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Open/Closed Principle

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Dominic Yeboah
·

1 min read

Open/Closed Principle: Software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. Here is an example of a function that violates the Open/Closed Principle by requiring modification every time we want to add a new shape.


def shape(shape):
    if shape == 'circle':
        draw_circle()
    elif shape == 'square':
        draw_square()
    elif shape == 'triangle':
        draw_triangle()
    else:
        raise Exception('Unknown shape')


To adhere to the Open/Closed Principle, we can use inheritance and
polymorphism to extend the functionality of the area function without modifying it:


class Shape:
    def area(self):
        pass

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return 3.14 * self.radius * self.radius

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

    def area(self):
        return self.side * self.side

def calculate_area(shape):
    return shape.area()
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