How to use the scenario.FetchMessagesScenario function in scenario

def fetch_messages(self, messages=None):
        if messages is None:
            messages = self.messages

        if len(messages) == 0:
            return

        fm = scenario.FetchMessagesScenario(self._rsi,
                 (self.__fetch_message_cb,),
                 (self.__common_errback,),
                 (self.__fetch_messages_cb, messages))
        fm.message_ids = [m.id for m in messages]
        fm()

def fetch_messages(self, messages=None):
        if messages is None:
            messages = self.messages

        if len(messages) == 0:
            return

        fm = scenario.FetchMessagesScenario(self._rsi,
                 (self.__fetch_message_cb,),
                 (self.__common_errback,),
                 (self.__fetch_messages_cb, messages))
        fm.message_ids = [m.id for m in messages]
        fm()

def fetch_messages(self, messages=None):
        if messages is None:
            messages = self.messages

        if len(messages) == 0:
            return

        fm = scenario.FetchMessagesScenario(self._rsi,
                 (self.__fetch_message_cb,),
                 (self.__common_errback,),
                 (self.__fetch_messages_cb, messages))
        fm.message_ids = [m.id for m in messages]
        fm()