code: def AddTrip(self, schedule=None, headsign=None, service_period=None,
                trip_id=None):
      
      if schedule is None:
        assert self._schedule is not None
        schedule = self._schedule
      if trip_id is None:
        trip_id = util.FindUniqueId(schedule.trips)
      if service_period is None:
        service_period = schedule.GetDefaultServicePeriod()
      trip_class = self.GetGtfsFactory().Trip
      trip_obj = trip_class(route=self, headsign=headsign,
                  service_period=service_period, trip_id=trip_id)
      schedule.AddTripObject(trip_obj)
      return trip_obj
docs: Add a trip to this route.
  
      Args:
        schedule: a Schedule object which will hold the new trip or None to use
          the schedule of this route.
        headsign: headsign of the trip as a string
        service_period: a ServicePeriod object or None to use
          schedule.GetDefaultServicePeriod()
        trip_id: optional trip_id for the new trip
  
      Returns:
        a new Trip object