code: def choose_location_ids(gtfs, stop_ids=None):
      
  
      if not stop_ids:
          # Select locations that are involved in pathway graph.
          return [location.gtfs_id
                  for location in gtfs.locations
                  if location.station().self_or_children_have_pathways()]
  
      station_ids = set()
      try:
          for stop_id in stop_ids.split(','):
              station = gtfs.get_location(stop_id).station()
              station_ids.add(station.gtfs_id)
              print('Visualizing station %s' % station.gtfs_id)
      except KeyError:
          raise Exception('Cannot find location with stop_id=%s' % stop_id)
  
      location_ids = station_ids.copy()
      for station_id in station_ids:
          for child_id in gtfs.get_location(station_id).children:
              # Child is a platform, entrance or generic node.
              location_ids.add(child_id)
              # Add boarding areas if they are present for this child platform.
              for boarding_area_id in gtfs.get_location(child_id).children:
                  location_ids.add(gtfs.get_location(boarding_area_id).gtfs_id)
  
      return location_ids
docs: Chooses a set of location ids (stations and their children) for
      rendering a pathway graph.
  
      If stop_ids is None, then all stations that have pathways are chosen.
  
      If stop_ids is not None, then the station with this stop_id (or
      with a child with this stop_id) is chosen.