# -*- encoding=utf-8 -*-

"""

proxy 模式

一个常见的用法就是延迟实际的求值操作

"""

class Rectangle(object):

def __init__(self, height, width):

print 'Create a Rectangle'

self._height = height

self._width = width

def draw(self):

print 'A rectangle of size: {height}x{width} = {size}'.format(height=self._height,

width=self._width,

size=self._width*self._height)

class RectangleProxy(object):

def __init__(self, height, width):

print 'Create a Proxy'

self.height = height

self.width = width

self._last_height = height

self._last_width = width

self._instance = None

def draw(self):

if not self._instance \

or self._last_width != self.width \

or self._last_height != self.height:

self._instance = Rectangle(self.height, self.width)

self._last_height = self.height

self._last_width = self.width

self._instance.draw()

if __name__ == '__main__':

height, width = 10, 20

rectangle = RectangleProxy(height, width)

rectangle.draw()

rectangle.width = 30

rectangle.draw()