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:mod:`pkgutil` --- Package extension utility
============================================
.. module:: pkgutil
:synopsis: Utilities for the import system.
**Source code:** :source:`Lib/pkgutil.py`
--------------
This module provides utilities for the import system, in particular package
support.
.. function:: extend_path(path, name)
Extend the search path for the modules which comprise a package. Intended
use is to place the following code in a package's :file:`__init__.py`::
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)
This will add to the package's ``__path__`` all subdirectories of directories
on ``sys.path`` named after the package. This is useful if one wants to
distribute different parts of a single logical package as multiple
directories.
It also looks for :file:`\*.pkg` files beginning where ``*`` matches the
*name* argument. This feature is similar to :file:`\*.pth` files (see the
:mod:`site` module for more information), except that it doesn't special-case
lines starting with ``import``. A :file:`\*.pkg` file is trusted at face
value: apart from checking for duplicates, all entries found in a
:file:`\*.pkg` file are added to the path, regardless of whether they exist
on the filesystem. (This is a feature.)
If the input path is not a list (as is the case for frozen packages) it is
returned unchanged. The input path is not modified; an extended copy is
returned. Items are only appended to the copy at the end.
It is assumed that :data:`sys.path` is a sequence. Items of :data:`sys.path`
that are not strings referring to existing directories are ignored. Unicode
items on :data:`sys.path` that cause errors when used as filenames may cause
this function to raise an exception (in line with :func:`os.path.isdir`
behavior).
.. class:: ImpImporter(dirname=None)
:pep:`302` Importer that wraps Python's "classic" import algorithm.
If *dirname* is a string, a :pep:`302` importer is created that searches that
directory. If *dirname* is ``None``, a :pep:`302` importer is created that
searches the current :data:`sys.path`, plus any modules that are frozen or
built-in.
Note that :class:`ImpImporter` does not currently support being used by
placement on :data:`sys.meta_path`.
.. class:: ImpLoader(fullname, file, filename, etc)
:pep:`302` Loader that wraps Python's "classic" import algorithm.
.. function:: find_loader(fullname)
Find a :pep:`302` "loader" object for *fullname*.
If *fullname* contains dots, path must be the containing package's
``__path__``. Returns ``None`` if the module cannot be found or imported.
This function uses :func:`iter_importers`, and is thus subject to the same
limitations regarding platform-specific special import locations such as the
Windows registry.
.. function:: get_importer(path_item)
Retrieve a :pep:`302` importer for the given *path_item*.
The returned importer is cached in :data:`sys.path_importer_cache` if it was
newly created by a path hook.
If there is no importer, a wrapper around the basic import machinery is
returned. This wrapper is never inserted into the importer cache (``None``
is inserted instead).
The cache (or part of it) can be cleared manually if a rescan of
:data:`sys.path_hooks` is necessary.
.. function:: get_loader(module_or_name)
Get a :pep:`302` "loader" object for *module_or_name*.
If the module or package is accessible via the normal import mechanism, a
wrapper around the relevant part of that machinery is returned. Returns
``None`` if the module cannot be found or imported. If the named module is
not already imported, its containing package (if any) is imported, in order
to establish the package ``__path__``.
This function uses :func:`iter_importers`, and is thus subject to the same
limitations regarding platform-specific special import locations such as the
Windows registry.
.. function:: iter_importers(fullname='')
Yield :pep:`302` importers for the given module name.
If fullname contains a '.', the importers will be for the package containing
fullname, otherwise they will be importers for :data:`sys.meta_path`,
:data:`sys.path`, and Python's "classic" import machinery, in that order. If
the named module is in a package, that package is imported as a side effect
of invoking this function.
Non-:pep:`302` mechanisms (e.g. the Windows registry) used by the standard
import machinery to find files in alternative locations are partially
supported, but are searched *after* :data:`sys.path`. Normally, these
locations are searched *before* :data:`sys.path`, preventing :data:`sys.path`
entries from shadowing them.
For this to cause a visible difference in behaviour, there must be a module
or package name that is accessible via both :data:`sys.path` and one of the
non-:pep:`302` file system mechanisms. In this case, the emulation will find
the former version, while the builtin import mechanism will find the latter.
Items of the following types can be affected by this discrepancy:
``imp.C_EXTENSION``, ``imp.PY_SOURCE``, ``imp.PY_COMPILED``,
``imp.PKG_DIRECTORY``.
.. function:: iter_modules(path=None, prefix='')
Yields ``(module_loader, name, ispkg)`` for all submodules on *path*, or, if
path is ``None``, all top-level modules on ``sys.path``.
*path* should be either ``None`` or a list of paths to look for modules in.
*prefix* is a string to output on the front of every module name on output.
.. note::
Only works for importers which define a ``iter_modules()`` method, which
is non-standard but implemented by classes defined in this module.
.. function:: walk_packages(path=None, prefix='', onerror=None)
Yields ``(module_loader, name, ispkg)`` for all modules recursively on
*path*, or, if path is ``None``, all accessible modules.
*path* should be either ``None`` or a list of paths to look for modules in.
*prefix* is a string to output on the front of every module name on output.
Note that this function must import all *packages* (*not* all modules!) on
the given *path*, in order to access the ``__path__`` attribute to find
submodules.
*onerror* is a function which gets called with one argument (the name of the
package which was being imported) if any exception occurs while trying to
import a package. If no *onerror* function is supplied, :exc:`ImportError`\s
are caught and ignored, while all other exceptions are propagated,
terminating the search.
Examples::
# list all modules python can access
walk_packages()
# list all submodules of ctypes
walk_packages(ctypes.__path__, ctypes.__name__ + '.')
.. note::
Only works for importers which define a ``iter_modules()`` method, which
is non-standard but implemented by classes defined in this module.
.. function:: get_data(package, resource)
Get a resource from a package.
This is a wrapper for the :pep:`302` loader :func:`get_data` API. The
*package* argument should be the name of a package, in standard module format
(``foo.bar``). The *resource* argument should be in the form of a relative
filename, using ``/`` as the path separator. The parent directory name
``..`` is not allowed, and nor is a rooted name (starting with a ``/``).
The function returns a binary string that is the contents of the specified
resource.
For packages located in the filesystem, which have already been imported,
this is the rough equivalent of::
d = os.path.dirname(sys.modules[package].__file__)
data = open(os.path.join(d, resource), 'rb').read()
If the package cannot be located or loaded, or it uses a :pep:`302` loader
which does not support :func:`get_data`, then ``None`` is returned.
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