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[Python-Dev] __init_subclass__ is a class method (Was: Make __class_getitem__ a class method)

Ivan Levkivskyi levkivskyi at gmail.com
Fri Dec 15 17:48:10 EST 2017 
On 15 December 2017 at 18:40, Serhiy Storchaka <storchaka at gmail.com> wrote:

> 15.12.17 19:04, Ivan Levkivskyi пише:
>
>> Good point! Pure Python will be the primary use case and we have another
>> precedent
>> for "automatic" class method: __init_subclass__ (it does not need to be
>> decorated).
>>
>
> __init_subclass__ is very different beast, and parallels with it can be
> confusing. It is automatically decorated with classmethod if it is a
> regular function implemented in C. The following two examples are totally
> equivalent:
>
> class A:
>     def __init_subclass__(cls): pass
>
> class B:
>     @classmethod
>     def __init_subclass__(cls): pass
>
> help(A) shows __init_subclass__() as a class method (in 3.7).
>
> But if you implement the class in C you need to make __init_subclass__ a
> class method.
>
> I think __init_subclass__ should be documented as a class method since it
> is a class method.
>

Thank you for clarification!
Actually documentation
https://docs.python.org/3.6/reference/datamodel.html#customizing-class-creation
already says `classmethod object.__init_subclass__(cls)`
I am not an expert in this, so I am not sure if the docs can be improved
here (maybe we can add how this works with C API?)

--
Ivan
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