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  • day33---属性查找

    结合python继承的实现原理+元类重新看属性的查找应该是什么样子呢???

    在学习完元类后,其实我们用class自定义的类也全都是对象(包括object类本身也是元类type的 一个实例,可以用type(object)查看),我们学习过继承的实现原理,如果把类当成对象去看,将下述继承应该说成是:对象StanfordTeacher继承对象Foo,对象Foo继承对象Bar,对象Bar继承对象object

    class Mymeta(type):
        n=444
    
        def __call__(self, *args, **kwargs): #self=<class '__main__.StanfordTeacher'>
            obj=self.__new__(self) # StanfordTeacher.__new__
            # obj=object.__new__(self)
            print(self.__new__ is object.__new__) #True
            self.__init__(obj,*args,**kwargs)
            return obj
    
    class Bar(object):
        # n=333
    
        # def __new__(cls, *args, **kwargs):
        #     print('Bar.__new__')
        pass
    
    class Foo(Bar):
        # n=222
    
        # def __new__(cls, *args, **kwargs):
        #     print('Foo.__new__')
        pass
    
    class StanfordTeacher(Foo,metaclass=Mymeta):
        # n=111
    
        def __init__(self,name,age):
            self.name=name
            self.age=age
    #
    #
    # obj=StanfordTeacher('lili',18)
    # print(obj.__dict__)
    # print(obj.n)
    print(StanfordTeacher.
    于是属性查找应该分成两层,一层是对象层(基于c3算法的MRO)的查找,另外一个层则是类层(即元类层)的查找
    
    对象发起的属性查找:找到object 停止查找
    类发起的属性查找:object没找到会继续寻找元类

    转自:https://zhuanlan.zhihu.com/p/109336845

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  • 原文地址:https://www.cnblogs.com/surpass123/p/12710205.html
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