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. This function always succeeds.

int PyModule_CheckExact(PyObject *p)

   Return true if *p* is a module object, but not a subtype of
   "PyModule_Type".  This function always succeeds.

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".

      Like "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
      "m_free" is called directly.

      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.
