Is not this a PyPy issue that PySequence_Fast* functions do not work with lists and tuples?

The functions work for ret after calling PyObject* ret = PySequence_Fast(o), on both PyPy and CPython, but the documentation was not clear that this is always necessary. Hopefully now it is clearer.

@serhiy-storchaka: I think the point is that requiring those functions to work on lists and tuples puts nasty lifetime constraints on pypy, which could be lifted simply by relaxing the documentation to saying "PySequence_Fast_ITEMS is only defined on the result of PySequence_Fast".

I think this change needs more wide discussion. Please open an issue on the bug tracker and ask the question on the Python-Dev mailing list.

@mattip Hi, have you been able to open an issue on bugs.python.org about it as requested by Serhiy?

@serhiy-storchaka what do you see as controversial? Perhaps you could suggest a phrasing that would not require such an extensive discussion for a documentation clarification?

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

I have made the requested changes; please review again.

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@benjaminp: please review the changes made to this pull request.

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Thanks @mattip for the PR, and @benjaminp for merging it 🌮🎉.. I'm working now to backport this PR to: 2.7, 3.7, 3.8.
🐍🍒⛏🤖

GH-16068 is a backport of this pull request to the 3.8 branch.

GH-16069 is a backport of this pull request to the 3.7 branch.

Sorry, @mattip and @benjaminp, I could not cleanly backport this to 2.7 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 57b7dbc46e71269d855e644d30826d33eedee2a1 2.7