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Module Objects

kbe/src/lib/python/Doc/c-api/module.rst

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.. highlightlang:: 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. Return -1 on error, 0 on success.

.. 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.

.. versionadded:: 3.3

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

Removes the module object created from def from the interpreter state.

.. versionadded:: 3.3