of
PEP 302 support, and setuptools, among other things.

At the top, you have "PythonPath", an abstract representation of sys.path which
includes methods to locate top-level modules, with or without loading them.
The top-level exposed functions in this module for accessing the system path
are "walkModules", "iterModules", and "getModule".

From most to least specific, here are the objects provided::

                  PythonPath  # sys.path
                      |
                      v
                  PathEntry   # one entry on sys.path: an importer
                      |
                      v
                 PythonModule # a module or package that can be loaded
                      |
                      v
                 PythonAttribute # an attribute of a module (function or class)
                      |
                      v
                 PythonAttribute # an attribute of a function or class
                      |
                      v
                     ...

Here's an example of idiomatic usage: this is what you would do to list all of
the modules outside the standard library's python-files directory::

    import os
    stdlibdir = os.path.dirname(os.__file__)

    from twisted.python.modules import iterModules

    for modinfo in iterModules():
        if (modinfo.pathEntry.filePath.path != stdlibdir
            and not modinfo.isPackage()):
            print('unpackaged: %s: %s' % (
                modinfo.name, modinfo.filePath.path))

@var theSystemPath: The very top of the Python object space.
@type: L{PythonPath}
é