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Title: re.LOCALE is nonsensical for Unicode
Type: enhancement Stage: resolved
Components: Extension Modules, Library (Lib), Regular Expressions, Unicode Versions: Python 3.5
Status: closed Resolution: fixed
Dependencies: 22838 Superseder:
Assigned To: serhiy.storchaka Nosy List: Arfrever, ezio.melotti, martin.panter, mrabarnett, pitrou, python-dev, serhiy.storchaka, vstinner
Priority: normal Keywords: patch

Created on 2014-09-14 15:43 by serhiy.storchaka, last changed 2022-04-11 14:58 by admin. This issue is now closed.

File name Uploaded Description Edit
re_unicode_locale.patch serhiy.storchaka, 2014-09-14 15:43 review
re_deprecate_unicode_locale.patch serhiy.storchaka, 2014-10-09 15:10 review
Messages (9)
msg226871 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2014-09-14 15:43
Current implementation of re.LOCALE support for Unicode strings is nonsensical. It correctly works only on Latin1 locales (because Unicode string interpreted as Latin1 decoded bytes string. all characters outside UCS1 range considered as non-words), on other locales it got strange and useless results.

>>> import re, locale
>>> locale.setlocale(locale.LC_CTYPE, 'ru_RU.cp1251')
>>> re.match(br'\w', 'µ'.encode('cp1251'), re.L)
<_sre.SRE_Match object; span=(0, 1), match=b'\xb5'>
>>> re.match(r'\w', 'µ', re.L)
<_sre.SRE_Match object; span=(0, 1), match='µ'>
>>> re.match(br'\w', 'ё'.encode('cp1251'), re.L)
<_sre.SRE_Match object; span=(0, 1), match=b'\xb8'>
>>> re.match(r'\w', 'ё', re.L)

Proposed patch fixes re.LOCALE support for Unicode strings. It uses the wide-character equivalents of C characters functions (towlower(), iswalpha(), etc).

The problem is that these functions are not exists in C89, they are introduced only in C99. Gcc understand them, we should check other compilers. However these functions are already used on FreeBSD and MacOS.
msg226949 - (view) Author: Antoine Pitrou (pitrou) * (Python committer) Date: 2014-09-16 12:36
I don't think we should fix this in 2.x: some people may rely on the old behaviour, and it will be difficult for them to debug.
In 3.x, I simply propose we deprecate re.LOCALE for unicode strings and make it a no-op.
msg226959 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2014-09-16 16:11
Yes, one of solution is to deprecate re.LOCALE for unicode strings and then 
make it incompatible with unicode strings. But I think it would be good to 
implement locale-aware matching.


>>> for a in 'Ii\u0130\u0131':
...     for b in 'Ii\u0130\u0131':
...         if a != b and re.match(a, b, re.I): print(a, '~', b)
I ~ i
I ~ İ
i ~ I
i ~ İ
İ ~ I
İ ~ i

This is incorrect result in Turkish. Capital dotless "I" matches capital "İ" 
with dot above, and small dotless "ı" doesn't match anything.

Regex produces more relevant output, which includes matches for Turkish and 

I ~ i
I ~ ı
i ~ I
i ~ İ
İ ~ i
ı ~ I

With locale tr_TR.utf8 (with the patch):

>>> for a in 'Ii\u0130\u0131':
...     for b in 'Ii\u0130\u0131':
...         if a != b and re.match(a, b, re.I|re.L): print(a, '~', b)
I ~ ı
i ~ İ
İ ~ i
ı ~ I

This is correct result in Turkish.

Therefore there is a use case for this feature.
msg226960 - (view) Author: Antoine Pitrou (pitrou) * (Python committer) Date: 2014-09-16 16:12
Ha, I always forget about the Turkish locale case...
msg228876 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2014-10-09 15:10
Here is simple patch which just deprecate using of the re.LOCALE flag with str patterns. It also deprecates using of the re.LOCALE flag with the re.ASCII flag (with bytes patterns) and adds some re.LOCALE related tests.
msg231022 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2014-11-11 11:06
If there are no objections I'll commit the re_deprecate_unicode_locale.patch patch. But it would be good if someone will review doc changes.
msg231924 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2014-12-01 10:38
Looks like revision 561d1d0de518 was to fix this issue, but the NEWS entry has the wrong reference number
msg231927 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2014-12-01 10:49
Indeed. Thank you Martin.
msg231931 - (view) Author: Roundup Robot (python-dev) (Python triager) Date: 2014-12-01 11:16
New changeset abc7fe393016 by Serhiy Storchaka in branch 'default':
Fixed issue number in Misc/NEWS for issue #22407.
Date User Action Args
2022-04-11 14:58:08adminsetgithub: 66597
2014-12-01 11:16:44python-devsetnosy: + python-dev
messages: + msg231931
2014-12-01 10:49:06serhiy.storchakasetmessages: + msg231927
2014-12-01 10:38:05martin.pantersetnosy: + martin.panter
messages: + msg231924
2014-12-01 09:53:48serhiy.storchakasetstatus: open -> closed
type: behavior -> enhancement
resolution: fixed
stage: patch review -> resolved
2014-11-11 11:06:22serhiy.storchakasetmessages: + msg231022
2014-11-11 11:02:03serhiy.storchakasetdependencies: + Convert re tests to unittest
2014-11-11 10:58:37serhiy.storchakasetassignee: serhiy.storchaka
2014-10-09 15:10:21serhiy.storchakasetfiles: + re_deprecate_unicode_locale.patch

messages: + msg228876
versions: - Python 2.7, Python 3.4
2014-09-21 09:27:33Arfreversetnosy: + Arfrever
2014-09-16 16:12:50pitrousetmessages: + msg226960
2014-09-16 16:11:02serhiy.storchakasetmessages: + msg226959
2014-09-16 12:36:32pitrousetmessages: + msg226949
2014-09-16 12:11:17vstinnersetcomponents: + Unicode
2014-09-16 12:11:10vstinnersetnosy: + vstinner
2014-09-14 15:43:18serhiy.storchakacreate