Composite Design Pattern in Python....

When I first started studying the Gang of Four book back in 2003-2004, it was an absolutely new thing to me. I must admit today that not everything became clear at that time. But gradually, the knowledge is being imbibed, and now while teaching my young son Ridit on this subject, I just love it.

Moreover, as I am now comfortable with three languages namely C++, Java, and Python, recreating the stuff for various languages looks pretty easy now.

So, today, I am rewriting the Composite Design Pattern in Python. Here goes my original Composite Design pattern implemented using C++ and written in 2008.

And here goes the exploration of the Composite Design Pattern by my young son, Ridit, currently a class VII student.

And here goes the Composite Design Pattern implemented in Python.

I hope you will like it.

from abc import ABC, abstractmethod

class Shape(ABC):
    def __init__(self):
        self.parent = None

    @abstractmethod
    def add(self, shape):
        pass

    @abstractmethod
    def remove(self, shape):
        pass

    def get_parent(self):
        return self.parent

    def set_parent(self, parent):
        self.parent = parent

    @abstractmethod
    def display(self):
        pass

class CompositeShape(Shape):
    def __init__(self):
        super().__init__()
        self.list_of_shapes = []

    def add(self, shape):
        shape.set_parent(self)
        self.list_of_shapes.append(shape)

    def remove(self, shape):
        self.list_of_shapes.remove(shape)
        shape.set_parent(None)

    def display(self):
        pass

class Point(Shape):
    def __init__(self, x, y):
        super().__init__()
        self.x = x
        self.y = y

    def display(self):
        print("X =", self.x, "Y =", self.y)

    def add(self, shape):
        print("This is a leaf class.... Can't add to it...")

    def remove(self, shape):
        print("This is a leaf class.... Can't remove from it...")

class Line(CompositeShape):
    def __init__(self, p1, p2):
        super().__init__()
        self.add(p1)
        self.add(p2)

    def display(self):
        print("The starting and end points of the line are")
        for shape in self.list_of_shapes:
            shape.display()

class Quadrilateral(CompositeShape):
    def __init__(self, p1, p2, p3, p4):
        super().__init__()
        self.add(p1)
        self.add(p2)
        self.add(p3)
        self.add(p4)

    def display(self):
        print("The four corners of the quadrilateral are")
        for shape in self.list_of_shapes:
            shape.display()

# Press the green button in the gutter to run the script.
if __name__ == '__main__':
    p1 = Point(10, 20)
    p2 = Point(30, 40)
    p3 = Point(50, 60)
    p4 = Point(70, 80)

    p1.add(p2)

    L1 = Line(p1, p2)
    q1 = Quadrilateral(p1, p2, p3, p4)

    p1.display()
    p2.display()
    L1.display()
    q1.display()

If we execute the above code, the console window will display the following result

This is a leaf class... Can't add to it...

X = 10 Y = 20

X = 30 Y = 40

The starting and end points of the line are

X = 10 Y = 20

X = 30 Y = 40

The four corners of the quadrilateral are

X = 10 Y = 20

X = 30 Y = 40

X = 50 Y = 60

X = 70 Y = 80