#7303: add documentation for useful pkgutil functions and classes.
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Georg Brandl
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============================================
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.. module:: pkgutil
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:synopsis: Utilities to support extension of packages.
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:synopsis: Utilities for the import system.
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This module provides functions to manipulate packages:
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This module provides utilities for the import system, in particular package
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support.
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.. function:: extend_path(path, name)
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Extend the search path for the modules which comprise a package. Intended use is
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to place the following code in a package's :file:`__init__.py`::
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Extend the search path for the modules which comprise a package. Intended
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use is to place the following code in a package's :file:`__init__.py`::
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from pkgutil import extend_path
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__path__ = extend_path(__path__, __name__)
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This will add to the package's ``__path__`` all subdirectories of directories on
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``sys.path`` named after the package. This is useful if one wants to distribute
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different parts of a single logical package as multiple directories.
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This will add to the package's ``__path__`` all subdirectories of directories
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on ``sys.path`` named after the package. This is useful if one wants to
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distribute different parts of a single logical package as multiple
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directories.
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It also looks for :file:`\*.pkg` files beginning where ``*`` matches the *name*
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argument. This feature is similar to :file:`\*.pth` files (see the :mod:`site`
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module for more information), except that it doesn't special-case lines starting
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with ``import``. A :file:`\*.pkg` file is trusted at face value: apart from
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checking for duplicates, all entries found in a :file:`\*.pkg` file are added to
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the path, regardless of whether they exist on the filesystem. (This is a
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feature.)
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It also looks for :file:`\*.pkg` files beginning where ``*`` matches the
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*name* argument. This feature is similar to :file:`\*.pth` files (see the
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:mod:`site` module for more information), except that it doesn't special-case
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lines starting with ``import``. A :file:`\*.pkg` file is trusted at face
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value: apart from checking for duplicates, all entries found in a
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:file:`\*.pkg` file are added to the path, regardless of whether they exist
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on the filesystem. (This is a feature.)
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If the input path is not a list (as is the case for frozen packages) it is
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returned unchanged. The input path is not modified; an extended copy is
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returned. Items are only appended to the copy at the end.
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It is assumed that ``sys.path`` is a sequence. Items of ``sys.path`` that are
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not strings referring to existing directories are ignored. Unicode items on
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``sys.path`` that cause errors when used as filenames may cause this function
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to raise an exception (in line with :func:`os.path.isdir` behavior).
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It is assumed that :data:`sys.path` is a sequence. Items of :data:`sys.path`
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that are not strings referring to existing directories are ignored. Unicode
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items on :data:`sys.path` that cause errors when used as filenames may cause
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this function to raise an exception (in line with :func:`os.path.isdir`
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behavior).
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.. class:: ImpImporter(dirname=None)
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:pep:`302` Importer that wraps Python's "classic" import algorithm.
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If *dirname* is a string, a :pep:`302` importer is created that searches that
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directory. If *dirname* is ``None``, a :pep:`302` importer is created that
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searches the current :data:`sys.path`, plus any modules that are frozen or
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built-in.
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Note that :class:`ImpImporter` does not currently support being used by
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placement on :data:`sys.meta_path`.
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.. class:: ImpLoader(fullname, file, filename, etc)
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:pep:`302` Loader that wraps Python's "classic" import algorithm.
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.. function:: find_loader(fullname)
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Find a :pep:`302` "loader" object for *fullname*.
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If *fullname* contains dots, path must be the containing package's
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``__path__``. Returns ``None`` if the module cannot be found or imported.
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This function uses :func:`iter_importers`, and is thus subject to the same
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limitations regarding platform-specific special import locations such as the
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Windows registry.
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.. function:: get_importer(path_item)
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Retrieve a :pep:`302` importer for the given *path_item*.
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The returned importer is cached in :data:`sys.path_importer_cache` if it was
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newly created by a path hook.
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If there is no importer, a wrapper around the basic import machinery is
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returned. This wrapper is never inserted into the importer cache (None is
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inserted instead).
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The cache (or part of it) can be cleared manually if a rescan of
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:data:`sys.path_hooks` is necessary.
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.. function:: get_loader(module_or_name)
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Get a :pep:`302` "loader" object for *module_or_name*.
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If the module or package is accessible via the normal import mechanism, a
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wrapper around the relevant part of that machinery is returned. Returns
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``None`` if the module cannot be found or imported. If the named module is
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not already imported, its containing package (if any) is imported, in order
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to establish the package ``__path__``.
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This function uses :func:`iter_importers`, and is thus subject to the same
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limitations regarding platform-specific special import locations such as the
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Windows registry.
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.. function:: iter_importers(fullname='')
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Yield :pep:`302` importers for the given module name.
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If fullname contains a '.', the importers will be for the package containing
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fullname, otherwise they will be importers for :data:`sys.meta_path`,
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:data:`sys.path`, and Python's "classic" import machinery, in that order. If
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the named module is in a package, that package is imported as a side effect
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of invoking this function.
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Non-:pep:`302` mechanisms (e.g. the Windows registry) used by the standard
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import machinery to find files in alternative locations are partially
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supported, but are searched *after* :data:`sys.path`. Normally, these
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locations are searched *before* :data:`sys.path`, preventing :data:`sys.path`
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entries from shadowing them.
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For this to cause a visible difference in behaviour, there must be a module
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or package name that is accessible via both :data:`sys.path` and one of the
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non-:pep:`302` file system mechanisms. In this case, the emulation will find
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the former version, while the builtin import mechanism will find the latter.
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Items of the following types can be affected by this discrepancy:
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``imp.C_EXTENSION``, ``imp.PY_SOURCE``, ``imp.PY_COMPILED``,
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``imp.PKG_DIRECTORY``.
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.. function:: iter_modules(path=None, prefix='')
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Yields ``(module_loader, name, ispkg)`` for all submodules on *path*, or, if
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path is ``None``, all top-level modules on ``sys.path``.
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*path* should be either ``None`` or a list of paths to look for modules in.
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*prefix* is a string to output on the front of every module name on output.
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.. function:: walk_packages(path=None, prefix='', onerror=None)
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Yields ``(module_loader, name, ispkg)`` for all modules recursively on
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*path*, or, if path is ``None``, all accessible modules.
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*path* should be either ``None`` or a list of paths to look for modules in.
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*prefix* is a string to output on the front of every module name on output.
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Note that this function must import all *packages* (*not* all modules!) on
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the given *path*, in order to access the ``__path__`` attribute to find
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submodules.
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*onerror* is a function which gets called with one argument (the name of the
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package which was being imported) if any exception occurs while trying to
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import a package. If no *onerror* function is supplied, :exc:`ImportError`\s
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are caught and ignored, while all other exceptions are propagated,
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terminating the search.
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Examples::
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# list all modules python can access
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walk_packages()
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# list all submodules of ctypes
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walk_packages(ctypes.__path__, ctypes.__name__ + '.')
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.. function:: get_data(package, resource)
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Get a resource from a package.
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This is a wrapper for the :pep:`302` loader :func:`get_data` API. The package
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argument should be the name of a package, in standard module format
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(foo.bar). The resource argument should be in the form of a relative
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filename, using ``/`` as the path separator. The parent directory name
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This is a wrapper for the :pep:`302` loader :func:`get_data` API. The
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*package* argument should be the name of a package, in standard module format
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(``foo.bar``). The *resource* argument should be in the form of a relative
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filename, using ``/`` as the path separator. The parent directory name
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``..`` is not allowed, and nor is a rooted name (starting with a ``/``).
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The function returns a binary string that is the contents of the
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specified resource.
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The function returns a binary string that is the contents of the specified
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resource.
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For packages located in the filesystem, which have already been imported,
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this is the rough equivalent of::
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d = os.path.dirname(sys.modules[package].__file__)
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data = open(os.path.join(d, resource), 'rb').read()
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d = os.path.dirname(sys.modules[package].__file__)
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data = open(os.path.join(d, resource), 'rb').read()
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If the package cannot be located or loaded, or it uses a :pep:`302` loader
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which does not support :func:`get_data`, then None is returned.
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which does not support :func:`get_data`, then ``None`` is returned.
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