返回当前播放歌曲歌词

def get_lrc(self):
        """
        返回当前播放歌曲歌词
        """
        if self._playingsong != self._pre_playingsong:
            self._lrc = douban.get_lrc(self._playingsong)
            self._pre_playingsong = self._playingsong
        return self._lrc