[issue43594] Subclass of both `ABC` and `ABCMeta` breaks on `__subclasscheck__`

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

Verified on Win10 for 3.8-3.10.  3.6 only gets security fixes.

Guido, is the above a bug?  (There is no listed abc or 'metaclass' expert and I don't know.)

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nosy: +gvanrossum, terry.reedy
title: A metaclass that inherits both `ABC`  and `ABCMeta` breaks on `__subclasscheck__` -> Subclass of  both `ABC`  and `ABCMeta` breaks on `__subclasscheck__`
versions: +Python 3.10, Python 3.9 -Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43594>
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