Liskov Substitution Principle

Subtypes must be substitutable for their base type without breaking behavior.

# dirty — Square breaks Rectangle's contract
class Rectangle:
    def set_width(self, w):
        self.width = w
    def set_height(self, h):
        self.height = h
    def area(self):
        return self.width * self.height

class Square(Rectangle):
    def set_width(self, w):
        self.width = w
        self.height = w  # breaks LSP!
    def set_height(self, h):
        self.width = h
        self.height = h

Refactor using factory functions so create_rectangle and create_square are independent — no inheritance. Both expose an area callable.

solve('square', 5) → 25 (side²)
solve('rect', 4, 6) → 24 (width × height)