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 intoJun 26, 2026
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StanFromIreland
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Jun 26, 2026
Co-authored-by: Stan Ulbrych <stan@python.org>
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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
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zoneinfo accepting invalid seperators in POSIX TZ (Mm.w.d) rules
StanFromIreland
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needs backport to 3.13
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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. |
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GH-152265 is a backport of this pull request to the 3.15 branch. |
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needs backport to 3.15
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GH-152266 is a backport of this pull request to the 3.14 branch. |
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GH-152267 is a backport of this pull request to the 3.13 branch. |
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Merged, thanks. |
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The pure-Python
zoneinfoparser accepted a POSIX TZMm.w.dtransition 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 exampleEST5EDT,M3.2X0,M11.1.0was accepted withXconsumed 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-formedMm.w.drule and all bundled IANA zones still parse; only the previously-accepted malformed separators now raiseValueError.Mm.w.drule accepts a non-.week/day separator (C rejects) #152246