"""Open/Closed Principle
Example inspired by this wonderful piece here: http://joelabrahamsson.com/a-simple-example-of-the-openclosed-principle/
"""

# Area calculator: calculate area of a rectangle
class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height
    
    def area(self):
        return self.width * self.height

# Calculate area of multiple rectangles  
    
class AreaCalculator: