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gh-159706: Fix pure-Python ZoneInfo.fromutc() fold detection for single-transition zones - #159828

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pganssle merged 1 commit into
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lazerg:fix-issue-159706
Oct 21, 2026
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gh-159706: Fix pure-Python ZoneInfo.fromutc() fold detection for single-transition zones#159828
pganssle merged 1 commit into
python:mainfrom
lazerg:fix-issue-159706

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@lazerg

@lazerg lazerg commented Oct 20, 2026

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In the pure-Python fromutc(), a zone with exactly one transition takes the timestamp > self._trans_utc[-1] branch, which used self._ttinfos[-1] (the offset after the transition) as tti_prev. That made the shift zero, so times in the fold got fold=0. This uses self._tti_before like the C implementation does, and adds a test.

@bedevere-app bedevere-app Bot mentioned this pull request Oct 20, 2026
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pganssle merged commit 1c5b959 into python:main Oct 21, 2026
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@pganssle pganssle added 3.14 bugs and security fixes 3.15 bugs and security fixes needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 21, 2026
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miss-islington-app Bot commented Oct 21, 2026

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Thanks @lazerg for the PR, and @pganssle for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

@miss-islington-app

miss-islington-app Bot commented Oct 21, 2026

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Thanks @lazerg for the PR, and @pganssle for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

@bedevere-app

bedevere-app Bot commented Oct 21, 2026

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GH-160151 is a backport of this pull request to the 3.14 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Oct 21, 2026
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bedevere-app Bot commented Oct 21, 2026

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GH-160152 is a backport of this pull request to the 3.15 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Oct 21, 2026
StanFromIreland pushed a commit that referenced this pull request Oct 22, 2026
@miss-islington @lazerg
[3.15] gh-159706: Fix pure-Python ZoneInfo.fromutc() fold detection f…
568af27 
…or single-transition zones (GH-159828) (#160152)

(cherry picked from commit 1c5b959)

Co-authored-by: Lazizbek Ergashev <lazerg2@gmail.com>
StanFromIreland pushed a commit that referenced this pull request Oct 22, 2026
@miss-islington @lazerg
[3.14] gh-159706: Fix pure-Python ZoneInfo.fromutc() fold detection f…
f3059d6 
…or single-transition zones (GH-159828) (#160151)

(cherry picked from commit 1c5b959)

Co-authored-by: Lazizbek Ergashev <lazerg2@gmail.com>
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@pganssle pganssle pganssle approved these changes
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