計算移動平均數

            :rtype: 序列 舊→新

def moving_average(self, data, days):
        """ 計算移動平均數

            :rtype: 序列 舊→新
        """
        result = []
        data = data[:]
        for dummy in range(len(data) - int(days) + 1):
            result.append(round(sum(data[-days:]) / days, 2))
            data.pop()
        result.reverse()
        return result