Python-Design-Patterns composite
composite Model
Python-Design-Patterns composite
# file: 'composite.py'
#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
*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;DR80
Describes a group of objects that is treated as a single instance.
"""
class Graphic:
def render(self):
raise NotImplementedError("You should implement this.")
class CompositeGraphic(Graphic):
def __init__(self):
self.graphics = []
def render(self):
for graphic in self.graphics:
graphic.render()
def add(self, graphic):
self.graphics.append(graphic)
def remove(self, graphic):
self.graphics.remove(graphic)
class Ellipse(Graphic):
def __init__(self, name):
self.name = name
def render(self):
print("Ellipse: {}".format(self.name))
if __name__ == '__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()
### OUTPUT ###
# Ellipse: 1
# Ellipse: 2
# Ellipse: 3
# Ellipse: 4
composite.py
