code: def bar_pct_change(self):
          '返回bar的涨跌幅'
          res = (self.close - self.open) / self.open
          res.name = 'bar_pct_change'
          return ref bar_pct_change(self):
          '返回bar的涨跌幅'
          res = (self.close - self.open) / self.open
          res.name = 'bar_pct_change'
          return res
docs: 返回bar的涨跌幅