Python入门精华OOP委托者模式

　　什么是委托模式？
　　委托者模式是指将类的一些属性委托到内部持有的一个对象上，让其完成一些工作的模式。目的：
　　作为继承的替代方案或为了实现一种代理机制。继承替代的例子：class Gunner:#抢手为被委托方 ---类似父类     def dohomework(self,name):         print(name,＂(gunnner) is doing homework ...＂,sep=＂＂)     def do_exam(self,name):         print(name,＂(gunnner) is examing...＂,sep=＂＂)  class Student:#类似子类     def __init__(self,name):         self._gunner = Gunner()         self.name = name     def do_homework(self):#雇佣抢手写作业         self._gunner.dohomework(self.name)     def do_exam(self):#雇佣抢手考试         self._gunner.do_exam(self.name)     def play(self):         print(＂I`m playing basketball ...＂)  小白piao = Student(＂小白piao＂) 小白piao.do_exam() 小白piao.do_homework() 小白piao.play() print(小白piao.__dict__)  #结果： ＂＂＂ 小白piao(gunnner) is examing... 小白piao(gunnner) is doing homework ... I`m playing basketball ... {＂_gunner＂: <__main__.Gunner object at 0x0000025E35B03898>, ＂name＂: ＂小白piao＂}  Process finished with exit code 0 ＂＂＂
　　如果被委托方仅仅只有个别方法被委托，则上述例子足矣，但是如果需要被委托方帮委托方做所有被委托方做的事情的话：一种方法是在委托方类中写上所有的调用被委托方方法的方法。另外一种更加轻松的方式如下：class Gunner:     def dohomework(self,name):         print(name,＂(gunnner) is doing homework ...＂,sep=＂＂)     def do_exam(self,name):         print(name,＂(gunnner) is examing...＂,sep=＂＂)     def play_soccer(self):         print(＂playing ...＂)  class Student:     def __init__(self,name):         self._gunner = Gunner()         self.name = name     def do_homework(self):         self._gunner.dohomework(self.name)     def do_exam(self):         self._gunner.do_exam(self.name)     def play(self):         print(＂I`m playing basketball ...＂)     def __getattr__(self, item):         return getattr(self._gunner,item)#得到gunner中名字为item的属性  小白piao = Student(＂小白piao＂) 小白piao.play_soccer() 小白piao.do_exam()#这个方法是自己的，和抢手方法同名 小白piao.dohomework(＂抢手＂)#这个方法是抢手的  print(小白piao.__getattr__(＂do_exam＂)) #结果： ＂＂＂ playing ... 小白piao(gunnner) is examing... 抢手(gunnner) is doing homework ... > ＂＂＂ 代理模式例子：class Proxy:     def __init__(self,obj):         self._obj = obj     def __getattr__(self, item):         return getattr(self._obj,item)     def __setattr__(self, key, value):         if key.startswith(＂_＂):             super(Proxy, self).__setattr__(key,value)         else:             setattr(self._obj,key,value)     def __delete__(self, instance):         if instance.startswith(＂_＂):             super(Proxy, self).__delete__(instance)         else:             delattr(self._obj,instance)  class Spam:     def __init__(self,value):         self.x = value     def bar(self,value):         print(＂bar spam:＂,self.x,value)  s = Spam(3) p = Proxy(s) print(p.x)#3 p.bar(37)#bar spam: 3 37 p.x = 30 p.y = 28 print(s.y)#28