[New-bugs-announce] [issue1109] Warning required when calling register() on an ABCMeta subclass

[Mark Summerfield]

New submission from Mark Summerfield:

GvR asked me to add this to the bug tracker.

If you do this:

    class A(ABCMeta): pass

    A.register(list)

you get this error message:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: maximum recursion depth exceeded in __instancecheck__

This is not very helpful.

You probably meant to write:

    class A(metaclass=ABCMeta): pass

Perhaps a warning message like this would be better:

"register() should not be called on an ABCMeta subclass; maybe you
forgot the metaclass keyword argument when declaring the class?"

----------
components: Interpreter Core
messages: 55663
nosy: mark
severity: normal
status: open
title: Warning required when calling register() on an ABCMeta subclass
type: behavior
versions: Python 3.0

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Tracker <report at bugs.python.org>
<http://bugs.python.org/issue1109>
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