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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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Merged
StanFromIreland merged 4 commits into from
Jun 26, 2026
Merged

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

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c89a533
gh-152246: Reject a POSIX TZ Mm.w.d rule with a non-period separator …
tonghuaroot Jun 26, 2026
5c545bd
Add trailing newline to NEWS entry
tonghuaroot Jun 26, 2026
d3adcf7
Simplify NEWS entry
tonghuaroot Jun 26, 2026
72f1374
Apply suggestions from code review
StanFromIreland Jun 26, 2026
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gh-152246: Reject a POSIX TZ Mm.w.d rule with a non-period separator … 
…in pure-Python zoneinfo
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@tonghuaroot
tonghuaroot committed Jun 26, 2026
commit c89a5338f3ebf5c8bbf5cd867804496fa4962c75
5 changes: 5 additions & 0 deletions Lib/test/test_zoneinfo/test_zoneinfo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1184,6 +1184,11 @@ def test_invalid_tzstr(self):
# Invalid weekday
"AAA4BBB,M1.1.7/2,M2.1.1/2",
"AAA4BBB,M1.1.1/2,M2.1.7/2",
# Invalid Mm.w.d separator (must be a literal '.')
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"AAA4BBB,M3.2X0,M11.1.0",
"AAA4BBB,M3.2.0,M11.1X0",
"AAA4BBB,M3.2-0,M11.1.0/3",
"AAA4BBB,M3.2.0/2,M11.1:0",
# Invalid numeric offset
"AAA4BBB,-1/2,20/2",
"AAA4BBB,1/2,-1/2",
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2 changes: 1 addition & 1 deletion Lib/zoneinfo/_zoneinfo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -707,7 +707,7 @@ def _parse_dst_start_end(dststr):
type = date[:1]
if type == "M":
n_is_julian = False
m = re.fullmatch(r"M(\d{1,2})\.(\d).(\d)", date, re.ASCII)
m = re.fullmatch(r"M(\d{1,2})\.(\d)\.(\d)", date, re.ASCII)
if m is None:
raise ValueError(f"Invalid dst start/end date: {dststr}")
date_offset = tuple(map(int, m.groups()))
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6 changes: 6 additions & 0 deletions Misc/NEWS.d/next/Library/2026-06-26-12-50-26.gh-issue-152246.MfXMd1.rst
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@@ -0,0 +1,6 @@
Fixed a parity bug in the pure-Python :mod:`zoneinfo` implementation, which
accepted a POSIX TZ ``Mm.w.d`` transition rule whose third separator was not a
period (for example ``M3.2X0``). Only the first period was escaped in the
regular expression, so the third one matched any character. Such a string is
invalid per POSIX and is already rejected by the C accelerator. Patch by
tonghuaroot.
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