gh-121645: Add PyBytes_Join() function

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• Issue: [C API] Add PyBytes_Join() function #121645

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📚 Documentation preview 📚: https://cpython-previews--121646.org.readthedocs.build/

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cc @erlend-aasland@serhiy-storchaka

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@serhiy-storchaka: Please review the updated PR. I tried to address most of your comments.

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@serhiy-storchaka: I addressed most of your comments, except of the one one the doc:

NULL which is treated as an empty string.

[serhiy-storchaka]

LGTM, but please discuss first the behavior for the NULL separator.

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@encukou: I updated the PR to address your review.

[cdce8p]

@vstinner This might need a merge / rebase after #122267.

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@vstinner This might need a merge / rebase after #122267.

Done.

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I created capi-workgroup/decisions#36

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I created capi-workgroup/decisions#36

It was decided to reject NULL separator. I updated my PR to respect the C API Working Group decision.

I also rebased the PR to fix merge conflicts.

@erlend-aasland@encukou@serhiy-storchaka: Would you mind to review the updated PR?

[serhiy-storchaka]

Please do not use rebase so later in the review. So I do not see difference with already reviewed code and need to re-read all from the start.

Last two days I have power only for 2 intervals of 2 hours per day, so new review may take a time.

[vstinner]

Please do not use rebase so later in the review.

Do you mean that rebasing on main is bad, or is squashing commits which is bad for review? Sorry, I will avoid squashing commits next time.

[serhiy-storchaka]

Normally, I can find a link "changes since your last review". It is the best scenario.

If you rebased without squashing, I can still manually select recent commits. This is less convenient, and there is no guarantee that you did not modify previous commits.

If you squashed commits, all is lost. I do this only immediately after creating commit or pushing new changes, when there is a little chance that my previous change has been reviewed.

[encukou]

LGTM!

I second Serhiy's request to not rebase CPython PRs.

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Merged, thanks for reviews.