The special method __repr__ gives us the ability to define the way the object is represented in a Python interpreter. For rational numbers, a possible definition of this method could be as follows:

class RationalNumber:
    ...
    def __repr__(self): 
        return f'{self.numerator} / {self.denominator}'

With this method defined, just typing q returns 10 / 20.

We would like to have a method that performs the addition of two rational numbers. A first attempt could result in a method like this:

class RationalNumber:
    ...
    def add(self, other): 
        p1, q1 = self.numerator, self.denominator 
        if isinstance(other, int):        
            p2, q2 = other, 1 
        else: 
            p2, q2 = other.numerator, other.denominator 
        return RationalNumber(p1 * q2 + p2 * q1, q1 * q2)

A call to this method takes the following form:

q = RationalNumber(1, 2)
p = RationalNumber(1, 3)
q.add(p)   # returns the RationalNumber for 5/6

It would be much...