[Python-Dev] Make __class_getitem__ a class method

[Ivan Levkivskyi]

On 15 December 2017 at 19:35, Serhiy Storchaka <storchaka at gmail.com> wrote:

> 15.12.17 20:02, Yury Selivanov пише:
>
>> But nobody decorates __new__ with a @staticmethod.  And making
>> __class_getitem__ a @classmethod will only confuse users -- that's all
>> I'm saying.
>>
>> So I'm +1 to keep the things exactly as they are now.  It would be
>> great do document that in order to implement __class_getitem__ in C
>> one should add it as METH_STATIC.  I also think we should merge your
>> PR that tests that it works the way it's expected.
>>
>
> In this case I suggest to make __class_getitem__ an automatic class method
> like __init_subclass__.
>
> The number of special cases bothers me.
>

I just want to clarify what is proposed. As I understand:

* From the point of view of a pure Python class there will be no difference
with the current behaviour, one just writes

      class C:
          def __class_getitem__(cls, item):
              ...

*  In `type_new`, `__class_getitem__` will be wrapped in classmethod
*  From the point of view of C extensions one will use METH_CLASS and no
tuple unpacking

If this is true that this looks reasonable. If no-one is against, then I
can make a PR.
The only downside to this that I see is that `type.__new__` will be
slightly slower.

--
Ivan
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