code: def form_uri(item_id, service, is_track):
      
      if is_track:
          uri = service.sonos_uri_from_id(item_id)
      else:
          uri = 'x-rincon-cpcontainer:' + item_id
      return uri
docs: Form and return a music service item uri
  
      Args:
          item_id (str): The item id
          service (MusicService): The music service that the item originates from
          is_track (bool): Whether the item_id is from a track or not
  
      Returns:
          str: The music service item uri