mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-12-04 00:30:19 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 8

Close #24458: PEP 489 documentation

Browse source 
Patch by Petr Viktorin.
This commit is contained in:
Nick Coghlan 2015-07-03 19:49:15 +10:00
parent ccc897f839
commit 2ab5b092e5
7 changed files with 306 additions and 98 deletions
Download patch file Download diff file Expand all files Collapse all files

2
Doc/c-api/init.rst
View file

@ -873,6 +873,8 @@ been created.
instead.
.. _sub-interpreter-support:
Sub-interpreter support
=======================

320
Doc/c-api/module.rst
View file

@ -82,6 +82,18 @@ Module Objects
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)
@ -107,57 +119,25 @@ Module Objects
unencodable filenames, use :c:func:`PyModule_GetFilenameObject` instead.
Per-interpreter module state
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Single-phase initialization creates singleton modules that can store additional
information as part of the interpreter, allow that state to be retrieved later
with only a reference to the module definition, rather than to the module
itself.
.. 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 with
:c:func:`PyModule_Create`.
.. 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`.
.. versionadded:: 3.3
.. c:function:: int PyState_RemoveModule(PyModuleDef *def)
Removes the module object created from *def* from the interpreter state.
.. versionadded:: 3.3
.. _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 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
This struct holds all information that is needed to create a module object.
There is usually only one static variable of that type for each module, which
is statically initialized and then passed to :c:func:`PyModule_Create` in the
module initialization function.
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
@ -174,19 +154,21 @@ Initializing C modules
.. c:member:: Py_ssize_t m_size
Some modules allow re-initialization (calling their ``PyInit_*`` function
more than once). These modules should keep their state in a per-module
memory area that can be retrieved with :c:func:`PyModule_GetState`.
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 should be used, rather than static globals, to hold per-module
state, since it is then safe for use in multiple sub-interpreters. It is
freed when the module object is deallocated, after the :c:member:`m_free`
function has been called, if present.
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 can not be
re-initialized 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.
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.
@ -198,7 +180,15 @@ Initializing C modules
.. c:member:: PyModuleDef_Slot* m_slots
An array of slot definitions for multi-phase initialization, terminated by
a *NULL* entry.
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
@ -215,20 +205,23 @@ Initializing C modules
A function to call during deallocation of the module object, or *NULL* if
not needed.
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 *module)
.. c:function:: PyObject* PyModule_Create(PyModuleDef *def)
Create a new module object, given the definition in *module*. This behaves
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 *module, int module_api_version)
.. c:function:: PyObject* PyModule_Create2(PyModuleDef *def, int module_api_version)
Create a new module object, given the definition in *module*, assuming the
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.
@ -237,39 +230,179 @@ of the following two module creation functions:
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`.
Alternatively, the module initialization function may instead return a
:c:type:`PyModuleDef` instance with a non-empty ``m_slots`` array. This is
referred to as "multi-phase initialization", and ``PyModuleDef`` instance
should be initialized with the following function:
.. _multi-phase-initialization:
.. c:function:: PyObject* PyModuleDef_Init(PyModuleDef *module)
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.
.. XXX (ncoghlan): It's not clear if it makes sense to document PyModule_ExecDef
PyModule_FromDefAndSpec or PyModule_FromDefAndSpec2 here, as end user code
generally shouldn't be calling those.
Returns *def* cast to ``PyObject*``, or *NULL* if an error occurred.
The module initialization function (if using single phase initialization) or
a function called from a module execution slot (if using multiphase
initialization), can use the following functions to help initialize the module
state:
.. 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_methods``, ``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*. Return ``-1`` on error, ``0``
on success.
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*.
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)
@ -288,7 +421,7 @@ state:
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.
*NULL*-terminated. Return ``-1`` on error, ``0`` on success.
.. c:function:: int PyModule_AddIntMacro(PyObject *module, macro)
@ -302,3 +435,36 @@ state:
.. 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