python基础第二十一课--OOP委托模式（小白piao分享）

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 ...
<bound method Gunner.do_exam of <__main__.Gunner object at 0x000001ED72CB4908>>
'''

代理机制的例子

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