code: def bar_amplitude(self):
          "返回bar振幅"
          res = (self.high - self.low) / self.low
          res.name = 'bar_amplitude'
          return ref bar_amplitude(self):
          "返回bar振幅"
          res = (self.high - self.low) / self.low
          res.name = 'bar_amplitude'
          return res
docs: 返回bar振幅