bpo-39199: Add descriptions of non-deprecated AST nodes to the AST module documentation

[pablogsal]

These new descriptions are adapted from https://greentreesnakes.readthedocs.io

https://bugs.python.org/issue39199

[willingc]

@pablogsal Just getting back from vacation. Will look at this in the next day or so. Happy New Year too!

[willingc]

@pablogsal This is wonderful. Great job. A few little nits but this looks ready to merge. Thanks!

[JulienPalard]

LGTM, @pablogsal take a look at @willingc comments and it's good for me.

[takluyver]

I was slightly surprised when I consulted the AST module docs today to see that a large part of Green Tree Snakes has been incorporated with no visible attribution (in the docs themselves - I can see it's acknowledged in this PR).

I am pleased to see it there - I think this should have been part of the official AST docs in the first place, and I'm sure it will be kept up to date better here than as a random separate project. But at the same time, a fair amount of effort (mostly other contributors' in the last few years) went into creating and curating those descriptions. I would have expected someone to ask before republishing it.

I never actually got round to adding any kind of license to the GTS repo, though that's due to oversight & laziness rather than any objection to the idea. If I had, it would likely be something like CC-BY or BSD, though I'd be happy to waive the attribution requirements (as much as I can - other contributors retain their rights) if that was even a small obstacle to improving the Python docs.

If you think it's appropriate, I would be delighted to see a little note somewhere by this section mentioning something like "these descriptions of node classes were adapted from Green Tree Snakes". I think that's the easiest way to acknowledge something that many people have worked on. If there's no natural way to do this visibly in the documentation, I'd settle for the compromise of putting it in a comment in the rst source.

[pablogsal]

Thanks a lot for reaching out @takluyver !

If you think it's appropriate, I would be delighted to see a little note somewhere by this section mentioning something like "these descriptions of node classes were adapted from Green Tree Snakes". I think that's the easiest way to acknowledge something that many people have worked on. If there's no natural way to do this visibly in the documentation, I'd settle for the compromise of putting it in a comment in the rst source.

Absolutely, I think it makes sense. Let's add some visible attribution on the documentation itself! Would you mind reviewing the PR once I make it?

[takluyver]

Thanks! I'd be happy to review a PR.

[pablogsal]

Thanks! I'd be happy to review a PR.

Opened #24727