策略模式

#coding:utf-8

class Duck:
def __init__(self):
self.fly_behavior = FlyNoWay()

# 把飞的动作托付给FlyBehavior对象的子类
def perform_fly(self):
self.fly_behavior.fly()

def set_fly_behavior(self, fly_behavior):
self.fly_behavior = fly_behavior

# 不同的飞翔方法，都继承FlyBehavior
class FlyBehavior:
def fly(self):
raise NotImplemented()

class FlyWithWings(FlyBehavior):
def fly(self):
print 'fly with wings'

class FlyNoWay(FlyBehavior):
def fly(self):
print 'can not fly'

if __name__ == '__main__':
d=Duck()
d.perform_fly()  #can not fly
d.set_fly_behavior(FlyWithWings())
d.perform_fly()  #fly with wings