SOLID - Open/Closed

o.py

class Calculator:

    def __init__(self, a, b):
        self._a = a
        self._b = b
        pass

    def calculate(self, operation):

        if operation == "sum":
            return self._a + self._b
        elif operation == "sub":
            return self._a - self._b
        elif operation == "mult":
            return self._a * self._b
        elif operation == "div":
            return self._a / self._b
        elif operation == "pow":
            return self._a / self._b
        elif operation == "rest":
            return self._a % self._b
        else:
            raise ValueError("Operation not found")


def main(a, b, operation):

    c = Calculator(a, b)
    print(c.calculate(operation))
    pass


main(5, 6, "sum")