设计并实现一个减法和乘法分数计算器，输入分数形式a/b其中a，b为整数，计算结果也是a/b的表现形式

设计一个简单的分数计算器，我们可以先定义一个`Fraction`类，用于表示分数，包含两个私有属性`numerator`（分子）和`denominator`（分母）。然后提供加、减、乘、除的方法来进行运算。为了保持分数的形式，即结果始终为最简形式，我们还需要在运算结束后检查并简化分数。

class Fraction:
    def __init__(self, numerator, denominator):
        self.numerator = numerator
        self.denominator = abs(denominator)
        
    def simplify(self):
        gcd = self.gcd(self.numerator, self.denominator)
        self.numerator //= gcd
        self.denominator //= gcd
    
    def gcd(self, a, b):
        while b != 0:
            a, b = b, a % b
        return a
    
    def add(self, other):
        new_numerator = self.numerator * other.denominator + self.denominator * other.numerator
        new_denominator = self.denominator * other.denominator
        result = Fraction(new_numerator, new_denominator)
        result.simplify()
        return result

    def subtract(self, other):
        new_numerator = self.numerator * other.denominator - self.denominator * other.numerator
        new_denominator = self.denominator * other.denominator
        result = Fraction(new_numerator, new_denominator)
        result.simplify()
        return result

    def multiply(self, other):
        new_numerator = self.numerator * other.numerator
        new_denominator = self.denominator * other.denominator
        result = Fraction(new_numerator, new_denominator)
        result.simplify()
        return result

    def divide(self, other):
        if other.denominator == 0:
            raise ZeroDivisionError("Cannot divide by zero")
        new_numerator = self.numerator * other.denominator
        new_denominator = self.denominator * other.numerator
        result = Fraction(new_numerator, new_denominator)
        result.simplify()
        return result

# 使用示例
f1 = Fraction(4, 6)
f2 = Fraction(3, 5)

print(f1.add(f2))  # 输出: Fraction(19, 30) (已简化)

在这个例子中，用户可以创建`Fraction`对象，然后调用相应的`add`, `subtract`, `multiply`, 或 `divide` 方法来进行运算，并自动将结果保持在最简形式。