Add 'The Python 2.3 Method Resolution Order'

[hugovk]

Follow on from python/pythondotorg#2392.

Add "The Python 2.3 Method Resolution Order" document from https://www.python.org/download/releases/2.3/mro/ to the docs as an explanation.

Source reST taken from https://github.com/mdipierro/demo.python.org/blob/master/private/data/127.0.0.1/en/2.3/mro/mro.txt with minor formatting and link updates.

---

📚 Documentation preview 📚: https://cpython-previews--116435.org.readthedocs.build/

[hugovk]

Doctest is failing for this file, but we don't want to run it all here.

Rather than adding # doctest: +SKIP to each block, can we skip the whole file?

[encukou]

3 failing doctests are for the old behaviour (Python 2.2/old-style classes), SKIP would make sense to me there.
For the A.mro() one, IMO it would make sense to remove __main__. from the expected output (and add # doctest: +NORMALIZE_WHITESPACE).

I'm not sure we can use Joan G. Stark's ASCII art snakes, unfortunately. It seems the terms of use are here: https://web.archive.org/web/20091028023223/http://www.geocities.com/SoHo/7373/please.htm
I guess they're fine on python.org directly, but for the docs we do allow redistribution for commercial/non-personal use.

[hugovk]

3 failing doctests are for the old behaviour (Python 2.2/old-style classes), SKIP would make sense to me there. For the A.mro() one, IMO it would make sense to remove __main__. from the expected output (and add # doctest: +NORMALIZE_WHITESPACE).

Updated!

I'm not sure we can use Joan G. Stark's ASCII art snakes, unfortunately. It seems the terms of use are here: web.archive.org/web/20091028023223/http://www.geocities.com/SoHo/7373/please.htm I guess they're fine on python.org directly, but for the docs we do allow redistribution for commercial/non-personal use.

That's too bad, but thanks for checking. Removed!

[hugovk]

@encukou Okay to merge now?

[encukou]

Yes, looks good. Thank you!

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @hugovk, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 7d0be7aea569b3bc9a3936501d7d32af87c70e73 3.12

[bedevere-app]

GH-117885 is a backport of this pull request to the 3.12 branch.