SRE: Atomic Grouping (?>...) is not supported

[effbot]

BPO	433030
Nosy	@birkenfeld, @terryjreedy, @ezio-melotti, @serhiy-storchaka
PRs	bpo-433030: Add support of atomic grouping in regular expressions #31982
Files	issue2636-01.patch re_atomic_groups.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 = None
closed_at = None
created_at = <Date 2001-06-14.08:30:56.000>
labels = ['expert-regex', 'type-feature', 'library', '3.11']
title = 'SRE: Atomic Grouping (?>...) is not supported'
updated_at = <Date 2022-03-21.16:28:37.831>
user = 'https://bugs.python.org/effbot'

bugs.python.org fields:

activity = <Date 2022-03-21.16:28:37.831>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'Regular Expressions']
creation = <Date 2001-06-14.08:30:56.000>
creator = 'effbot'
dependencies = []
files = ['10646', '37182']
hgrepos = []
issue_num = 433030
keywords = ['patch']
message_count = 12.0
messages = ['53164', '63284', '63288', '64634', '64735', '65777', '68337', '113201', '114621', '231041', '231049', '415685']
nosy_count = 10.0
nosy_names = ['effbot', 'georg.brandl', 'terry.reedy', 'rsc', 'timehorse', 'ezio.melotti', 'mrabarnett', 'THRlWiTi', 'abacabadabacaba', 'serhiy.storchaka']
pr_nums = ['31982']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue433030'
versions = ['Python 3.11']

[effbot]

from the jeffrey friedl report:

(?>...) is not supported

[this is a "stand-alone pattern". the engine has code
for this, but the parser doesn't recognize this yet.
shouldn't be too hard to fix; I just need a couple of
good test cases before I start /F]

[akuchling]

Also referred to as an atomic group: see
http://www.regular-expressions.info/atomic.html for a discussion.

Fredrik, when you say "the engine has code for this", what do you mean?

[akuchling]

There's also an alternate syntax for this, called possessive
quantifiers: a*+, a++, a{m,n}+.

[timehorse]

Fredrik,

If you're still listening, I am gonna try and tackle this one but I
would like to know why you or the famous Jeffrey of the Regexp world
claims that there is already code in the Regexp Engine for Atomic
Grouping? Adding a hook for (?>...) should be trivial but I don't wanna
re-invent the wheel if the proper stack-unwind code already exists.
Thanks. Of course, Andrew (a.k.a. A.M. Kuchling) already asked this
question and you did not answer it, so I guess you're not reading this,
but if you are, please respond. Thanks!

[timehorse]

I'm digging into the sre_parse.py at the moment and this I have all the
changes I need for that now. The rest of the changes I believe are in
either sre_compile.py or more likely directly in _sre.c, so I will
examine those files next. I am attaching a single diff for
expedience. This is not an official patch, just a sample to see the
progress I am making. I forgot the correct format for patch files but
I promise to get it right when I have made more progress.

[timehorse]

Quick update (see thread 2636 for other updates to the Regex
functionality): I do have a design in my mind for how to accomplish both
Atomic Grouping and Possessive Qualifiers and it would work with either
the existing Engine design or the new design I have been playing with.
It's just a matter of getting around to implementing it, testing it and
documenting it.

I currently am having problem with Bazaar / Launchpad which are beyond
the scope of this issue but are effecting my work. Those issues can be
found on the Launchpad site if you look for Answers / Bugs originating
from "timehorse".

[timehorse]

I have finished work on the Atomic Grouping / Possessive Qualifiers
support and am including a patch to achieve this; however,
http://bugs.python.org/issue2636 should be consulted for the complete list
of changes in the works for the Regexp engine.

[terryjreedy]

Does the re2 work (bpo-2636) make this outdated?

[birkenfeld]

Implemented in bpo-2636.

[serhiy-storchaka]

Some unrelated to the topic changes from the patch are committed in 30a6c74ad87f.

[serhiy-storchaka]

Reopened because definitely regex will be not adopted in 3.5.

Here is updated to 3.5 Jeffrey's patch.

[serhiy-storchaka]

New changeset 345b390 by Serhiy Storchaka in branch 'main':
bpo-433030: Add support of atomic grouping in regular expressions (GH-31982)
345b390

[hugovk]

Closing because GH-31982 has been merged.

[gpshead]

This feature addition led to #106052