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re.compile(r'((x|y+)*)*') should not fail #46789
Description
| BPO | 2537 |
|---|---|
| Nosy | @ezio-melotti, @meadori, @serhiy-storchaka |
| Files |
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 = <Date 2013-08-19.20:43:29.768>
created_at = <Date 2008-04-02.17:36:05.061>
labels = ['expert-regex', 'type-bug', 'library']
title = "re.compile(r'((x|y+)*)*') should not fail"
updated_at = <Date 2013-08-19.20:43:29.766>
user = 'https://bugs.python.org/jorendorff'bugs.python.org fields:
activity = <Date 2013-08-19.20:43:29.766>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2013-08-19.20:43:29.768>
closer = 'serhiy.storchaka'
components = ['Library (Lib)', 'Regular Expressions']
creation = <Date 2008-04-02.17:36:05.061>
creator = 'jorendorff'
dependencies = []
files = ['16207']
hgrepos = []
issue_num = 2537
keywords = ['patch']
message_count = 9.0
messages = ['64865', '64934', '64950', '99194', '99237', '99248', '99251', '195662', '195664']
nosy_count = 8.0
nosy_names = ['rsc', 'timehorse', 'jorendorff', 'ezio.melotti', 'mrabarnett', 'meador.inge', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue2537'
versions = ['Python 2.7', 'Python 3.3', 'Python 3.4']
Activity
jorendorff commentedon Apr 2, 2008
Below, the second regexp seems just as guilty as the first to me.
I don't know if that error is to protect the sre engine from bad
patterns or just a courtesy to users. If the former, it could be a
serious bug.
mdickinson commentedon Apr 4, 2008
I'm almost tempted to call the first of these a bug: isn't '((x|y))'
a perfectly valid (albeit somewhat redundant) regular expression? What
am I missing here?
Even if there are issues with capturing, shouldn't the version without
capturing subexpressions still work?
I get:
>>> re.compile(r'(?:(?:x|y)*)*') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.5/re.py", line 180, in compile return _compile(pattern, flags) File "/usr/lib/python2.5/re.py", line 233, in _compile raise error, v # invalid expression sre_constants.error: nothing to repeatjorendorff commentedon Apr 4, 2008
Huh. Maybe you're right. JavaScript, Ruby, and Perl all accept both
regexes, although no two agree on what should be captured:
js> "xyyzy".replace(/((x|y))/, "($1, $2)")
(xyy, y)zy
js> "xyyzy".replace(/((x|y+))/, "($1, $2)")
(xyy, yy)zy
DB<1> $_ = 'xyyzy'; s/((x|y))/(\1 \2)/; print
( )zy
DB<2> $_ = 'xyyzy'; s/((x|y+))/(\1 \2)/; print
( yy)zy
Ruby's behavior seems best to me.
meadori commentedon Feb 11, 2010
We can obtain the Ruby behavior easily. There is one check in sre_compile.py in the '_simple' function that needs to be removed (see attached patch). Whether or not the Ruby behavior is the "correct" behavior I am still not sure. In any case, I think throwing an exception is to aggressive for this case.
mrabarnett commentedon Feb 11, 2010
The re module is addressed in issue bpo-2636.
BTW, my regex module behaves like Ruby:
meadori commentedon Feb 12, 2010
Wow, that issue thread is massive... What about the 're' module is addressed? Is 'regex' replacing 're'? Is 'regex' being rolled into 're'? Are they both going to exist?
mrabarnett commentedon Feb 12, 2010
The issue started about updating the re module and adding features that other languages already possess in their regex implementations (the last time any significant work was done on it was in 2003).
The hope is that the new regex implementation will eventually replace the existing one, and putting it initially in a module called 'regex' allows it to be tested more easily.
You can do:
and existing code should still work.
python-dev commentedon Aug 19, 2013
New changeset 7ab07f15d78c by Serhiy Storchaka in branch '3.3':
Issue bpo-2537: Remove breaked check which prevented valid regular expressions.
http://hg.python.org/cpython/rev/7ab07f15d78c
New changeset f4271cc2dfb5 by Serhiy Storchaka in branch 'default':
Issue bpo-2537: Remove breaked check which prevented valid regular expressions.
http://hg.python.org/cpython/rev/f4271cc2dfb5
New changeset 7b867a46a8b4 by Serhiy Storchaka in branch '2.7':
Issue bpo-2537: Remove breaked check which prevented valid regular expressions.
http://hg.python.org/cpython/rev/7b867a46a8b4
serhiy-storchaka commentedon Aug 19, 2013
This issue is a duplicate of bpo-1633953. See also bpo-18647. After some fixes in other parts of the re module this check has become even more invalid.
[-]re.compile(r'((x|y+)*)*') should fail[/-][+]re.compile(r'((x|y+)*)*') should not fail[/+]