Edit File: import.txt
.. highlightlang:: c .. _importing: Importing Modules ================= .. c:function:: 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 :c:func:`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 uses absolute imports. .. c:function:: PyObject* PyImport_ImportModuleNoBlock(const char *name) This version of :c:func:`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 :c:func:`PyImport_ImportModuleNoBlock` never blocks. It first tries to fetch the module from sys.modules and falls back to :c:func:`PyImport_ImportModule` unless the lock is held, in which case the function will raise an :exc:`ImportError`. .. versionadded:: 2.6 .. c:function:: 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 :c:func:`PyImport_ImportModuleLevel` with -1 as level, meaning relative import. .. c:function:: 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 .. c:function:: 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 uses absolute imports. .. c:function:: 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). .. c:function:: 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 :c:func:`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. .. c:function:: 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 :c:func:`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. The module's :attr:`__file__` attribute will be set to the code object's :c:member:`co_filename`. This function will reload the module if it was already imported. See :c:func:`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. .. c:function:: PyObject* PyImport_ExecCodeModuleEx(char *name, PyObject *co, char *pathname) Like :c:func:`PyImport_ExecCodeModule`, but the :attr:`__file__` attribute of the module object is set to *pathname* if it is non-``NULL``. .. c:function:: 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. .. c:function:: PyObject* PyImport_GetModuleDict() Return the dictionary used for the module administration (a.k.a. ``sys.modules``). Note that this is a per-interpreter variable. .. c:function:: 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 built-in import mechanism. Cache the result in :data:`sys.path_importer_cache`. Return a new reference to the importer object. .. versionadded:: 2.6 .. c:function:: void _PyImport_Init() Initialize the import mechanism. For internal use only. .. c:function:: void PyImport_Cleanup() Empty the module table. For internal use only. .. c:function:: void _PyImport_Fini() Finalize the import mechanism. For internal use only. .. c:function:: PyObject* _PyImport_FindExtension(char *, char *) For internal use only. .. c:function:: PyObject* _PyImport_FixupExtension(char *, char *) For internal use only. .. c:function:: 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 :c:func:`PyImport_ImportModule`. (Note the misnomer --- this function would reload the module if it was already imported.) .. c:type:: 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; }; .. c:var:: struct _frozen* PyImport_FrozenModules This pointer is initialized to point to an array of :c:type:`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. .. c:function:: int PyImport_AppendInittab(const char *name, void (*initfunc)(void)) Add a single module to the existing table of built-in modules. This is a convenience wrapper around :c:func:`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 :c:func:`Py_Initialize`. .. c:type:: 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 :c:func:`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); }; .. c:function:: 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 :c:func:`Py_Initialize`.