New submission from Nick Coghlan:
Issue 10006 pointed out that attempting to access object.__abstractmethods__
raises AttributeError. The solution was to ensure type.__abstractmethods__
*also* raises AttributeError.
This is thoroughly confusing, since the name is clearly visible in the output
of dir(type). While it's technically legal for a descriptor to always raise
AttributeError, breaking the following typical assumed invariant is *highly*
dubious:
all(hasattr(obj, x) for x in dir(obj))
I see three main alternatives for improving the situation:
1. Make __abstractmethods__ a read-only descriptor that returns something
meaningful (like a frozenset(), the same as you get if you inherit from
abc.ABCMeta without defining any abstract methods)
2. Throw a better exception message that explains the broken invariant rather
than the generic "AttributeError with attribute name" that is currently thrown.
3. Implement type.__dir__ to filter out the uncooperative descriptor
----------
messages: 197755
nosy: ncoghlan
priority: normal
severity: normal
stage: needs patch
status: open
title: Improve handling of type.__abstractmethods__ descriptor
type: behavior
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue19022>
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