookup
^^^^^^^^^^^^^

Single-phase initialization creates singleton modules that can be looked up
in the context of the current interpreter. This allows the module object to be
retrieved later with only a reference to the module definition.

These functions will not work on modules created using multi-phase initialization,
since multiple such modules can be created from a single definition.

.. c:function:: PyObject* PyState_FindModule(PyModuleDef *def)

   Returns the module object that was created from *def* for the current interpreter.
   This method requires that the module object has been attached to the interpreter state with
   :c:func:`PyState_AddModule` beforehand. In case the corresponding module object is not
   found or has not been attached to the interpreter state yet, it returns ``NULL``.

.. c:function:: int PyState_AddModule(PyObject *module, PyModuleDef *def)

   Attaches the module object passed to the function to the interpreter state. This allows
   the module object to be accessible via :c:func:`PyState_FindModule`.

   Only effective on modules created using single-phase initialization.

   Python calls ``PyState_AddModule`` automatically after importing a module,
   so it is unnecessary (but harmless) to call it from module initialization
   code. An explicit call is needed only if the module's own init code
   subsequently calls ``PyState_FindModule``.
   The function is mainly intended for implementing alternative import
   mechanisms (either by calling it directly, or by referring to its
   implementation for details of the required state updates).

   Return 0 on success or -1 on failure.

   .. versionadded:: 3.3

.. c:function:: int PyState_RemoveModule(PyModuleDef *def)

   Removes the module object created from *def* from the interpreter state.
   Return 0 on success or -1 on failure.

   .. versionadded:: 3.3