Abstracts, Interfaces, Class, Python.
self.radius * self.radius def perimeter(self): return 2 * 3.14 * self.radius class Square(Shape): def __init__(self, side_length): self.side_length = side_length def area(self): return self.side_length * self.side_length def perimeter(self): return 4 * self.side_length # Usage circle = Circle(5)