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gh-152246: Fix pure-Python `zoneinfo` accepting invalid seperators in POSIX TZ (`Mm.w.d`) rules by tonghuaroot · Pull Request #152247 · python/cpython · GitHub

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gh-152246: Fix pure-Python zoneinfo accepting invalid seperators in POSIX TZ (Mm.w.d) rules - #152247

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StanFromIreland merged 4 commits into
python:mainfrom
tonghuaroot:gh-152246-zoneinfo-mmwd-separator
Jun 26, 2026
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gh-152246: Fix pure-Python zoneinfo accepting invalid seperators in POSIX TZ (Mm.w.d) rules#152247
StanFromIreland merged 4 commits into
python:mainfrom
tonghuaroot:gh-152246-zoneinfo-mmwd-separator

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tonghuaroot commented Jun 26, 2026 •
edited by bedevere-app Bot
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The pure-Python zoneinfo parser accepted a POSIX TZ Mm.w.d transition rule whose third separator was not a period. Only the first separator is escaped in the regex (r"M(\d{1,2})\.(\d).(\d)"); the bare third . matches any single character, so for example EST5EDT,M3.2X0,M11.1.0 was accepted with X consumed as the separator. POSIX requires literal periods and the C accelerator already rejects these strings, so this is a pure-vs-C parity bug.

This escapes the third separator (\.) so the pure parser matches the C accelerator and POSIX. Every well-formed Mm.w.d rule and all bundled IANA zones still parse; only the previously-accepted malformed separators now raise ValueError.

bedevere-app Bot mentioned this pull request Jun 26, 2026
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StanFromIreland approved these changes Jun 26, 2026
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Comment thread Misc/NEWS.d/next/Library/2026-06-26-12-50-26.gh-issue-152246.MfXMd1.rst Outdated
Comment thread Lib/test/test_zoneinfo/test_zoneinfo.py Outdated
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Co-authored-by: Stan Ulbrych <stan@python.org>

StanFromIreland commented Jun 26, 2026 •
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The POSIX spec isn't actually explicit here, and doesn’t provide a formal grammar, but this is clearly a regex-typo (and doesn’t really make much sense in practice to allow other separators). Additionally, it's consistent with the far more used C implementation. As such, LGTM.

StanFromIreland changed the title gh-152246: Reject a POSIX TZ Mm.w.d rule with a non-period separator in pure-Python zoneinfo gh-152246: Fix pure-Python zoneinfo accepting invalid seperators in POSIX TZ (Mm.w.d) rules Jun 26, 2026
StanFromIreland added needs backport to 3.13 only security fixes needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Jun 26, 2026
StanFromIreland merged commit f47acc7 into python:main Jun 26, 2026
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miss-islington-app Bot commented Jun 26, 2026

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Thanks @tonghuaroot for the PR, and @StanFromIreland for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

bedevere-app Bot commented Jun 26, 2026

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GH-152265 is a backport of this pull request to the 3.15 branch.

bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Jun 26, 2026

bedevere-app Bot commented Jun 26, 2026

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GH-152266 is a backport of this pull request to the 3.14 branch.

bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Jun 26, 2026

bedevere-app Bot commented Jun 26, 2026

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GH-152267 is a backport of this pull request to the 3.13 branch.

bedevere-app Bot removed the needs backport to 3.13 only security fixes label Jun 26, 2026

StanFromIreland commented Jun 26, 2026

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Merged, thanks.

StanFromIreland added a commit that referenced this pull request Jun 26, 2026
[3.13] gh-152246: Fix pure-Python zoneinfo accepting invalid sepera…
82a5489 
…tors in POSIX TZ rules (GH-152247) (#152267)

(cherry picked from commit f47acc7)

Co-authored-by: tonghuaroot (童话) <tonghuaroot@gmail.com>
Co-authored-by: Stan Ulbrych <stan@python.org>
StanFromIreland added a commit that referenced this pull request Jun 26, 2026
[3.14] gh-152246: Fix pure-Python zoneinfo accepting invalid sepera…
683e9b9 
…tors in POSIX TZ rules (GH-152247) (#152266)

(cherry picked from commit f47acc7)

Co-authored-by: tonghuaroot (童话) <tonghuaroot@gmail.com>
Co-authored-by: Stan Ulbrych <stan@python.org>
StanFromIreland added a commit that referenced this pull request Jun 26, 2026
[3.15] gh-152246: Fix pure-Python zoneinfo accepting invalid sepera…
41f5b92 
…tors in POSIX TZ rules (GH-152247) (#152265)

(cherry picked from commit f47acc7)

Co-authored-by: tonghuaroot (童话) <tonghuaroot@gmail.com>
Co-authored-by: Stan Ulbrych <stan@python.org>
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