code: def close_pct_change(self):
          '返回DataStruct.close的百分比变化'
          res = self.close.groupby(level=1).apply(lambda x: x.pct_change())
          res.name = 'close_pct_change'
          return ref close_pct_change(self):
          '返回DataStruct.close的百分比变化'
          res = self.close.groupby(level=1).apply(lambda x: x.pct_change())
          res.name = 'close_pct_change'
          return res
docs: 返回DataStruct.close的百分比变化