code: def get_stops_for_route_type(self, route_type):
          
          if route_type is WALK:
              return self.stops()
          else:
              return pd.read_sql_query("SELECT DISTINCT stops.* "
                                       "FROM stops JOIN stop_times ON stops.stop_I == stop_times.stop_I "
                                       "           JOIN trips ON stop_times.trip_I = trips.trip_I"
                                       "           JOIN routes ON trips.route_I == routes.route_I "
                                       "WHERE routes.type=(?)", self.conn, params=(route_type,))
docs: Parameters
          ----------
          route_type: int
  
          Returns
          -------
          stops: pandas.DataFrame