code: def op_music_to_playlist(self, mid, pid, op):
          
          url_add = uri + '/playlist/manipulate/tracks'
          trackIds = '["' + str(mid) + '"]'
          data_add = {
              'tracks': str(mid),  # music id
              'pid': str(pid),    # playlist id
              'trackIds': trackIds,  # music id str
              'op': op   # opation
          }
          data = self.request('POST', url_add, data_add)
          code = data.get('code')
  
          # 从歌单中成功的移除歌曲时，code 是 200
          # 当从歌单中移除一首不存在的歌曲时，code 也是 200
          # 当向歌单添加歌曲时，如果歌曲已经在列表当中，
          # 返回 code 为 502
          if code == 200:
              return 1
          elif code == 502:
              return -1
          else:
              return 0
docs: :param op: add or del