<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def stop_sequence(self):
 """Return the sorted StopTimes for this trip."""

    return sorted(
      self.stop_times(),
      key=lambda x:int(x.get('stop_sequence'))
    )