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BPO	11957
Nosy	@rhettinger, @terryjreedy, @vstinner, @ericvsmith, @jwilk, @ezio-melotti, @merwok, @serhiy-storchaka
Dependencies	bpo-23591: enum: Add Flags and IntFlags
Files	patch_11957 re_keyword_only.patch re_check_flags_type.patch re_deprecate_positional_count.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/ezio-melotti'
closed_at = None
created_at = <Date 2011-04-29.18:27:10.198>
labels = ['expert-regex', 'type-feature', '3.7']
title = 're.sub confusion between count and flags args'
updated_at = <Date 2017-04-14.18:55:29.189>
user = 'https://bugs.python.org/mindauga'

bugs.python.org fields:

activity = <Date 2017-04-14.18:55:29.189>
actor = 'jwilk'
assignee = 'ezio.melotti'
closed = False
closed_date = None
closer = None
components = ['Regular Expressions']
creation = <Date 2011-04-29.18:27:10.198>
creator = 'mindauga'
dependencies = ['23591']
files = ['30821', '37067', '44825', '44826']
hgrepos = []
issue_num = 11957
keywords = ['patch']
message_count = 27.0
messages = ['134806', '134820', '134830', '135371', '135386', '135391', '136657', '143520', '186784', '186825', '186832', '186844', '186856', '192416', '230223', '230224', '230226', '230236', '230237', '230238', '230358', '230375', '277386', '277398', '291655', '291659', '291677']
nosy_count = 13.0
nosy_names = ['rhettinger', 'terry.reedy', 'vstinner', 'eric.smith', 'jwilk', 'ezio.melotti', 'eric.araujo', 'mrabarnett', 'python-dev', 'mindauga', 'serhiy.storchaka', 'mmilkin', 'umi']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue11957'
versions = ['Python 3.6', 'Python 3.7']

Linked PRs

Reacted by Matúš Ferech

Activity

mindauga commented on Apr 29, 2011
mindaugamannequin
on Apr 29, 2011
MannequinAuthor
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re.sub don't substitute not ASCII characters:

Python 2.7.1 (r271:86832, Apr 15 2011, 12:11:58) Arch Linux

>>import re

>>a=u'aaa'
>>print re.search('(\w+)',a,re.U).groups()
(u'aaa')
>>print re.sub('(\w+)','x',a,re.U)
x

BUT:

>>a=u'ąąą'
>>print re.search('(\w+)',a,re.U).groups()
(u'\u0105\u0105\u0105')
>>print re.sub('(\w+)','x',a,re.U)
ąąą
mindauga
added
topic-unicode

topic-regex
on Apr 29, 2011
ericvsmith commented on Apr 29, 2011
ericvsmith
on Apr 29, 2011
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The 4th parameter to re.sub() is a count, not flags.
Reacted by arsen671games3
ezio-melotti commented on Apr 30, 2011
ezio-melotti
on Apr 30, 2011
Member
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Since this has been reported already several times (see e.g. bpo-11947), and it's a fairly common mistake, I think we should do something to avoid it.

A few possibilities are:

add a warning in the doc;

make count and flag keyword-only argument (raising a deprecation warning in 3.3 and actually change it later);

change the regex flags to some object that can be distinguished from ints and raise an error when a flag is passed to count;
ezio-melotti
changed the title ~~[-]re.sub problem with unicode string[/-]~~ [+]re.sub confusion between count and flags args[/+] on Apr 30, 2011
terryjreedy commented on May 6, 2011
terryjreedy
on May 6, 2011
Member
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I like the idea of an internal REflag class with __new__, __or__, and __repr__==str. Str(re.A|re.L) might print as
"REflag: re.ASCII | re.IGNORE"
If it is *not* an int subclass, any attempt to use or mix with an int would raise. I checked and the doc only promises that flags can be or'ed. An __and__ method might be added if it were thought that people currently use & to check for flags set, though that is not currently promised.
mrabarnett commented on May 6, 2011
mrabarnettmannequin
on May 6, 2011
Mannequin
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Something like "<re.Flag ASCII | IGNORE>" may be more Pythonic.
terryjreedy commented on May 7, 2011
terryjreedy
on May 7, 2011
Member
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Agreed, if we go that route.
rhettinger
self-assigned this
on May 14, 2011
merwok commented on May 23, 2011
merwok
on May 23, 2011
Member
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I’d favor 1) or 2) over 3). Ints are short and very commonly used for flags.
ezio-melotti commented on Sep 5, 2011
ezio-melotti
on Sep 5, 2011
Member
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See also bpo-12888 for an error in the stdlib caused by this.
ezio-melotti
added
type-featureA feature request or enhancementA feature request or enhancement
on Apr 10, 2013
mmilkin commented on Apr 13, 2013
mmilkinmannequin
on Apr 13, 2013
Mannequin
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I like option #2, and I was thinking of working on it today, poke me if anyone has a problem with this.
mmilkin commented on Apr 13, 2013
mmilkinmannequin
on Apr 13, 2013
Mannequin
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There is no sane way to issue a warning without changing the signature and we don't want to change the signature without issuing a deprecation warning for the function, so sadly option 3 is the only way for this to work, (Im going to not touch this till ENUMS are merged in.)
29 remaining items
serhiy-storchaka
closed this as completed on Aug 17, 2023
tchaikov
added a commit that references this issue on Sep 27, 2024
test.py: pass "count" to re.sub() with kwarg
8b833d8
xemul
added a commit that references this issue on Sep 30, 2024
test.py: pass "count" to re.sub() with kwarg
c3be4a3
paul-elliott-arm
added a commit that references this issue on Oct 25, 2024
Remove deprecated use of count as positional arg
03b11fb
paul-elliott-arm
added a commit that references this issue on Nov 13, 2024
Remove deprecated use of count as positional arg
59ec32a
tchaikov
added 2 commits that reference this issue on Dec 31, 2024
test.py: pass "count" to re.sub() with kwarg
e4a46d6
test.py: pass "count" to re.sub() with kwarg
4fb8ee9
avikivity
added a commit that references this issue on Jan 6, 2025
test.py: pass "count" to re.sub() with kwarg
8873a4e
aarongable
added a commit that references this issue on Feb 25, 2025
crashpad: fix update.py DeprecationWarning under Python 3.13
df2f36f
hubot
added a commit that references this issue on Feb 25, 2025
Fix Python 3.13 re DeprecationWarning: pass count and flags by keyword
51eba29
gm4sl
added a commit that references this issue on Apr 1, 2025
Fix Python 3.13 re DeprecationWarning: pass count and flags by keyword
80a21e5
millerdev
added 3 commits that reference this issue on Apr 8, 2025
'maxsplit' should not be passed as positional argument
a0dce04
'maxsplit' should not be passed as positional argument
497e4ca
'maxsplit' should not be passed as positional argument
5c276d2
lastnameis-borah
added a commit that references this issue on Feb 2, 2026
artiq_flash: Fix incorrect re.sub() call
f54629b

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GeezerVison

re.sub confusion between count and flags args #56166

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mindauga commented on Apr 29, 2011

ericvsmith commented on Apr 29, 2011

ezio-melotti commented on Apr 30, 2011

terryjreedy commented on May 6, 2011

mrabarnett commented on May 6, 2011

terryjreedy commented on May 7, 2011

merwok commented on May 23, 2011

ezio-melotti commented on Sep 5, 2011

mmilkin commented on Apr 13, 2013

mmilkin commented on Apr 13, 2013

29 remaining items

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