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GeezerVison is showing github.com — gh-156444: Fix a negated character set with IGNORECASE and LOCALE by serhiy-storchaka · Pull Request #156445 · python/cpython

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Aug 27, 2026 •
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charset_loc_ignore() tested the whole set once per locale case and returned true if either test matched. That complements a set before closing it under case rather than after, so [bc] matched b'B' and [^bc] matched it too.

It now walks the set itself and tries both cases for every member, which puts the closure on the members and leaves NEGATE complementing the closed set. SRE(charset) is untouched, and an uncased character short-circuits straight into it.

BIGCHARSET and RANGE_UNI_IGNORE are not handled: neither can occur in the set of a bytes pattern, and re.LOCALE rejects str patterns.

This also fixes gh-155985. The difference fusion is safe once the engine handles an embedded NEGATE correctly, so the workaround in GH-155993 is no longer needed:

>>> re.fullmatch(rb'\w(?<!b)', b'B', re.I | re.L)
>>> re.fullmatch(rb'[A-z--[0-m]]', b'N', re.I | re.L)

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@serhiy-storchaka @claude
pythongh-156444: Fix a negated character set with IGNORECASE and LOCALE
ded2f4c 
charset_loc_ignore() tested the whole set once per locale case and took
the disjunction, which complements a set before closing it under case
instead of after: [bc] matched b'B', but so did [^bc].  Match both cases
of the character against every set member instead.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
@bedevere-app bedevere-app Bot mentioned this pull request Aug 27, 2026
re.IGNORECASE | re.LOCALE: a negated character set matches the other case #156444
Closed
@bedevere-app bedevere-app Bot added the awaiting core review label Aug 27, 2026
@serhiy-storchaka serhiy-storchaka 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 Aug 27, 2026
@serhiy-storchaka
serhiy-storchaka merged commit 6671d27 into python:main Aug 27, 2026
108 of 110 checks passed

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@miss-islington-app

miss-islington-app Bot commented Aug 27, 2026

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Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖
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@bedevere-app bedevere-app Bot removed the awaiting core review label Aug 27, 2026
@serhiy-storchaka
serhiy-storchaka deleted the gh-156444-charset-loc-ignore branch August 27, 2026 11:11
@bedevere-app

bedevere-app Bot commented Aug 27, 2026

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GH-156456 is a backport of this pull request to the 3.15 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Aug 27, 2026
@bedevere-app

bedevere-app Bot commented Aug 27, 2026

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GH-156457 is a backport of this pull request to the 3.14 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Aug 27, 2026
@bedevere-app

bedevere-app Bot commented Aug 27, 2026

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GH-156458 is a backport of this pull request to the 3.13 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.13 only security fixes label Aug 27, 2026
serhiy-storchaka added a commit that referenced this pull request Aug 27, 2026
@miss-islington @serhiy-storchaka @claude
[3.14] gh-156444: Fix a negated character set with IGNORECASE and LOC…
9ac4200 
…ALE (GH-156445) (GH-156457)

charset_loc_ignore() tested the whole set once per locale case and took
the disjunction, which complements a set before closing it under case
instead of after: [bc] matched b'B', but so did [^bc].  Match both cases
of the character against every set member instead.
(cherry picked from commit 6671d27)

Co-authored-by: Serhiy Storchaka <[email protected]>
Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
serhiy-storchaka added a commit that referenced this pull request Aug 27, 2026
@miss-islington @serhiy-storchaka @claude
[3.13] gh-156444: Fix a negated character set with IGNORECASE and LOC…
7e7e88f 
…ALE (GH-156445) (GH-156458)

charset_loc_ignore() tested the whole set once per locale case and took
the disjunction, which complements a set before closing it under case
instead of after: [bc] matched b'B', but so did [^bc].  Match both cases
of the character against every set member instead.
(cherry picked from commit 6671d27)

Co-authored-by: Serhiy Storchaka <[email protected]>
Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
clin1234 pushed a commit to clin1234/cpython that referenced this pull request Aug 27, 2026
@serhiy-storchaka @claude @clin1234
pythongh-156444: Fix a negated character set with IGNORECASE and LOCA…
ed08b1f 
…LE (pythonGH-156445)

charset_loc_ignore() tested the whole set once per locale case and took
the disjunction, which complements a set before closing it under case
instead of after: [bc] matched b'B', but so did [^bc].  Match both cases
of the character against every set member instead.

Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
serhiy-storchaka added a commit that referenced this pull request Oct 10, 2026
@miss-islington @serhiy-storchaka @claude
[3.15] gh-156444: Fix a negated character set with IGNORECASE and LOC…
93de9ba 
…ALE (GH-156445) (GH-156456)

charset_loc_ignore() tested the whole set once per locale case and took
the disjunction, which complements a set before closing it under case
instead of after: [bc] matched b'B', but so did [^bc].  Match both cases
of the character against every set member instead.
(cherry picked from commit 6671d27)

Co-authored-by: Serhiy Storchaka <[email protected]>
Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
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Negative lookbehind ignored under re.IGNORECASE | re.LOCALE

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@serhiy-storchaka
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