[thejesh23]

The "abstract base class" glossary entry mentions virtual subclasses but the
term had no entry of its own. This adds a short virtual subclass entry
(between "virtual machine" and "walrus operator") that explains:

• issubclass() and isinstance() treat a virtual subclass as a subclass of an
  ABC, even though it does not inherit from the ABC;
• a class is made one by ABCMeta.register(); an ABC can also recognize
  classes without registration via __subclasshook__();
• the ABC is not in its MRO, and it inherits none of the ABC's methods.

The existing mention in "abstract base class" now links to the new term. No
other text is changed.

Docs-only change, so this needs the skip news label.

AI disclosure: prepared with the help of Claude Code; I reviewed the change and the test results.

• Issue: Glossary doesn't have an entry for "virtual subclass" #161007

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Documentation build overview

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50 files changed · ± 50 modified

± Modified

• glossary.html
• builtins/stdtypes.html
• deprecations/pending-removal-in-3.15.html
• howto/enum.html
• howto/regex.html
• howto/sorting.html
• library/abc.html
• library/argparse.html
• library/binascii.html
• library/configparser.html
• and 40 more...

[sirosen]

I'm open to alternative opinions, but I think we can improve the text by striking a little bit, and no additional edits.

[thejesh23]

Thanks @sirosen, agreed on both points. I dropped the last two sentences. I have made the requested changes; please review again.

[bedevere-app]

Thanks for making the requested changes!

: please review the changes made to this pull request.

[sirosen]

Awesome! I think this is a good addition.

It occurs to me that "virtual subclass" could be used to describe any situation with ABC-like specialized subclass checks. But I think it's best as stated: narrow and easy to understand.

@nedbat, since you filed the original issue, I'm curious what you think.