
Importing Modules
*****************

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

   This is a simplified interface to ``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.  A
   failing import of a module doesn't leave the module in
   ``sys.modules``.

PyObject* PyImport_ImportModuleNoBlock(const char *name)

   This version of ``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 ``PyImport_ImportModuleNoBlock``
   never blocks. It first tries to fetch the module from sys.modules
   and falls back to ``PyImport_ImportModule`` unless the lock is
   held, in which case the function will raise an ``ImportError``.

PyObject* PyImport_ImportModuleEx(char *name, PyObject *globals, PyObject *locals, PyObject *fromlist)
    Return value: New reference.

   Import a module.  This is best described by referring to the built-
   in Python function ``__import__()``, as the standard
   ``__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 ``__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.

   Failing imports remove incomplete module objects, like with
   ``PyImport_ImportModule``.

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 ``__import__()``, as the standard
   ``__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 ``__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.

PyObject* PyImport_Import(PyObject *name)
    Return value: New reference.

   This is a higher-level interface that calls the current "import
   hook function" (with an explicit *level* of 0, meaning absolute
   import).  It invokes the ``__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.

PyObject* PyImport_ReloadModule(PyObject *m)
    Return value: New reference.

   Reload a module.  Return a new reference to the reloaded module, or
   *NULL* with an exception set on failure (the module still exists in
   this case).

PyObject* PyImport_AddModule(const char *name)
    Return value: Borrowed reference.

   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
     ``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.

PyObject* PyImport_ExecCodeModule(char *name, PyObject *co)
    Return value: New reference.

   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 ``compile()``, load the module.  Return a new
   reference to the module object, or *NULL* with an exception set if
   an error occurred.  *name* is removed from ``sys.modules`` in error
   cases, even if *name* was already in ``sys.modules`` on entry to
   ``PyImport_ExecCodeModule``.  Leaving incompletely initialized
   modules in ``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 ``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.

long PyImport_GetMagicNumber()

   Return the magic number for Python bytecode files (a.k.a. ``.pyc``
   and ``.pyo`` files).  The magic number should be present in the
   first four bytes of the bytecode file, in little-endian byte order.

PyObject* PyImport_GetModuleDict()
    Return value: Borrowed reference.

   Return the dictionary used for the module administration (a.k.a.
   ``sys.modules``).  Note that this is a per-interpreter variable.

PyObject* PyImport_GetImporter(PyObject *path)

   Return an importer object for a ``sys.path``/``pkg.__path__`` item
   *path*, possibly by fetching it from the
   ``sys.path_importer_cache`` dict.  If it wasn't yet cached,
   traverse ``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 ``sys.path_importer_cache``.  Return a new reference
   to the importer object.

void _PyImport_Init()

   Initialize the import mechanism.  For internal use only.

void PyImport_Cleanup()

   Empty the module table.  For internal use only.

void _PyImport_Fini()

   Finalize the import mechanism.  For internal use only.

PyObject* _PyImport_FindExtension(char *, char *)

   For internal use only.

PyObject* _PyImport_FixupExtension(char *, char *)

   For internal use only.

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 ``PyImport_ImportModule``.  (Note the misnomer
   --- this function would reload the module if it was already
   imported.)

struct _frozen

   This is the structure type definition for frozen module
   descriptors, as generated by the **freeze** utility (see
   ``Tools/freeze/`` in the Python source distribution).  Its
   definition, found in ``Include/import.h``, is:

      struct _frozen {
          char *name;
          unsigned char *code;
          int size;
      };

struct _frozen* PyImport_FrozenModules

   This pointer is initialized to point to an array of ``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.

int PyImport_AppendInittab(char *name, PyObject* (*initfunc)(void))

   Add a single module to the existing table of built-in modules.
   This is a convenience wrapper around ``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 ``Py_Initialize``.

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 ``PyImport_ExtendInittab`` to provide additional
   built-in modules.  The structure is defined in ``Include/import.h``
   as:

      struct _inittab {
          char *name;
          PyObject* (*initfunc)(void);
      };

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 ``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 ``Py_Initialize``.
