[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[Inada Naoki]

Change by Inada Naoki :


--
resolution:  -> not a bug
stage: patch review -> resolved
status: open -> closed

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

I totally agree with Serhiy

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I don't like complicating the code and adding a performance penalty to support 
such uncommon case.

The documentation for __class_getitem__ precisely describes the current 
behavior: "when defined in the class body, this method is implicitly a class 
method". Nothing should be changed here.

The documentation for __init_subclass__ could be rewritten in similar words.

--
nosy: +serhiy.storchaka

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[INADA Naoki]

INADA Naoki  added the comment:

__new__ is special function too.  It is converted as staticmethod when class 
creation.

Since manually converting to (static|class)method is allowed, I don't think
automatic conversion should be applied when attach after class creation.

$ python3
Python 3.7.2 (default, Feb 12 2019, 08:15:36)
[Clang 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class C:
...   def __new__(cls):
... pass
...
>>> type(C.__dict__['__new__'])

>>> class D:
...   pass
...
>>> D.__new__ = lambda cls: cls
>>> type(D.__dict__['__new__'])


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nosy: +inada.naoki

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[Raymond Hettinger]

Raymond Hettinger  added the comment:

> CPython only makes these methods class method when a class created.
> If you set __class_getitem__ method after the creation it 
> doesn't work unless you use classmethod decorator manually.

Give the intended use case for __class_getitem__ and that it was replacement 
for metaclass code with the same effect, the current behavior doesn't seem 
unreasonable.  That said, I don't see any downside to allowing the method to 
attach after class creation.

Assigning to Ivan to make the call on this one.

--
assignee:  -> levkivskyi
components: +Interpreter Core
nosy: +rhettinger
type: behavior -> enhancement
versions: +Python 3.8

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[Rémi Lapeyre]

Rémi Lapeyre  added the comment:

Is this an issue though? Shouldn't methods be defined in the class definition, 
we don't expect setting a function as an attribute to a class to transform it 
automatically to a method.

Why would we special case __class_getitem__ and not __init_subclass__?

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nosy: +remi.lapeyre

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


--
nosy: +levkivskyi

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[BTaskaya]

Change by BTaskaya :


--
keywords: +patch
pull_requests: +11967
stage:  -> patch review

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[issue36042] Setting __init_subclass__ and __class_getitem__ methods are in runtime doesnt make them class method.

[BTaskaya]

New submission from BTaskaya :

CPython only makes these methods class method when a class created. If you set 
__class_getitem__ method after the creation it doesn't work unless you use 
classmethod decorator manually.

>>> class B:
... pass
... 
>>> def y(*a, **k):
... return a, k
... 
>>> B.__class_getitem__ = y 
>>> B[int]
((,), {})
>>> B.__class_getitem__ = classmethod(y)
>>> B[int]
((, ), {})

--
messages: 335985
nosy: BTaskaya
priority: normal
severity: normal
status: open
title: Setting __init_subclass__ and __class_getitem__ methods are in runtime 
doesnt make them class method.
type: behavior

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