《python语言程序设计》2018版第8章20题使用Rational类编写一个程序(上)-修改一下8-4Rational类我认为的错误

首先抄一下Rational类,可以安静的抄一遍

书中214-215页间程序清单8-4的代码如下:

class Rational:
    def __init__(self, numerator=1, denominator=0):
        divisor = gcd(numerator, denominator)
        self.__numerator = (1 if denominator > 0 else -1) * int(numerator / divisor)
        self.__denominator = int(abs(denominator) / divisor)

    def __add__(self, second_rational):
        n = self.__numerator * second_rational[1] + self.__denominator * second_rational[0]
        d = self.__denominator * second_rational[1]
        return Rational(n, d)

    def __sub__(self, second_rational):
        n = self.__numerator * second_rational[1] - self.__denominator * second_rational[0]
        d