
"pkgutil" --- Package extension utility
***************************************

**Source code:** Lib/pkgutil.py

======================================================================

This module provides utilities for the import system, in particular
package support.

pkgutil.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
   "__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 "*.pkg" files beginning where "*" matches the
   *name* argument.  This feature is similar to "*.pth" files (see the
   "site" module for more information), except that it doesn't
   special-case lines starting with "import".  A "*.pkg" file is
   trusted at face value: apart from checking for duplicates, all
   entries found in a "*.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 "sys.path" is a sequence.  Items of "sys.path"
   that are not strings referring to existing directories are ignored.
   Unicode items on "sys.path" that cause errors when used as
   filenames may cause this function to raise an exception (in line
   with "os.path.isdir()" behavior).

class class pkgutil.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 "sys.path", plus any
   modules that are frozen or built-in.

   Note that "ImpImporter" does not currently support being used by
   placement on "sys.meta_path".

   Deprecated since version 3.3: This emulation is no longer needed,
   as the standard import mechanism is now fully PEP 302 compliant and
   available in "importlib".

class class pkgutil.ImpLoader(fullname, file, filename, etc)

   **PEP 302** Loader that wraps Python's "classic" import algorithm.

   Deprecated since version 3.3: This emulation is no longer needed,
   as the standard import mechanism is now fully PEP 302 compliant and
   available in "importlib".

pkgutil.find_loader(fullname)

   Retrieve a **PEP 302** module loader for the given *fullname*.

   This is a backwards compatibility wrapper around
   "importlib.util.find_spec()" that converts most failures to
   "ImportError" and only returns the loader rather than the full
   "ModuleSpec".

   Changed in version 3.3: Updated to be based directly on "importlib"
   rather than relying on the package internal PEP 302 import
   emulation.

   Changed in version 3.4: Updated to be based on **PEP 451**

pkgutil.get_importer(path_item)

   Retrieve a **PEP 302** importer for the given *path_item*.

   The returned importer is cached in "sys.path_importer_cache" if it
   was newly created by a path hook.

   The cache (or part of it) can be cleared manually if a rescan of
   "sys.path_hooks" is necessary.

   Changed in version 3.3: Updated to be based directly on "importlib"
   rather than relying on the package internal PEP 302 import
   emulation.

pkgutil.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__".

   Changed in version 3.3: Updated to be based directly on "importlib"
   rather than relying on the package internal PEP 302 import
   emulation.

   Changed in version 3.4: Updated to be based on **PEP 451**

pkgutil.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 all registered top
   level importers (i.e. those on both sys.meta_path and
   sys.path_hooks).

   If the named module is in a package, that package is imported as a
   side effect of invoking this function.

   If no module name is specified, all top level importers are
   produced.

   Changed in version 3.3: Updated to be based directly on "importlib"
   rather than relying on the package internal PEP 302 import
   emulation.

pkgutil.iter_modules(path=None, prefix='')

   Yields "(module_finder, 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 a *finder* which defines an "iter_modules()"
     method. This interface is non-standard, so the module also
     provides implementations for "importlib.machinery.FileFinder" and
     "zipimport.zipimporter".

   Changed in version 3.3: Updated to be based directly on "importlib"
   rather than relying on the package internal PEP 302 import
   emulation.

pkgutil.walk_packages(path=None, prefix='', onerror=None)

   Yields "(module_finder, 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, "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 a *finder* which defines an "iter_modules()"
     method. This interface is non-standard, so the module also
     provides implementations for "importlib.machinery.FileFinder" and
     "zipimport.zipimporter".

   Changed in version 3.3: Updated to be based directly on "importlib"
   rather than relying on the package internal PEP 302 import
   emulation.

pkgutil.get_data(package, resource)

   Get a resource from a package.

   This is a wrapper for the **PEP 302** loader "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 "get_data()", then "None" is
   returned.
