.. highlightlang:: c

.. _importing:

Importing Modules

=================

.. cfunction:: PyObject* PyImport_ImportModule(const char *name)

   .. index::

      single: package variable; __all__

      single: __all__ (package variable)

      single: modules (in module sys)

   This is a simplified interface to :cfunc:`PyImport_ImportModuleEx` below,

   leaving the *globals* and *locals* arguments set to *NULL* and *level* set

   to 0.  When the *name*

   argument contains a dot (when it specifies a submodule of a package), the

   *fromlist* argument is set to the list ``['*']`` so that the return value is the

   named module rather than the top-level package containing it as would otherwise

   be the case.  (Unfortunately, this has an additional side effect when *name* in

   fact specifies a subpackage instead of a submodule: the submodules specified in

   the package's ``__all__`` variable are  loaded.)  Return a new reference to the

   imported module, or *NULL* with an exception set on failure.  Before Python 2.4,

   the module may still be created in the failure case --- examine ``sys.modules``

   to find out.  Starting with Python 2.4, a failing import of a module no longer

   leaves the module in ``sys.modules``.

   .. versionchanged:: 2.4

      failing imports remove incomplete module objects.

   .. versionchanged:: 2.6

      always use absolute imports

.. cfunction:: PyObject* PyImport_ImportModuleNoBlock(const char *name)

   This version of :cfunc:`PyImport_ImportModule` does not block. It's intended

   to be used in C functions that import other modules to execute a function.

   The import may block if another thread holds the import lock. The function

   :cfunc:`PyImport_ImportModuleNoBlock` never blocks. It first tries to fetch

   the module from sys.modules and falls back to :cfunc:`PyImport_ImportModule`

   unless the lock is held, in which case the function will raise an

   :exc:`ImportError`.

   .. versionadded:: 2.6

.. cfunction:: PyObject* PyImport_ImportModuleEx(char *name, PyObject *globals, PyObject *locals, PyObject *fromlist)

   .. index:: builtin: __import__

   Import a module.  This is best described by referring to the built-in Python

   function :func:`__import__`, as the standard :func:`__import__` function calls

   this function directly.

   The return value is a new reference to the imported module or top-level package,

   or *NULL* with an exception set on failure (before Python 2.4, the module may

   still be created in this case).  Like for :func:`__import__`, the return value

   when a submodule of a package was requested is normally the top-level package,

   unless a non-empty *fromlist* was given.

   .. versionchanged:: 2.4

      failing imports remove incomplete module objects.

   .. versionchanged:: 2.6

      The function is an alias for :cfunc:`PyImport_ImportModuleLevel` with

      -1 as level, meaning relative import.

.. cfunction:: PyObject* PyImport_ImportModuleLevel(char *name, PyObject *globals, PyObject *locals, PyObject *fromlist, int level)

   Import a module.  This is best described by referring to the built-in Python

   function :func:`__import__`, as the standard :func:`__import__` function calls

   this function directly.

   The return value is a new reference to the imported module or top-level package,

   or *NULL* with an exception set on failure.  Like for :func:`__import__`,

   the return value when a submodule of a package was requested is normally the

   top-level package, unless a non-empty *fromlist* was given.

   .. versionadded:: 2.5

.. cfunction:: PyObject* PyImport_Import(PyObject *name)

   .. index::

      module: rexec

      module: ihooks

   This is a higher-level interface that calls the current "import hook function".

   It invokes the :func:`__import__` function from the ``__builtins__`` of the

   current globals.  This means that the import is done using whatever import hooks

   are installed in the current environment, e.g. by :mod:`rexec` or :mod:`ihooks`.

   .. versionchanged:: 2.6

      always use absolute imports

.. cfunction:: PyObject* PyImport_ReloadModule(PyObject *m)

   .. index:: builtin: reload

   Reload a module.  This is best described by referring to the built-in Python

   function :func:`reload`, as the standard :func:`reload` function calls this

   function directly.  Return a new reference to the reloaded module, or *NULL*

   with an exception set on failure (the module still exists in this case).

.. cfunction:: PyObject* PyImport_AddModule(const char *name)

   Return the module object corresponding to a module name.  The *name* argument

   may be of the form ``package.module``. First check the modules dictionary if

   there's one there, and if not, create a new one and insert it in the modules

   dictionary. Return *NULL* with an exception set on failure.

   .. note::

      This function does not load or import the module; if the module wasn't already

      loaded, you will get an empty module object. Use :cfunc:`PyImport_ImportModule`

      or one of its variants to import a module.  Package structures implied by a

      dotted name for *name* are not created if not already present.

.. cfunction:: PyObject* PyImport_ExecCodeModule(char *name, PyObject *co)

   .. index:: builtin: compile

   Given a module name (possibly of the form ``package.module``) and a code object

   read from a Python bytecode file or obtained from the built-in function

   :func:`compile`, load the module.  Return a new reference to the module object,

   or *NULL* with an exception set if an error occurred.  Before Python 2.4, the

   module could still be created in error cases.  Starting with Python 2.4, *name*

   is removed from :attr:`sys.modules` in error cases, and even if *name* was already

   in :attr:`sys.modules` on entry to :cfunc:`PyImport_ExecCodeModule`.  Leaving

   incompletely initialized modules in :attr:`sys.modules` is dangerous, as imports of

   such modules have no way to know that the module object is an unknown (and

   probably damaged with respect to the module author's intents) state.

   This function will reload the module if it was already imported.  See

   :cfunc:`PyImport_ReloadModule` for the intended way to reload a module.

   If *name* points to a dotted name of the form ``package.module``, any package

   structures not already created will still not be created.

   .. versionchanged:: 2.4

      *name* is removed from :attr:`sys.modules` in error cases.

.. cfunction:: long PyImport_GetMagicNumber()

   Return the magic number for Python bytecode files (a.k.a. :file:`.pyc` and

   :file:`.pyo` files).  The magic number should be present in the first four bytes

   of the bytecode file, in little-endian byte order.

.. cfunction:: PyObject* PyImport_GetModuleDict()

   Return the dictionary used for the module administration (a.k.a.

   ``sys.modules``).  Note that this is a per-interpreter variable.

.. cfunction:: PyObject* PyImport_GetImporter(PyObject *path)

   Return an importer object for a :data:`sys.path`/:attr:`pkg.__path__` item

   *path*, possibly by fetching it from the :data:`sys.path_importer_cache`

   dict.  If it wasn't yet cached, traverse :data:`sys.path_hooks` until a hook

   is found that can handle the path item.  Return ``None`` if no hook could;

   this tells our caller it should fall back to the builtin import mechanism.

   Cache the result in :data:`sys.path_importer_cache`.  Return a new reference

   to the importer object.

   .. versionadded:: 2.6

.. cfunction:: void _PyImport_Init()

   Initialize the import mechanism.  For internal use only.

.. cfunction:: void PyImport_Cleanup()

   Empty the module table.  For internal use only.

.. cfunction:: void _PyImport_Fini()

   Finalize the import mechanism.  For internal use only.

.. cfunction:: PyObject* _PyImport_FindExtension(char *, char *)

   For internal use only.

.. cfunction:: PyObject* _PyImport_FixupExtension(char *, char *)

   For internal use only.

.. cfunction:: int PyImport_ImportFrozenModule(char *name)

   Load a frozen module named *name*.  Return ``1`` for success, ``0`` if the

   module is not found, and ``-1`` with an exception set if the initialization

   failed.  To access the imported module on a successful load, use

   :cfunc:`PyImport_ImportModule`.  (Note the misnomer --- this function would

   reload the module if it was already imported.)

.. ctype:: struct _frozen

   .. index:: single: freeze utility

   This is the structure type definition for frozen module descriptors, as

   generated by the :program:`freeze` utility (see :file:`Tools/freeze/` in the

   Python source distribution).  Its definition, found in :file:`Include/import.h`,

   is::

      struct _frozen {

          char *name;

          unsigned char *code;

          int size;

      };

.. cvar:: struct _frozen* PyImport_FrozenModules

   This pointer is initialized to point to an array of :ctype:`struct _frozen`

   records, terminated by one whose members are all *NULL* or zero.  When a frozen

   module is imported, it is searched in this table.  Third-party code could play

   tricks with this to provide a dynamically created collection of frozen modules.

.. cfunction:: int PyImport_AppendInittab(char *name, void (*initfunc)(void))

   Add a single module to the existing table of built-in modules.  This is a

   convenience wrapper around :cfunc:`PyImport_ExtendInittab`, returning ``-1`` if

   the table could not be extended.  The new module can be imported by the name

   *name*, and uses the function *initfunc* as the initialization function called

   on the first attempted import.  This should be called before

   :cfunc:`Py_Initialize`.

.. ctype:: struct _inittab

   Structure describing a single entry in the list of built-in modules.  Each of

   these structures gives the name and initialization function for a module built

   into the interpreter.  Programs which embed Python may use an array of these

   structures in conjunction with :cfunc:`PyImport_ExtendInittab` to provide

   additional built-in modules.  The structure is defined in

   :file:`Include/import.h` as::

      struct _inittab {

          char *name;

          void (*initfunc)(void);

      };

.. cfunction:: int PyImport_ExtendInittab(struct _inittab *newtab)

   Add a collection of modules to the table of built-in modules.  The *newtab*

   array must end with a sentinel entry which contains *NULL* for the :attr:`name`

   field; failure to provide the sentinel value can result in a memory fault.

   Returns ``0`` on success or ``-1`` if insufficient memory could be allocated to

   extend the internal table.  In the event of failure, no modules are added to the

   internal table.  This should be called before :cfunc:`Py_Initialize`.