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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() |