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

Serhiy Storchaka storchaka at gmail.com
Fri Dec 15 12:40:06 EST 2017

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:
     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.

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