用python写一个程序，定义有理数类，并创建两个实例，从键盘输入有理数，完成有理数的相加、相乘

当然可以，下面是一个简单的Python程序示例，用于定义一个有理数类(Rational)，并实现了相加和相乘的功能：

class Rational:
    def __init__(self, numerator, denominator):
        self.numerator = numerator
        self.denominator = abs(denominator)

    # 定义相加函数
    def add(self, other):
        new_numerator = self.numerator * other.denominator + other.numerator * self.denominator
        new_denominator = self.denominator * other.denominator
        return Rational(new_numerator, new_denominator)

    # 定义相乘函数
    def multiply(self, other):
        new_numerator = self.numerator * other.numerator
        new_denominator = self.denominator * other.denominator
        return Rational(new_numerator, new_denominator)

# 创建两个Rational实例
num1 = input("请输入第一个有理数的分子 (numerator): ")
den1 = input("请输入第一个有理数的分母 (denominator, 非零): ")
num1 = int(num1)
den1 = int(den1)

num2 = input("请输入第二个有理数的分子 (numerator): ")
den2 = input("请输入第二个有理数的分母 (denominator, 非零): ")
num2 = int(num2)
den2 = int(den2)

# 确保分母不为0
if den1 == 0 or den2 == 0:
    print("分母不能为0")
else:
    num1_rational = Rational(num1, den1)
    num2_rational = Rational(num2, den2)

    # 相加
    sum_result = num1_rational.add(num2_rational)
    print(f"两数相加的结果为: {sum_result.numerator}/{sum_result.denominator}")

    # 相乘
    product_result = num1_rational.multiply(num2_rational)
    print(f"两数相乘的结果为: {product_result.numerator}/{product_result.denominator}")

运行此程序后，用户将被提示输入两个有理数的分子和分母。然后程序会计算它们的和与积。