Full code.

example_04.py

import math


class Square:
    length: int

    def __init__(self, length=0):
        self.length = length


class Circle:
    radius: int

    def __init__(self, radius=0):
        self.radius = radius


def area(any_object):
    if isinstance(any_object, Circle):
        return math.pi * (math.pow(any_object.radius, 2))

    elif isinstance(any_object, Square):
        return (math.pow(any_object.length, 2))


my_circle = Circle(6)
my_square = Square(12)

print(area(my_circle))
print(area(my_square))