code: def get_walk_network(gtfs, max_link_distance_m=1000):
      
      assert (isinstance(gtfs, GTFS))
      return walk_transfer_stop_to_stop_network(gtfs, max_link_distance=max_link_distance_m)
docs: Parameters
      ----------
      gtfs: gtfspy.GTFS
  
      Returns
      -------
      walk_network: networkx.Graph: