5.3 Importing Modules

Python PEP

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5.3 Importing Modules

PyObject* PyImport_ImportModule( char *name): Return value: New reference.
This is a simplified interface to PyImport_ImportModuleEx() below, leaving the globals and locals arguments set to NULL. 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. Changed in version 2.4: failing imports remove incomplete module objects.

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 (before Python 2.4, the module may still be created in this case). 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. Changed in version 2.4: failing imports remove incomplete module objects.

PyObject* PyImport_Import( PyObject *name): Return value: New reference.
This is a higher-level interface that calls the current ``import hook function''. 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, e.g. by rexec or ihooks.

PyObject* PyImport_ReloadModule( PyObject *m): Return value: New reference.
Reload a module. This is best described by referring to the built-in Python function reload(), as the standard 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).

PyObject* PyImport_AddModule( 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. Before Python 2.4, the module could still be created in error cases. Starting with Python 2.4, name is removed from sys.modules in error cases, and 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.

Changed in version 2.4: name is removed from sys.modules in error cases.

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.

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 *): Return value: Borrowed reference.
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, void (*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;
    void (*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().

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