How to use the stevedore.enabled.EnabledExtensionManager function in stevedore

def _load_all_extensions(self):
        self.api_extension_manager = stevedore.enabled.EnabledExtensionManager(
            namespace=self.EXT_NAMESPACE,
            check_func=self._check_load_extension,
            invoke_on_load=True,
            invoke_kwds={})
        self.api_extension_manager.map(self.add_extension)

LOG.debug("Did not find any server create extensions")

        # Look for implementation of extension point of server rebuild
        self.rebuild_extension_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_REBUILD_NAMESPACE,
                check_func=_check_load_extension('server_rebuild'),
                invoke_on_load=True,
                invoke_kwds={"extension_info": self.extension_info},
                propagate_map_exceptions=True)
        if not list(self.rebuild_extension_manager):
            LOG.debug("Did not find any server rebuild extensions")

        # Look for implementation of extension point of server update
        self.update_extension_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_UPDATE_NAMESPACE,
                check_func=_check_load_extension('server_update'),
                invoke_on_load=True,
                invoke_kwds={"extension_info": self.extension_info},
                propagate_map_exceptions=True)
        if not list(self.update_extension_manager):
            LOG.debug("Did not find any server update extensions")

        # Look for implementation of extension point of server resize
        self.resize_extension_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_RESIZE_NAMESPACE,
                check_func=_check_load_extension('server_resize'),
                invoke_on_load=True,
                invoke_kwds={"extension_info": self.extension_info},
                propagate_map_exceptions=True)

LOG.debug(
                            'extension %(ext_alias)s is missing %(func)s',
                            {'ext_alias': ext.obj.alias,
                            'func': required_function})
                        return False
                else:
                    return False
            return check_load_extension

        self.extension_info = kwargs.pop('extension_info')
        super(ServersController, self).__init__(**kwargs)
        self.compute_api = compute.API(skip_policy_check=True)

        # Look for implementation of extension point of server creation
        self.create_extension_manager = \
          stevedore.enabled.EnabledExtensionManager(
              namespace=self.EXTENSION_CREATE_NAMESPACE,
              check_func=_check_load_extension('server_create'),
              invoke_on_load=True,
              invoke_kwds={"extension_info": self.extension_info},
              propagate_map_exceptions=True)
        if not list(self.create_extension_manager):
            LOG.debug("Did not find any server create extensions")

        # Look for implementation of extension point of server rebuild
        self.rebuild_extension_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_REBUILD_NAMESPACE,
                check_func=_check_load_extension('server_rebuild'),
                invoke_on_load=True,
                invoke_kwds={"extension_info": self.extension_info},
                propagate_map_exceptions=True)

self.update_schema_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_UPDATE_NAMESPACE,
                check_func=_check_load_extension('get_server_update_schema'),
                invoke_on_load=True,
                invoke_kwds={"extension_info": self.extension_info},
                propagate_map_exceptions=True)
        if list(self.update_schema_manager):
            self.update_schema_manager.map(self._update_extension_schema,
                                           self.schema_server_update)
        else:
            LOG.debug("Did not find any server update schemas")

        # Look for API schema of server rebuild extension
        self.rebuild_schema_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_REBUILD_NAMESPACE,
                check_func=_check_load_extension('get_server_rebuild_schema'),
                invoke_on_load=True,
                invoke_kwds={"extension_info": self.extension_info},
                propagate_map_exceptions=True)
        if list(self.rebuild_schema_manager):
            self.rebuild_schema_manager.map(self._rebuild_extension_schema,
                                            self.schema_server_rebuild)
        else:
            LOG.debug("Did not find any server rebuild schemas")

        # Look for API schema of server resize extension
        self.resize_schema_manager = \
            stevedore.enabled.EnabledExtensionManager(
                namespace=self.EXTENSION_RESIZE_NAMESPACE,
                check_func=_check_load_extension('get_server_resize_schema'),

def make_app():
    """App builder (wsgi).

    Entry point for Blazar REST API server.
    """
    app = flask.Flask('blazar.api')

    app.route('/', methods=['GET'])(version_list)
    app.route('/versions', methods=['GET'])(version_list)

    LOG.debug("List of plugins: %s", cfg.CONF.manager.plugins)

    plugins = cfg.CONF.manager.plugins + ['leases']
    extension_manager = enabled.EnabledExtensionManager(
        check_func=lambda ext: ext.name in plugins,
        namespace='blazar.api.v1.extensions',
        invoke_on_load=False
        )

    for ext in extension_manager.extensions:
        bp = ext.plugin()
        app.register_blueprint(bp, url_prefix=bp.url_prefix)

    for code in werkzeug_exceptions.default_exceptions:
        app.register_error_handler(code, make_json_error)

    if cfg.CONF.debug and not cfg.CONF.log_exchange:
        LOG.debug('Logging of request/response exchange could be enabled '
                  'using flag --log_exchange')