Novaclient 载入 extensions 的过程

@utils.arg('server',
        metavar='<server>',
        help=_('Name or UUID of the server to list actions for.'))
def do_instance_action_list(cs, args):
    """List actions on a server."""
    server = utils.find_resource(cs.servers, args.server)
    actions = cs.instance_action.list(server)
    utils.print_list(actions,
        ['Action', 'Request_ID', 'Message', 'Start_Time'], sortby_index=3)

# build available subcommands based on version
self.extensions = self._discover_extensions(
        options.os_compute_api_version)

def _discover_extensions(self, version):
    extensions = []
    for name, module in itertools.chain(
            self._discover_via_python_path(),
            self._discover_via_contrib_path(version),
            self._discover_via_entry_points()):

        extension = novaclient.extension.Extension(name, module)
        extensions.append(extension)

    return extensions

def _discover_via_contrib_path(self, version):
    module_path = os.path.dirname(os.path.abspath(__file__))
    version_str = "v%s" % version.replace('.', '_')
    ext_path = os.path.join(module_path, version_str, 'contrib')
    ext_glob = os.path.join(ext_path, "*.py")

    for ext_path in glob.iglob(ext_glob):
        name = os.path.basename(ext_path)[:-3]

        if name == "__init__":
            continue

        module = imp.load_source(name, ext_path)

        yield name, module