code: def fav_songs(self):
          
          if self._fav_songs is None:
              songs_data = self._api.user_favorite_songs(self.identifier)
              self._fav_songs = []
              if not songs_data:
                  return
              for song_data in songs_data:
                  song = _deserialize(song_data, NestedSongSchema)
                  self._fav_songs.append(song)
          return self._fav_songs
docs: FIXME: 支持获取所有的收藏歌曲