docs: def ladders(session, game_id):
      """Get a list of ladder IDs."""
      if isinstance(game_id, str):
          game_id = lookup_game_id(game_id)
      lobbies = get_lobbies(session, game_id)
      ladder_ids = set()
      for lobby in lobbies:
          ladder_ids |= set(lobby['ladders'])
      return list(ladder_ids)