[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Irit Katriel]

Irit Katriel  added the comment:

PR27648 fixes this, but it also breaks test_abc.test_issubclass_bad_arguments 
so it's not quite right.


I don't know this area, but I think the problem is in the place the PR changes, 
and that the issue is due to this difference in the type of __subclasses__ 
between C and Meta2:

>>> class C: pass
... 
>>> from abc import ABCMeta
>>> class AbstractMeta(type, metaclass=ABCMeta): pass
... 
>>> class Meta2(AbstractMeta): pass
... 
>>> C.__subclasses__

>>> Meta2.__subclasses__


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versions: +Python 3.10, Python 3.11, Python 3.9 -Python 3.7

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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Irit Katriel]

Change by Irit Katriel :


--
keywords: +patch
nosy: +iritkatriel
nosy_count: 7.0 -> 8.0
pull_requests: +26142
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/27648

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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[myungsekyo]

Change by myungsekyo :


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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Caleb Donovick]

Change by Caleb Donovick :


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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Jeffrey Kintscher]

Change by Jeffrey Kintscher :


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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

I think this is related to how `__subclasscheck__` is implemented in `ABCMeta`. 
I just checked this also happens in Python 3.6 (i.e. it is not something 
specific to the C version introduced in Python 3.7).

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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Ivan Levkivskyi]

Change by Ivan Levkivskyi :


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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[SilentGhost]

Change by SilentGhost :


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nosy: +rhettinger, stutzbach
type:  -> behavior

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[issue36881] isinstance raises TypeError for metaclass with metaclass=ABCMeta

[Randy Eckman]

New submission from Randy Eckman :

>>> from abc import ABCMeta
>>> class AbstractMeta(type, metaclass=ABCMeta): pass
...
>>> class Meta1(AbstractMeta): pass
...
>>> class Meta2(AbstractMeta): pass
...
>>> class ClassA(metaclass=Meta1): pass
...
>>> isinstance(ClassA, Meta2)
Traceback (most recent call last):
  File "", line 1, in 
  File "C:\miniconda\miniconda3\lib\abc.py", line 139, in __instancecheck__
return _abc_instancecheck(cls, instance)
TypeError: __subclasscheck__() takes exactly one argument (0 given)


This is driven by the fact that the metaclass of AbstractMeta is ABCMeta; if I 
change its metaclass to something else that does not contain ABCMeta in the 
inheritance chain, isinstance returns False as expected.


Possibly related to Issue 2325?

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components: Interpreter Core
messages: 342152
nosy: emanspeaks
priority: normal
severity: normal
status: open
title: isinstance raises TypeError for metaclass with metaclass=ABCMeta
versions: Python 3.7

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