bridge.py

"""
*References:
http://en.wikibooks.org/wiki/Computer_Science_Design_Patterns/Bridge_Pattern#Python

*TL;DR
Decouples an abstraction from its implementation.
"""


# ConcreteImplementor 1/2
class DrawingAPI1:
 def draw_circle(self, x, y, radius):
 print("API1.circle at {}:{} radius {}".format(x, y, radius))


# ConcreteImplementor 2/2
class DrawingAPI2:
 def draw_circle(self, x, y, radius):
 print("API2.circle at {}:{} radius {}".format(x, y, radius))


# Refined Abstraction
class CircleShape:
 def __init__(self, x, y, radius, drawing_api):
 self._x = x
 self._y = y
 self._radius = radius
 self._drawing_api = drawing_api

 # low-level i.e. Implementation specific
 def draw(self):
 self._drawing_api.draw_circle(self._x, self._y, self._radius)

 # high-level i.e. Abstraction specific
 def scale(self, pct):
 self._radius *= pct


def main():
 """
 >>> shapes = (CircleShape(1, 2, 3, DrawingAPI1()), CircleShape(5, 7, 11, DrawingAPI2()))

 >>> for shape in shapes:
 ... shape.scale(2.5)
 ... shape.draw()
 API1.circle at 1:2 radius 7.5
 API2.circle at 5:7 radius 27.5
 """


if __name__ == "__main__":
 import doctest

 doctest.testmod()