gh-139819: rlcompleter – avoid suggesting attributes not accessible on instances

[ttw225]

Fix tab-completion suggesting names that are not accessible on instances
(e.g., Enum members showing __name__).

Change

In rlcompleter.attr_matches(), when getattr(thisobject, word, None)
is None, only add the candidate if hasattr(thisobject, word) is true.

Effect

Removes bogus suggestions without affecting valid completions.

Bogus suggestions

['Color.BLUE.__iter__',
'Color.BLUE.__getitem__',
'Color.BLUE.__members__',
'Color.BLUE.__contains__',
'Color.BLUE.__qualname__',
'Color.BLUE.__len__',
'Color.BLUE.__name__']
# Additionally seen among bogus suggestions:
'Enum.__abstractmethods__'

• Issue: rlcompleter suggests attributes not accessible on instances (e.g., Enum member __name__) #139819

[ttw225]

Noted the CI Test failure. I’m working on a fix and will push soon.

[ttw225]

Tests have passed. Thanks for reviewing!

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[danielhollas]

Should this use the new sentinel builtin?

[Viicos]

Opened #151222.