Adapter

An adapter is a construct whcih adapts an existing interface to conform to another required interface. This could be a factory which takes one object and transforms it into another, or it can be a wrapper around the object that performs the operations on the fly.

from unittest import TestCase

class Square:
    def __init__(self, side=0):
        self.side = side

def calculate_area(rc):
    return rc.width * rc.height

class SquareToRectangleAdapter:
    def __init__(self, square):
        self.square = square

    @property
    def width(self):
        return self.square.side

    @property
    def height(self):
        return self.square.side

class Evaluate(TestCase):
    def test_exercise(self):
        sq = Square(11)
        adapter = SquareToRectangleAdapter(sq)
        self.assertEqual(121, calculate_area(adapter))
        sq.side = 10
        self.assertEqual(100, calculate_area(adapter))