在python 3.6之前是否有类似__init_subclass __()的方法 [英] Is there any method like __init_subclass__() before python 3.6

问题描述

当我阅读Python Cookbook 3rd Edition食谱9.18时，我遇到了一个带有父类和一些可选参数的类定义，然后我进行了查找.我知道Python 3.6为父类添加了新功能 __ init_subclass __()方法，但是本书是基于Python 3.3编写的，因此，除了 metaclass 之外，哪种方法将采用这些参数?代码>?

When I read Python Cookbook 3rd Edition recipe 9.18, I ran into a class definition with parent Class and some optional argument, and I looked it up. I know that Python 3.6 added a new feature __init_subclass__() method for parent class, but the book is written based on Python 3.3, so what method will take these arguments other than a metaclass?

类定义在这里:

class Spam(Base, debug=True, typecheck=False):
    ...

我知道元类可以在其 __ prepare __ ， __ new __ ， __ init __ 方法中接受其他可选参数，但可以接受 Base code>是父类，这些参数在哪里?

I know that metaclass can accept other optional arguments in its' __prepare__, __new__, __init__ method, but Base is a parent class, where do these arguments go?

推荐答案

就像往常一样，它们转到元类的 __ prepare __ 方法.仅仅因为 Base 没有指定一个元类并不意味着它没有一个.默认的元类是 type .

They go to the metaclass's __prepare__ method, just like always. Just because Base hasn't specified a metaclass doesn't mean it doesn't have one. The default metaclass is type.

在Python 3.6中为 type 添加 __ init_subclass __ 只是节省了您定义自定义元类的工作，以实现与 __ init_subclass __ 你自己.

The addition of __init_subclass__ to type in Python 3.6 just saves you the effort of defining a custom metaclass in order to implement an equivalent to __init_subclass__ yourself.

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