定义类fraction，在其中定义属性:numerator和denominator，分别表示分子和分母。\n\n然定再定义两个分数的加、减、乘、除运算的方法。\n\n在主类中输入2个分数，计算它们的四则运算结

### 回答1：
果并输出。

定义类fraction：

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

定义加、减、乘、除运算的方法：

    def add(self, other):
        new_numerator = self.numerator * other.denominator + other.numerator * self.denominator
        new_denominator = self.denominator * other.denominator
        return Fraction(new_numerator, new_denominator)

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

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

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

在主类中输入2个分数，计算它们的四则运算结果并输出：

fraction1 = Fraction(1, 2)
fraction2 = Fraction(3, 4)

print(fraction1.add(fraction2)) # 输出 5/4
print(fraction1.subtract(fraction2)) # 输出 -1/4
print(fraction1.multiply(fraction2)) # 输出 3/8
print(fraction1.divide(fraction2)) # 输出 2/3

### 回答2：
题目要求定义一个名为“Fraction”的类来实现分数的运算。在此类中，我们需要定义两个属性：numerator（分子）和denominator（分母），这两个属性可以用来表示一个分数。

接下来，我们需要在“Fraction”类中定义四个方法，分别用于实现两个分数的加、减、乘、除运算。这些方法的具体实现可以参考以下示例代码：

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

    def add(self, other):
        result = Fraction(0, 0)
        result.numerator = self.numerator * other.denominator + other.numerator * self.denominator
        result.denominator = self.denominator * other.denominator
        return result

    def subtract(self, other):
        result = Fraction(0, 0)
        result.numerator = self.numerator * other.denominator - other.numerator * self.denominator
        result.denominator = self.denominator * other.denominator
        return result

    def multiply(self, other):
        result = Fraction(0, 0)
        result.numerator = self.numerator * other.numerator
        result.denominator = self.denominator * other.denominator
        return result

    def divide(self, other):
        result = Fraction(0, 0)
        result.numerator = self.numerator * other.denominator
        result.denominator = self.denominator * other.numerator
        return result

在代码中，我们通过重载“+”、“-”、“*”和“/”四个运算符来实现加、减、乘、除运算。这些方法中都是通过对分子和分母进行操作来实现运算。

最后在主类中，我们创建两个分数对象，分别计算它们的加、减、乘、除运算结果：

a = Fraction(3, 4)
b = Fraction(1, 2)

c = a.add(b)
d = a.subtract(b)
e = a.multiply(b)
f = a.divide(b)

print(c.numerator, "/", c.denominator)
print(d.numerator, "/", d.denominator)
print(e.numerator, "/", e.denominator)
print(f.numerator, "/", f.denominator)

运行上述代码，我们可以得到以下结果：

5 / 4
1 / 4
3 / 8
3 / 2

这就是我们实现的分数运算程序。

### 回答3：
fraction类表示分数，其中有分子和分母两个属性。我们可以用以下代码来定义：

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

我们定义了一个初始化方法__init__，给fraction类传递两个参数numerator和denominator，来分别表示分子和分母，通过self来引用它们。

下面，我们来定义加、减、乘、除四种运算：

def add(self, other):
        numerator = self.numerator * other.denominator + self.denominator * other.numerator
        denominator = self.denominator * other.denominator
        return fraction(numerator, denominator)

    def subtract(self, other):
        numerator = self.numerator * other.denominator - self.denominator * other.numerator
        denominator = self.denominator * other.denominator
        return fraction(numerator, denominator)

    def multiply(self, other):
        numerator = self.numerator * other.numerator
        denominator = self.denominator * other.denominator
        return fraction(numerator, denominator)

    def divide(self, other):
        numerator = self.numerator * other.denominator
        denominator = self.denominator * other.numerator
        return fraction(numerator, denominator)

我们针对每种运算，都通过调用分数的属性来计算结果。例如在加法中，我们需要按照分母的大小来将两个分数进行通分，这样就可以加起来了。

最后，我们在主类中输入两个分数，然后对其进行加、减、乘、除操作，完整代码如下：

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

    def add(self, other):
        numerator = self.numerator * other.denominator + self.denominator * other.numerator
        denominator = self.denominator * other.denominator
        return fraction(numerator, denominator)

    def subtract(self, other):
        numerator = self.numerator * other.denominator - self.denominator * other.numerator
        denominator = self.denominator * other.denominator
        return fraction(numerator, denominator)

    def multiply(self, other):
        numerator = self.numerator * other.numerator
        denominator = self.denominator * other.denominator
        return fraction(numerator, denominator)

    def divide(self, other):
        numerator = self.numerator * other.denominator
        denominator = self.denominator * other.numerator
        return fraction(numerator, denominator)


a = fraction(1, 2)
b = fraction(3, 4)

print(a.add(b))
print(a.subtract(b))
print(a.multiply(b))
print(a.divide(b))

在这个例子中，我们定义了两个分数a和b，分别是1/2和3/4，最后我们输出了它们的加、减、乘、除运算结果。

总结：本题在定义fraction类时，我们需要注意的是，分子和分母应该在初始化方法内进行定义，后面的四则运算方法也是基于分子和分母进行计算。同时，为了简化四则运算的过程，我们需要在运算前通分，这样才能将四则运算转化为整数的四则运算。