def _shutdown_handler(self, event):  # pylint: disable=unused-argument
        """Listen shutdown event from kytos.

        This method listens the kytos/core.shutdown event and call the shutdown
        method from napp subclass implementation.

        Paramters
            event (:class:`KytosEvent`): event to be listened.
        """
        if not self.__event.is_set():
            self.__event.set()
            self.shutdown()