def __directory_list_descriptor(self, configs):
descriptor = {<EOL>'<STR_LIT>': '<STR_LIT>',<EOL>'<STR_LIT>': '<STR_LIT>',<EOL>}<EOL>items = []<EOL>for config in configs:<EOL><INDENT>item_descriptor = self.__item_descriptor(config)<EOL>if item_descriptor:<EOL><INDENT>items.append(item_descriptor)<EOL><DEDENT><DEDENT>if items:<EOL><INDENT>descriptor['<STR_LIT>'] = items<EOL><DEDENT>return descriptor<EOL>
Builds a directory list for an API.

        Args:
          configs: List of dicts containing the service configurations to list.

        Returns:
          A dictionary that can be deserialized into JSON in discovery list format.

        Raises:
          ApiConfigurationError: If there's something wrong with the API
            configuration, such as a multiclass API decorated with different API
            descriptors (see the docstring for api()), or a repeated method
            signature.