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

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

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

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

class pkgutil.ModuleInfo(module_finder, name, ispkg)

   A namedtuple that holds a brief summary of a module's info.

   Added in version 3.6.

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__)

   For each directory on "sys.path" that has a subdirectory that
   matches the package name, add the subdirectory to the package's
   "__path__". 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 skipping blank lines and ignoring
   comments, 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).

pkgutil.get_importer(path_item)

   Retrieve a *finder* for the given *path_item*.

   The returned finder 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.iter_importers(fullname='')

   Yield *finder* objects for the given module name.

   If *fullname* contains a "'.'", the finders will be for the package
   containing *fullname*, otherwise they will be all registered top
   level finders (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 finders 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 "ModuleInfo" 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 "ModuleInfo" 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 *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 *loader*
   which does not support "get_data", then "None" is returned.  In
   particular, the *loader* for *namespace packages* does not support
   "get_data".

pkgutil.resolve_name(name)

   Resolve a name to an object.

   This functionality is used in numerous places in the standard
   library (see bpo-12915) - and equivalent functionality is also in
   widely used third-party packages such as setuptools, Django and
   Pyramid.

   It is expected that *name* will be a string in one of the following
   formats, where W is shorthand for a valid Python identifier and dot
   stands for a literal period in these pseudo-regexes:

   * "W(.W)*"

   * "W(.W)*:(W(.W)*)?"

   The first form is intended for backward compatibility only. It
   assumes that some part of the dotted name is a package, and the
   rest is an object somewhere within that package, possibly nested
   inside other objects. Because the place where the package stops and
   the object hierarchy starts can't be inferred by inspection,
   repeated attempts to import must be done with this form.

   In the second form, the caller makes the division point clear
   through the provision of a single colon: the dotted name to the
   left of the colon is a package to be imported, and the dotted name
   to the right is the object hierarchy within that package. Only one
   import is needed in this form. If it ends with the colon, then a
   module object is returned.

   The function will return an object (which might be a module), or
   raise one of the following exceptions:

   "ValueError" -- if *name* isn't in a recognised format.

   "ImportError" -- if an import failed when it shouldn't have.

   "AttributeError" -- If a failure occurred when traversing the
   object hierarchy within the imported package to get to the desired
   object.

   Added in version 3.9.
