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v3.14.7
Doc/c-api/module.rst
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Petr Viktorin
[3.14] gh-144473: Add "steal" term to glossary; clarify "stealing" on error (GH-144502) (GH-152772)
01 июл 2026, 15:25
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01 июл 2026, 15:25
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.. highlight:: c .. _moduleobjects: Module Objects -------------- .. index:: pair: 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 :py:class:`types.ModuleType`. .. c:function:: int PyModule_Check(PyObject *p) Return true if *p* is a module object, or a subtype of a module object. This function always succeeds. .. c:function:: int PyModule_CheckExact(PyObject *p) Return true if *p* is a module object, but not a subtype of :c:data:`PyModule_Type`. This function always succeeds. .. 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 :attr:`module.__name__` set to *name*. The module's :attr:`!__name__`, :attr:`~module.__doc__`, :attr:`~module.__package__` and :attr:`~module.__loader__` attributes are filled in (all but :attr:`!__name__` are set to ``None``). The caller is responsible for setting a :attr:`~module.__file__` attribute. Return ``NULL`` with an exception set on error. .. versionadded:: 3.3 .. versionchanged:: 3.4 :attr:`~module.__package__` and :attr:`~module.__loader__` are now 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 ``PyModule_*`` and ``PyObject_*`` functions rather than directly manipulate a module's :attr:`~object.__dict__`. The returned reference is borrowed from the module; it is valid until the module is destroyed. .. c:function:: PyObject* PyModule_GetNameObject(PyObject *module) .. index:: single: __name__ (module attribute) single: SystemError (built-in exception) Return *module*'s :attr:`~module.__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'``. The returned buffer is only valid until the module is renamed or destroyed. Note that Python code may rename a module by setting its :py:attr:`~module.__name__` attribute. .. 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. On error, return ``NULL`` with an exception set. Use :c:func:`PyErr_Occurred` to tell this case apart from a missing :c:type:`!PyModuleDef`. .. 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:`~module.__file__` attribute. If this is not defined, or if it is not a 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'. The returned buffer is only valid until the module's :py:attr:`~module.__file__` attribute is reassigned or the module is destroyed. .. deprecated:: 3.2 :c:func:`PyModule_GetFilename` raises :exc:`UnicodeEncodeError` on unencodable filenames, use :c:func:`PyModule_GetFilenameObject` instead. .. _pymoduledef: Module definitions ------------------ The functions in the previous section work on any module object, including modules imported from Python code. Modules defined using the C API typically use a *module definition*, :c:type:`PyModuleDef` -- a statically allocated, constant “description" of how a module should be created. The definition is usually used to define an extension's “main” module object (see :ref:`extension-modules` for details). It is also used to :ref:`create extension modules dynamically <moduledef-dynamic>`. Unlike :c:func:`PyModule_New`, the definition allows management of *module state* -- a piece of memory that is allocated and cleared together with the module object. Unlike the module's Python attributes, Python code cannot replace or delete data stored in module state. .. c:type:: PyModuleDef The module definition struct, which holds all information needed to create a module object. This structure must be statically allocated (or be otherwise guaranteed to be valid while any modules created from it exist). Usually, there is only one variable of this type for each extension module. .. c:member:: PyModuleDef_Base m_base Always initialize this member to :c:macro:`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:macro:`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:`~PyModuleDef.m_free` function has been called, if present. 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. Setting ``m_size`` to ``-1`` means that the module does not support sub-interpreters, because it has global state. Negative ``m_size`` is only allowed when using :ref:`legacy single-phase initialization <single-phase-initialization>` or when :ref:`creating modules dynamically <moduledef-dynamic>`. 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 legacy 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 is not 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, this function is 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``. .. versionchanged:: 3.9 No longer called before the module state is allocated. .. c:member:: inquiry m_clear A clear function to call during GC clearing of the module object, or ``NULL`` if not needed. This function is not 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, this function is 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``. Like :c:member:`PyTypeObject.tp_clear`, this function is not *always* called before a module is deallocated. For example, when reference counting is enough to determine that an object is no longer used, the cyclic garbage collector is not involved and :c:member:`~PyModuleDef.m_free` is called directly. .. versionchanged:: 3.9 No longer called before the module state is allocated. .. c:member:: freefunc m_free A function to call during deallocation of the module object, or ``NULL`` if not needed. This function is not 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, this function is 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``. .. versionchanged:: 3.9 No longer called before the module state is allocated. .. c:var:: PyTypeObject PyModuleDef_Type The type of ``PyModuleDef`` objects. Module slots ............ .. 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 available slot types are: .. c:macro:: 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) :no-index-entry: :no-contents-entry: 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``. .. versionadded:: 3.5 .. c:macro:: 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) :no-index-entry: :no-contents-entry: If multiple ``Py_mod_exec`` slots are specified, they are processed in the order they appear in the *m_slots* array. .. versionadded:: 3.5 .. c:macro:: Py_mod_multiple_interpreters Specifies one of the following values: .. c:namespace:: NULL .. c:macro:: Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED The module does not support being imported in subinterpreters. .. c:macro:: Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED The module supports being imported in subinterpreters, but only when they share the main interpreter's GIL. (See :ref:`isolating-extensions-howto`.) .. c:macro:: Py_MOD_PER_INTERPRETER_GIL_SUPPORTED The module supports being imported in subinterpreters, even when they have their own GIL. (See :ref:`isolating-extensions-howto`.) This slot determines whether or not importing this module in a subinterpreter will fail. Multiple ``Py_mod_multiple_interpreters`` slots may not be specified in one module definition. If ``Py_mod_multiple_interpreters`` is not specified, the import machinery defaults to ``Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED``. .. versionadded:: 3.12 .. c:macro:: Py_mod_gil Specifies one of the following values: .. c:namespace:: NULL .. c:macro:: Py_MOD_GIL_USED The module depends on the presence of the global interpreter lock (GIL), and may access global state without synchronization. .. c:macro:: Py_MOD_GIL_NOT_USED The module is safe to run without an active GIL. This slot is ignored by Python builds not configured with :option:`--disable-gil`. Otherwise, it determines whether or not importing this module will cause the GIL to be automatically enabled. See :ref:`whatsnew313-free-threaded-cpython` for more detail. Multiple ``Py_mod_gil`` slots may not be specified in one module definition. If ``Py_mod_gil`` is not specified, the import machinery defaults to ``Py_MOD_GIL_USED``. .. versionadded:: 3.13 .. _moduledef-dynamic: Creating extension modules dynamically -------------------------------------- The following functions may be used to create a module outside of an extension's :ref:`initialization function <extension-export-hook>`. They are also used in :ref:`single-phase initialization <single-phase-initialization>`. .. c:function:: PyObject* PyModule_Create(PyModuleDef *def) Create a new module object, given the definition in *def*. This is a macro that calls :c:func:`PyModule_Create2` with *module_api_version* set to :c:macro:`PYTHON_API_VERSION`, or to :c:macro:`PYTHON_ABI_VERSION` if using the :ref:`limited API <limited-c-api>`. .. 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. Return ``NULL`` with an exception set on error. This function does not support slots. The :c:member:`~PyModuleDef.m_slots` member of *def* must be ``NULL``. .. note:: Most uses of this function should be using :c:func:`PyModule_Create` instead; only use this if you are sure you need it. .. c:function:: PyObject * PyModule_FromDefAndSpec(PyModuleDef *def, PyObject *spec) This macro calls :c:func:`PyModule_FromDefAndSpec2` with *module_api_version* set to :c:macro:`PYTHON_API_VERSION`, or to :c:macro:`PYTHON_ABI_VERSION` if using the :ref:`limited API <limited-c-api>`. .. 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 *def* 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. Return ``NULL`` with an exception set on error. Note that this does not process execution slots (:c:data:`Py_mod_exec`). Both ``PyModule_FromDefAndSpec`` and ``PyModule_ExecDef`` must be called to fully initialize a module. .. 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:macro:: PYTHON_API_VERSION The C API version. Defined for backwards compatibility. Currently, this constant is not updated in new Python versions, and is not useful for versioning. This may change in the future. .. c:macro:: PYTHON_ABI_VERSION Defined as ``3`` for backwards compatibility. Currently, this constant is not updated in new Python versions, and is not useful for versioning. This may change in the future. Support functions ----------------- The following functions are provided to help initialize a module state. They are intended for a module's execution slots (:c:data:`Py_mod_exec`), the initialization function for legacy :ref:`single-phase initialization <single-phase-initialization>`, or code that creates modules dynamically. .. c:function:: int PyModule_AddObjectRef(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. On success, return ``0``. On error, raise an exception and return ``-1``. Example usage:: static int add_spam(PyObject *module, int value) { PyObject *obj = PyLong_FromLong(value); if (obj == NULL) { return -1; } int res = PyModule_AddObjectRef(module, "spam", obj); Py_DECREF(obj); return res; } To be convenient, the function accepts ``NULL`` *value* with an exception set. In this case, return ``-1`` and just leave the raised exception unchanged. The example can also be written without checking explicitly if *obj* is ``NULL``:: static int add_spam(PyObject *module, int value) { PyObject *obj = PyLong_FromLong(value); int res = PyModule_AddObjectRef(module, "spam", obj); Py_XDECREF(obj); return res; } Note that ``Py_XDECREF()`` should be used instead of ``Py_DECREF()`` in this case, since *obj* can be ``NULL``. The number of different *name* strings passed to this function should be kept small, usually by only using statically allocated strings as *name*. For names that aren't known at compile time, prefer calling :c:func:`PyUnicode_FromString` and :c:func:`PyObject_SetAttr` directly. For more details, see :c:func:`PyUnicode_InternFromString`, which may be used internally to create a key object. .. versionadded:: 3.10 .. c:function:: int PyModule_Add(PyObject *module, const char *name, PyObject *value) Similar to :c:func:`PyModule_AddObjectRef`, but ":term:`steals <steal>`" a reference to *value* (even on error). It can be called with a result of function that returns a new reference without bothering to check its result or even saving it to a variable. Example usage:: if (PyModule_Add(module, "spam", PyBytes_FromString(value)) < 0) { goto error; } .. versionadded:: 3.13 .. c:function:: int PyModule_AddObject(PyObject *module, const char *name, PyObject *value) Similar to :c:func:`PyModule_AddObjectRef`, but :term:`steals <steal>` a reference to *value* on success (if it returns ``0``). The new :c:func:`PyModule_Add` or :c:func:`PyModule_AddObjectRef` functions are recommended, since it is easy to introduce reference leaks by misusing the :c:func:`PyModule_AddObject` function. .. note:: Unlike other functions that steal references, ``PyModule_AddObject()`` only releases the reference to *value* **on success**. This means that its return value must be checked, and calling code must :c:func:`Py_XDECREF` *value* manually on error. Example usage:: PyObject *obj = PyBytes_FromString(value); if (PyModule_AddObject(module, "spam", obj) < 0) { // If 'obj' is not NULL and PyModule_AddObject() failed, // 'obj' strong reference must be deleted with Py_XDECREF(). // If 'obj' is NULL, Py_XDECREF() does nothing. Py_XDECREF(obj); goto error; } // PyModule_AddObject() stole a reference to obj: // Py_XDECREF(obj) is not needed here. .. soft-deprecated:: 3.13 .. 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`` with an exception set on error, ``0`` on success. This is a convenience function that calls :c:func:`PyLong_FromLong` and :c:func:`PyModule_AddObjectRef`; see their documentation for details. .. 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`` with an exception set on error, ``0`` on success. This is a convenience function that calls :c:func:`PyUnicode_InternFromString` and :c:func:`PyModule_AddObjectRef`; see their documentation for details. .. c:macro:: PyModule_AddIntMacro(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`` with an exception set on error, ``0`` on success. .. c:macro:: PyModule_AddStringMacro(module, macro) Add a string constant to *module*. .. c:function:: int PyModule_AddType(PyObject *module, PyTypeObject *type) Add a type object to *module*. The type object is finalized by calling internally :c:func:`PyType_Ready`. The name of the type object is taken from the last component of :c:member:`~PyTypeObject.tp_name` after dot. Return ``-1`` with an exception set on error, ``0`` on success. .. versionadded:: 3.9 .. 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`` (such as when using :ref:`multi-phase-initialization`, ``PyModule_Create``, or ``PyModule_FromDefAndSpec``). Some module authors may prefer defining functions in multiple :c:type:`PyMethodDef` arrays; in that case they should call this function directly. The *functions* array must be statically allocated (or otherwise guaranteed to outlive the module object). .. 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`` (such as when using :ref:`multi-phase-initialization`, ``PyModule_Create``, or ``PyModule_FromDefAndSpec``). Return ``0`` on success. Return ``-1`` with an exception set on error. .. versionadded:: 3.5 .. c:function:: int PyUnstable_Module_SetGIL(PyObject *module, void *gil) Indicate that *module* does or does not support running without the global interpreter lock (GIL), using one of the values from :c:macro:`Py_mod_gil`. It must be called during *module*'s initialization function when using :ref:`single-phase-initialization`. If this function is not called during module initialization, the import machinery assumes the module does not support running without the GIL. This function is only available in Python builds configured with :option:`--disable-gil`. Return ``-1`` with an exception set on error, ``0`` on success. .. versionadded:: 3.13 Module lookup (single-phase initialization) ........................................... The legacy :ref:`single-phase initialization <single-phase-initialization>` initialization scheme 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 that uses :ref:`single-phase initialization <single-phase-initialization>`, 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). If a module was attached previously using the same *def*, it is replaced by the new *module*. The caller must have an :term:`attached thread state`. Return ``-1`` with an exception set on error, ``0`` on success. .. versionadded:: 3.3 .. c:function:: int PyState_RemoveModule(PyModuleDef *def) Removes the module object created from *def* from the interpreter state. Return ``-1`` with an exception set on error, ``0`` on success. The caller must have an :term:`attached thread state`. .. versionadded:: 3.3