1 .. highlightlang:: c

     2 

     3 .. _importing:

     4 

     5 Importing Modules

     6 =================

     7 

     8 

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

    10 

    11    .. index::

    12       single: package variable; __all__

    13       single: __all__ (package variable)

    14       single: modules (in module sys)

    15 

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

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

    18    to 0.  When the *name*

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

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

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

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

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

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

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

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

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

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

    29 

    30    .. versionchanged:: 2.4

    31       failing imports remove incomplete module objects.

    32 

    33    .. versionchanged:: 2.6

    34       always use absolute imports

    35 

    36 

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

    38 

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

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

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

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

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

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

    45    :exc:`ImportError`.

    46 

    47    .. versionadded:: 2.6

    48 

    49 

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

    51 

    52    .. index:: builtin: __import__

    53 

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

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

    56    this function directly.

    57 

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

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

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

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

    62    unless a non-empty *fromlist* was given.

    63 

    64    .. versionchanged:: 2.4

    65       failing imports remove incomplete module objects.

    66 

    67    .. versionchanged:: 2.6

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

    69       -1 as level, meaning relative import.

    70 

    71 

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

    73 

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

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

    76    this function directly.

    77 

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

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

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

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

    82 

    83    .. versionadded:: 2.5

    84 

    85 

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

    87 

    88    .. index::

    89       module: rexec

    90       module: ihooks

    91 

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

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

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

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

    96 

    97    .. versionchanged:: 2.6

    98       always use absolute imports

    99 

   100 

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

   102 

   103    .. index:: builtin: reload

   104 

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

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

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

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

   109 

   110 

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

   112 

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

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

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

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

   117 

   118    .. note::

   119 

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

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

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

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

   124 

   125 

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

   127 

   128    .. index:: builtin: compile

   129 

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

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

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

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

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

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

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

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

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

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

   140 

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

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

   143 

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

   145    structures not already created will still not be created.

   146 

   147    .. versionchanged:: 2.4

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

   149 

   150 

   151 .. cfunction:: long PyImport_GetMagicNumber()

   152 

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

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

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

   156 

   157 

   158 .. cfunction:: PyObject* PyImport_GetModuleDict()

   159 

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

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

   162 

   163 

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

   165 

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

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

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

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

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

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

   172    to the importer object.

   173 

   174    .. versionadded:: 2.6

   175 

   176 

   177 .. cfunction:: void _PyImport_Init()

   178 

   179    Initialize the import mechanism.  For internal use only.

   180 

   181 

   182 .. cfunction:: void PyImport_Cleanup()

   183 

   184    Empty the module table.  For internal use only.

   185 

   186 

   187 .. cfunction:: void _PyImport_Fini()

   188 

   189    Finalize the import mechanism.  For internal use only.

   190 

   191 

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

   193 

   194    For internal use only.

   195 

   196 

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

   198 

   199    For internal use only.

   200 

   201 

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

   203 

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

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

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

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

   208    reload the module if it was already imported.)

   209 

   210 

   211 .. ctype:: struct _frozen

   212 

   213    .. index:: single: freeze utility

   214 

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

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

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

   218    is::

   219 

   220       struct _frozen {

   221           char *name;

   222           unsigned char *code;

   223           int size;

   224       };

   225 

   226 

   227 .. cvar:: struct _frozen* PyImport_FrozenModules

   228 

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

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

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

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

   233 

   234 

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

   236 

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

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

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

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

   241    on the first attempted import.  This should be called before

   242    :cfunc:`Py_Initialize`.

   243 

   244 

   245 .. ctype:: struct _inittab

   246 

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

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

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

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

   251    additional built-in modules.  The structure is defined in

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

   253 

   254       struct _inittab {

   255           char *name;

   256           void (*initfunc)(void);

   257       };

   258 

   259 

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

   261 

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

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

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

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

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

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