Module Objects — Python 3.9.0 documentation

# Module Objects

PyTypeObject `PyModule_Type`

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

int `PyModule_Check`(PyObject *p)

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

int `PyModule_CheckExact`(PyObject *p)

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

PyObject* `PyModule_NewObject`(PyObject *name)
  Return value: New reference.

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

  New in version 3.3.

  Changed in version 3.4: `__package__` and `__loader__` are set to `None`.

PyObject* `PyModule_New`(const char *name)
  Return value: New reference.

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

PyObject* `PyModule_GetDict`(PyObject *module)
  Return value: Borrowed reference.

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

  It is recommended extensions use other `PyModule_*()` and `PyObject_*()` functions rather than directly manipulate a module’s `__dict__`.

PyObject* `PyModule_GetNameObject`(PyObject *module)
  Return value: New reference.

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

  New in version 3.3.

const char* `PyModule_GetName`(PyObject *module)

  Similar to `PyModule_GetNameObject()` but return the name encoded to `'utf-8'`.

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 `PyModuleDef.m_size`.

PyModuleDef* `PyModule_GetDef`(PyObject *module)

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

PyObject* `PyModule_GetFilenameObject`(PyObject *module)
  Return value: New reference.

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

  New in version 3.2.

const char* `PyModule_GetFilename`(PyObject *module)

  Similar to `PyModule_GetFilenameObject()` but return the filename encoded to ‘utf-8’.

  Deprecated since version 3.2: `PyModule_GetFilename()` raises `UnicodeEncodeError` on unencodable filenames, use `PyModule_GetFilenameObject()` instead.

## 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 `PyImport_AppendInittab()`). See Building C and C++ Extensions or Extending Embedded Python for details.

The initialization function can either pass a module definition instance to `PyModule_Create()`, and return the resulting module object, or request “multi-phase initialization” by returning the definition struct itself.

`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.

  PyModuleDef_Base `m_base`

    Always initialize this member to `PyModuleDef_HEAD_INIT`.

  const char *`m_name`

    Name for the new module.

  const char *`m_doc`

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

  Py_ssize_t `m_size`

    Module state may be kept in a per-module memory area that can be retrieved with `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 `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.

  PyMethodDef* `m_methods`

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

  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`.

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

    > inquiry `m_reload`

  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 (`Py_mod_exec` function). More precisely, this function is not called if `m_size` is greater than 0 and the module state (as returned by `PyModule_GetState()`) is `NULL`.

    Changed in version 3.9: No longer called before the module state is allocated.

  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 (`Py_mod_exec` function). More precisely, this function is not called if `m_size` is greater than 0 and the module state (as returned by `PyModule_GetState()`) is `NULL`.

    Changed in version 3.9: No longer called before the module state is allocated.

  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 (`Py_mod_exec` function). More precisely, this function is not called if `m_size` is greater than 0 and the module state (as returned by `PyModule_GetState()`) is `NULL`.

    Changed in version 3.9: No longer called before the module state is allocated.

### 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:

PyObject* `PyModule_Create`(PyModuleDef *def)
  Return value: New reference.

  Create a new module object, given the definition in def. This behaves like `PyModule_Create2()` with module_api_version set to `PYTHON_API_VERSION`.

PyObject* `PyModule_Create2`(PyModuleDef *def, int module_api_version)
  Return value: New reference.

  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 `RuntimeWarning` is emitted.

  Note

  Most uses of this function should be using `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 `PyModule_AddObject()`.

### 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 `__new__()` and `__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 `PyModule_GetState()`), or its contents (such as the module’s `__dict__` or individual classes created with `PyType_FromSpec()`).

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

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

PyObject* `PyModuleDef_Init`(PyModuleDef *def)
  Return value: Borrowed reference.

  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.

  New in version 3.5.

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

`PyModuleDef_Slot`
  int `slot`

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

  void* `value`

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

  New in version 3.5.

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

The available slot types are:

`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:

  PyObject* `create_module`(PyObject *spec, PyModuleDef *def)

  The function receives a `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 `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 `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`.

`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:

  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.

PyObject * `PyModule_FromDefAndSpec`(PyModuleDef *def, PyObject *spec)
  Return value: New reference.

  Create a new module object, given the definition in module and the ModuleSpec spec. This behaves like `PyModule_FromDefAndSpec2()` with module_api_version set to `PYTHON_API_VERSION`.

  New in version 3.5.

PyObject * `PyModule_FromDefAndSpec2`(PyModuleDef *def, PyObject *spec, int module_api_version)
  Return value: New reference.

  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 `RuntimeWarning` is emitted.

  Note

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

  New in version 3.5.

int `PyModule_ExecDef`(PyObject *module, PyModuleDef *def)

  Process any execution slots (`Py_mod_exec`) given in def.

  New in version 3.5.

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`.

  New in version 3.5.

int `PyModule_AddFunctions`(PyObject *module, PyMethodDef *functions)

  Add the functions from the `NULL` terminated functions array to module. Refer to the `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`.

  New in version 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:

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 `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;
      }

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.

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.

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.

int `PyModule_AddStringMacro`(PyObject *module, macro)

  Add a string constant to module.

int `PyModule_AddType`(PyObject *module, PyTypeObject *type)

  Add a type object to module. The type object is finalized by calling internally `PyType_Ready()`. The name of the type object is taken from the last component of `tp_name` after dot. Return `-1` on error, `0` on success.

  New in version 3.9.

## 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.

PyObject* `PyState_FindModule`(PyModuleDef *def)
  Return value: Borrowed reference.

  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 `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`.

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 `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).

  The caller must hold the GIL.

  Return 0 on success or -1 on failure.

  New in version 3.3.

int `PyState_RemoveModule`(PyModuleDef *def)

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

  The caller must hold the GIL.

  New in version 3.3.