composite.py

"""
*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()