code: def on_song_changed(self, song):
          
          if song is None or song.lyric is None:
              self._lyric = None
              self._pos_s_map = {}
          else:
              self._lyric = song.lyric.content
              self._pos_s_map = parse(self._lyric)
          self._pos_list = sorted(list(self._pos_s_map.keys()))
          self._pos = None
          self.current_sentence = ''
docs: bind song changed signal with this