Module Objects¶

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.