[Python-Dev] init_subclass is a class method (Was: Make class_getitem a class method) (original) (raw)

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: initsubclass (it does not need to be decorated).

initsubclass 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 initsubclass(cls): pass class B: @classmethod def initsubclass(cls): pass help(A) shows initsubclass() as a class method (in 3.7). But if you implement the class in C you need to make initsubclass a class method. I think initsubclass 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?)

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