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Multi-phase initialized modules allow m_traverse to be called while the module is still being initialized, so module authors may need to account for that.
479 lines
18 KiB
ReStructuredText
479 lines
18 KiB
ReStructuredText
.. highlightlang:: c
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.. _moduleobjects:
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Module Objects
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--------------
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.. index:: object: module
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.. c:var:: PyTypeObject PyModule_Type
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.. index:: single: ModuleType (in module types)
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This instance of :c:type:`PyTypeObject` represents the Python module type. This
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is exposed to Python programs as ``types.ModuleType``.
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.. c:function:: int PyModule_Check(PyObject *p)
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Return true if *p* is a module object, or a subtype of a module object.
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.. c:function:: int PyModule_CheckExact(PyObject *p)
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Return true if *p* is a module object, but not a subtype of
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:c:data:`PyModule_Type`.
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.. c:function:: PyObject* PyModule_NewObject(PyObject *name)
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.. index::
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single: __name__ (module attribute)
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single: __doc__ (module attribute)
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single: __file__ (module attribute)
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single: __package__ (module attribute)
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single: __loader__ (module attribute)
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Return a new module object with the :attr:`__name__` attribute set to *name*.
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The module's :attr:`__name__`, :attr:`__doc__`, :attr:`__package__`, and
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:attr:`__loader__` attributes are filled in (all but :attr:`__name__` are set
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to ``None``); the caller is responsible for providing a :attr:`__file__`
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attribute.
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.. versionadded:: 3.3
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.. versionchanged:: 3.4
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:attr:`__package__` and :attr:`__loader__` are set to ``None``.
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.. c:function:: PyObject* PyModule_New(const char *name)
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Similar to :c:func:`PyModule_NewObject`, but the name is a UTF-8 encoded
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string instead of a Unicode object.
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.. c:function:: PyObject* PyModule_GetDict(PyObject *module)
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.. index:: single: __dict__ (module attribute)
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Return the dictionary object that implements *module*'s namespace; this object
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is the same as the :attr:`~object.__dict__` attribute of the module object.
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If *module* is not a module object (or a subtype of a module object),
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:exc:`SystemError` is raised and *NULL* is returned.
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It is recommended extensions use other :c:func:`PyModule_\*` and
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:c:func:`PyObject_\*` functions rather than directly manipulate a module's
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:attr:`~object.__dict__`.
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.. c:function:: PyObject* PyModule_GetNameObject(PyObject *module)
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.. index::
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single: __name__ (module attribute)
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single: SystemError (built-in exception)
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Return *module*'s :attr:`__name__` value. If the module does not provide one,
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or if it is not a string, :exc:`SystemError` is raised and *NULL* is returned.
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.. versionadded:: 3.3
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.. c:function:: const char* PyModule_GetName(PyObject *module)
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Similar to :c:func:`PyModule_GetNameObject` but return the name encoded to
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``'utf-8'``.
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.. c:function:: void* PyModule_GetState(PyObject *module)
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Return the "state" of the module, that is, a pointer to the block of memory
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allocated at module creation time, or *NULL*. See
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:c:member:`PyModuleDef.m_size`.
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.. c:function:: PyModuleDef* PyModule_GetDef(PyObject *module)
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Return a pointer to the :c:type:`PyModuleDef` struct from which the module was
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created, or *NULL* if the module wasn't created from a definition.
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.. c:function:: PyObject* PyModule_GetFilenameObject(PyObject *module)
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.. index::
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single: __file__ (module attribute)
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single: SystemError (built-in exception)
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Return the name of the file from which *module* was loaded using *module*'s
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:attr:`__file__` attribute. If this is not defined, or if it is not a
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unicode string, raise :exc:`SystemError` and return *NULL*; otherwise return
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a reference to a Unicode object.
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.. versionadded:: 3.2
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.. c:function:: const char* PyModule_GetFilename(PyObject *module)
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Similar to :c:func:`PyModule_GetFilenameObject` but return the filename
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encoded to 'utf-8'.
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.. deprecated:: 3.2
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:c:func:`PyModule_GetFilename` raises :c:type:`UnicodeEncodeError` on
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unencodable filenames, use :c:func:`PyModule_GetFilenameObject` instead.
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.. _initializing-modules:
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Initializing C modules
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^^^^^^^^^^^^^^^^^^^^^^
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Modules objects are usually created from extension modules (shared libraries
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which export an initialization function), or compiled-in modules
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(where the initialization function is added using :c:func:`PyImport_AppendInittab`).
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See :ref:`building` or :ref:`extending-with-embedding` for details.
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The initialization function can either pass a module definition instance
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to :c:func:`PyModule_Create`, and return the resulting module object,
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or request "multi-phase initialization" by returning the definition struct itself.
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.. c:type:: PyModuleDef
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The module definition struct, which holds all information needed to create
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a module object. There is usually only one statically initialized variable
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of this type for each module.
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.. c:member:: PyModuleDef_Base m_base
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Always initialize this member to :const:`PyModuleDef_HEAD_INIT`.
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.. c:member:: const char *m_name
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Name for the new module.
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.. c:member:: const char *m_doc
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Docstring for the module; usually a docstring variable created with
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:c:func:`PyDoc_STRVAR` is used.
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.. c:member:: Py_ssize_t m_size
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Module state may be kept in a per-module memory area that can be
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retrieved with :c:func:`PyModule_GetState`, rather than in static globals.
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This makes modules safe for use in multiple sub-interpreters.
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This memory area is allocated based on *m_size* on module creation,
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and freed when the module object is deallocated, after the
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:c:member:`m_free` function has been called, if present.
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Setting ``m_size`` to ``-1`` means that the module does not support
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sub-interpreters, because it has global state.
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Setting it to a non-negative value means that the module can be
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re-initialized and specifies the additional amount of memory it requires
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for its state. Non-negative ``m_size`` is required for multi-phase
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initialization.
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See :PEP:`3121` for more details.
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.. c:member:: PyMethodDef* m_methods
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A pointer to a table of module-level functions, described by
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:c:type:`PyMethodDef` values. Can be *NULL* if no functions are present.
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.. c:member:: PyModuleDef_Slot* m_slots
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An array of slot definitions for multi-phase initialization, terminated by
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a ``{0, NULL}`` entry.
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When using single-phase initialization, *m_slots* must be *NULL*.
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.. versionchanged:: 3.5
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Prior to version 3.5, this member was always set to *NULL*,
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and was defined as:
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.. c:member:: inquiry m_reload
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.. c:member:: traverseproc m_traverse
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A traversal function to call during GC traversal of the module object, or
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*NULL* if not needed. This function may be called before module state
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is allocated (:c:func:`PyModule_GetState()` may return `NULL`),
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and before the :c:member:`Py_mod_exec` function is executed.
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.. c:member:: inquiry m_clear
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A clear function to call during GC clearing of the module object, or
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*NULL* if not needed. This function may be called before module state
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is allocated (:c:func:`PyModule_GetState()` may return `NULL`),
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and before the :c:member:`Py_mod_exec` function is executed.
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.. c:member:: freefunc m_free
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A function to call during deallocation of the module object, or *NULL* if
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not needed. This function may be called before module state
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is allocated (:c:func:`PyModule_GetState()` may return `NULL`),
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and before the :c:member:`Py_mod_exec` function is executed.
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Single-phase initialization
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...........................
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The module initialization function may create and return the module object
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directly. This is referred to as "single-phase initialization", and uses one
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of the following two module creation functions:
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.. c:function:: PyObject* PyModule_Create(PyModuleDef *def)
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Create a new module object, given the definition in *def*. This behaves
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like :c:func:`PyModule_Create2` with *module_api_version* set to
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:const:`PYTHON_API_VERSION`.
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.. c:function:: PyObject* PyModule_Create2(PyModuleDef *def, int module_api_version)
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Create a new module object, given the definition in *def*, assuming the
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API version *module_api_version*. If that version does not match the version
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of the running interpreter, a :exc:`RuntimeWarning` is emitted.
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.. note::
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Most uses of this function should be using :c:func:`PyModule_Create`
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instead; only use this if you are sure you need it.
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Before it is returned from in the initialization function, the resulting module
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object is typically populated using functions like :c:func:`PyModule_AddObject`.
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.. _multi-phase-initialization:
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Multi-phase initialization
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..........................
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An alternate way to specify extensions is to request "multi-phase initialization".
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Extension modules created this way behave more like Python modules: the
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initialization is split between the *creation phase*, when the module object
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is created, and the *execution phase*, when it is populated.
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The distinction is similar to the :py:meth:`__new__` and :py:meth:`__init__` methods
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of classes.
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Unlike modules created using single-phase initialization, these modules are not
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singletons: if the *sys.modules* entry is removed and the module is re-imported,
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a new module object is created, and the old module is subject to normal garbage
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collection -- as with Python modules.
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By default, multiple modules created from the same definition should be
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independent: changes to one should not affect the others.
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This means that all state should be specific to the module object (using e.g.
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using :c:func:`PyModule_GetState`), or its contents (such as the module's
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:attr:`__dict__` or individual classes created with :c:func:`PyType_FromSpec`).
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All modules created using multi-phase initialization are expected to support
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:ref:`sub-interpreters <sub-interpreter-support>`. Making sure multiple modules
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are independent is typically enough to achieve this.
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To request multi-phase initialization, the initialization function
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(PyInit_modulename) returns a :c:type:`PyModuleDef` instance with non-empty
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:c:member:`~PyModuleDef.m_slots`. Before it is returned, the ``PyModuleDef``
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instance must be initialized with the following function:
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.. c:function:: PyObject* PyModuleDef_Init(PyModuleDef *def)
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Ensures a module definition is a properly initialized Python object that
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correctly reports its type and reference count.
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Returns *def* cast to ``PyObject*``, or *NULL* if an error occurred.
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.. versionadded:: 3.5
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The *m_slots* member of the module definition must point to an array of
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``PyModuleDef_Slot`` structures:
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.. c:type:: PyModuleDef_Slot
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.. c:member:: int slot
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A slot ID, chosen from the available values explained below.
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.. c:member:: void* value
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Value of the slot, whose meaning depends on the slot ID.
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.. versionadded:: 3.5
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The *m_slots* array must be terminated by a slot with id 0.
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The available slot types are:
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.. c:var:: Py_mod_create
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Specifies a function that is called to create the module object itself.
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The *value* pointer of this slot must point to a function of the signature:
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.. c:function:: PyObject* create_module(PyObject *spec, PyModuleDef *def)
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The function receives a :py:class:`~importlib.machinery.ModuleSpec`
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instance, as defined in :PEP:`451`, and the module definition.
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It should return a new module object, or set an error
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and return *NULL*.
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This function should be kept minimal. In particular, it should not
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call arbitrary Python code, as trying to import the same module again may
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result in an infinite loop.
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Multiple ``Py_mod_create`` slots may not be specified in one module
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definition.
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If ``Py_mod_create`` is not specified, the import machinery will create
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a normal module object using :c:func:`PyModule_New`. The name is taken from
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*spec*, not the definition, to allow extension modules to dynamically adjust
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to their place in the module hierarchy and be imported under different
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names through symlinks, all while sharing a single module definition.
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There is no requirement for the returned object to be an instance of
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:c:type:`PyModule_Type`. Any type can be used, as long as it supports
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setting and getting import-related attributes.
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However, only ``PyModule_Type`` instances may be returned if the
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``PyModuleDef`` has non-*NULL* ``m_traverse``, ``m_clear``,
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``m_free``; non-zero ``m_size``; or slots other than ``Py_mod_create``.
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.. c:var:: Py_mod_exec
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Specifies a function that is called to *execute* the module.
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This is equivalent to executing the code of a Python module: typically,
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this function adds classes and constants to the module.
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The signature of the function is:
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.. c:function:: int exec_module(PyObject* module)
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If multiple ``Py_mod_exec`` slots are specified, they are processed in the
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order they appear in the *m_slots* array.
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See :PEP:`489` for more details on multi-phase initialization.
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Low-level module creation functions
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...................................
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The following functions are called under the hood when using multi-phase
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initialization. They can be used directly, for example when creating module
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objects dynamically. Note that both ``PyModule_FromDefAndSpec`` and
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``PyModule_ExecDef`` must be called to fully initialize a module.
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.. c:function:: PyObject * PyModule_FromDefAndSpec(PyModuleDef *def, PyObject *spec)
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Create a new module object, given the definition in *module* and the
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ModuleSpec *spec*. This behaves like :c:func:`PyModule_FromDefAndSpec2`
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with *module_api_version* set to :const:`PYTHON_API_VERSION`.
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.. versionadded:: 3.5
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.. c:function:: PyObject * PyModule_FromDefAndSpec2(PyModuleDef *def, PyObject *spec, int module_api_version)
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Create a new module object, given the definition in *module* and the
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ModuleSpec *spec*, assuming the API version *module_api_version*.
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If that version does not match the version of the running interpreter,
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a :exc:`RuntimeWarning` is emitted.
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.. note::
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Most uses of this function should be using :c:func:`PyModule_FromDefAndSpec`
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instead; only use this if you are sure you need it.
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.. versionadded:: 3.5
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.. c:function:: int PyModule_ExecDef(PyObject *module, PyModuleDef *def)
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Process any execution slots (:c:data:`Py_mod_exec`) given in *def*.
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.. versionadded:: 3.5
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.. c:function:: int PyModule_SetDocString(PyObject *module, const char *docstring)
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Set the docstring for *module* to *docstring*.
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This function is called automatically when creating a module from
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``PyModuleDef``, using either ``PyModule_Create`` or
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``PyModule_FromDefAndSpec``.
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.. versionadded:: 3.5
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.. c:function:: int PyModule_AddFunctions(PyObject *module, PyMethodDef *functions)
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Add the functions from the *NULL* terminated *functions* array to *module*.
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Refer to the :c:type:`PyMethodDef` documentation for details on individual
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entries (due to the lack of a shared module namespace, module level
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"functions" implemented in C typically receive the module as their first
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parameter, making them similar to instance methods on Python classes).
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This function is called automatically when creating a module from
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``PyModuleDef``, using either ``PyModule_Create`` or
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``PyModule_FromDefAndSpec``.
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.. versionadded:: 3.5
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Support functions
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.................
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The module initialization function (if using single phase initialization) or
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a function called from a module execution slot (if using multi-phase
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initialization), can use the following functions to help initialize the module
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state:
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.. c:function:: int PyModule_AddObject(PyObject *module, const char *name, PyObject *value)
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Add an object to *module* as *name*. This is a convenience function which can
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be used from the module's initialization function. This steals a reference to
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*value*. Return ``-1`` on error, ``0`` on success.
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.. c:function:: int PyModule_AddIntConstant(PyObject *module, const char *name, long value)
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Add an integer constant to *module* as *name*. This convenience function can be
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used from the module's initialization function. Return ``-1`` on error, ``0`` on
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success.
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.. c:function:: int PyModule_AddStringConstant(PyObject *module, const char *name, const char *value)
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Add a string constant to *module* as *name*. This convenience function can be
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used from the module's initialization function. The string *value* must be
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*NULL*-terminated. Return ``-1`` on error, ``0`` on success.
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.. c:function:: int PyModule_AddIntMacro(PyObject *module, macro)
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Add an int constant to *module*. The name and the value are taken from
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*macro*. For example ``PyModule_AddIntMacro(module, AF_INET)`` adds the int
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constant *AF_INET* with the value of *AF_INET* to *module*.
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Return ``-1`` on error, ``0`` on success.
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.. c:function:: int PyModule_AddStringMacro(PyObject *module, macro)
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Add a string constant to *module*.
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Module lookup
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^^^^^^^^^^^^^
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Single-phase initialization creates singleton modules that can be looked up
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in the context of the current interpreter. This allows the module object to be
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retrieved later with only a reference to the module definition.
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These functions will not work on modules created using multi-phase initialization,
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since multiple such modules can be created from a single definition.
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.. c:function:: PyObject* PyState_FindModule(PyModuleDef *def)
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Returns the module object that was created from *def* for the current interpreter.
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This method requires that the module object has been attached to the interpreter state with
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:c:func:`PyState_AddModule` beforehand. In case the corresponding module object is not
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found or has not been attached to the interpreter state yet, it returns *NULL*.
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.. c:function:: int PyState_AddModule(PyObject *module, PyModuleDef *def)
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Attaches the module object passed to the function to the interpreter state. This allows
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the module object to be accessible via :c:func:`PyState_FindModule`.
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Only effective on modules created using single-phase initialization.
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.. versionadded:: 3.3
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.. c:function:: int PyState_RemoveModule(PyModuleDef *def)
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Removes the module object created from *def* from the interpreter state.
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.. versionadded:: 3.3
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