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metaclass， new 和 init 的解释有点小问题 #5

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xxleyi opened this issue May 26, 2019 · 0 comments

xxleyi commented May 26, 2019 •

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BAT_interviews/Python面试题及答案.md at master · lengyue1024/BAT_interviews

__new__和__init__ 解释：

__metaclass__是创建类时起作用.所以我们可以分别使用__metaclass__,__new__和__init__来分别在类创建,实例创建和实例初始化的时候做一些小手脚.

此处有点小问题：元类中也有 __new__，在类创建时也会调用一次，类中的 __new__ 其实是继承自元类（可以通过重写添加行为）~~，只有在重写过的情况下才会在每次新建实例时调用一次~~。这样一来，说 __new__ 在实例创建时做一些小手脚就有一丢丢的误导性。

修正：__new__ 作为 object 中就存在的静态方法，在类创建和实例创建时，均会调用，并可以通过重写定制类创建和实例创建的具体行为。

class T:
    pass

t = T()
t.__new__ is T.__new__ # True
T.__new__ is object.__new__ # True

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