Example of using `__new__` as a subclass factory

new_factory.py

class Number:
    def __new__(cls, literal):
        for scls in cls.__subclasses__():
            try:
                return scls(literal)
            except (TypeError, ValueError):
                pass
        raise TypeError("The path to hell is paved with incomplete examples")
    
    # here be numerical operations!


class Integer(Number):
    def __new__(cls, literal):
        value = int(literal)
        self = object.__new__(Integer)
        self._value = value
        return self

    def __repr__(self):
        return str(self._value)


class Fraction(Number):
    def __new__(cls, literal):
        numerator, denominator = map(int, literal.split('/'))
        self = object.__new__(Fraction)
        self._numerator, self._denominator = numerator, denominator
        return self

    def __repr__(self):
        return f"{self._numerator} / {self._denominator}"


print(Number('12'))
print(Number('12/5'))