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"""

*What is this pattern about?

The composite pattern describes a group of objects that is treated the

same way as a single instance of the same type of object. The intent of

a composite is to "compose" objects into tree structures to represent

part-whole hierarchies. Implementing the composite pattern lets clients

treat individual objects and compositions uniformly.

*What does this example do?

The example implements a graphic class，which can be either an ellipse

or a composition of several graphics. Every graphic can be printed.

*Where is the pattern used practically?

In graphics editors a shape can be basic or complex. An example of a

simple shape is a line, where a complex shape is a rectangle which is

made of four line objects. Since shapes have many operations in common

such as rendering the shape to screen, and since shapes follow a

part-whole hierarchy, composite pattern can be used to enable the

program to deal with all shapes uniformly.

*References:

https://en.wikipedia.org/wiki/Composite_pattern

https://infinitescript.com/2014/10/the-23-gang-of-three-design-patterns/

*TL;DR

Describes a group of objects that is treated as a single instance.

"""

from abc import ABC, abstractmethod

from typing import List

class Graphic(ABC):

@abstractmethod

def render(self) -> None:

raise NotImplementedError("You should implement this!")

class CompositeGraphic(Graphic):

def __init__(self) -> None:

self.graphics: List[Graphic] = []

def render(self) -> None:

for graphic in self.graphics:

graphic.render()

def add(self, graphic: Graphic) -> None:

self.graphics.append(graphic)

def remove(self, graphic: Graphic) -> None:

self.graphics.remove(graphic)

class Ellipse(Graphic):

def __init__(self, name: str) -> None:

self.name = name

def render(self) -> None:

print(f"Ellipse: {self.name}")

def main():

"""

>>> ellipse1 = Ellipse("1")

>>> ellipse2 = Ellipse("2")

>>> ellipse3 = Ellipse("3")

>>> ellipse4 = Ellipse("4")

>>> graphic1 = CompositeGraphic()

>>> graphic2 = CompositeGraphic()

>>> graphic1.add(ellipse1)

>>> graphic1.add(ellipse2)

>>> graphic1.add(ellipse3)

>>> graphic2.add(ellipse4)

>>> graphic = CompositeGraphic()

>>> graphic.add(graphic1)

>>> graphic.add(graphic2)

>>> graphic.render()

Ellipse: 1

Ellipse: 2

Ellipse: 3

Ellipse: 4

"""

if __name__ == "__main__":

import doctest

doctest.testmod()