Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.albasani.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed2a.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'operator': 0.03; 'debug': 0.07; 'subject:bug': 0.07; 'think,': 0.07; 'literal': 0.09; 'parsed': 0.09; 'parsing': 0.09; 'python': 0.11; 'bug': 0.12; 'translation': 0.12; '2.7': 0.14; 'question.': 0.14; '"":': 0.16; 'brace': 0.16; 'does,': 0.16; 'dot,': 0.16; 'expected,': 0.16; 'extraneous': 0.16; 'fine.': 0.16; 'from:addr:mrabarnett.plus.com': 0.16; 'from:addr:python': 0.16; 'from:name:mrab': 0.16; 'instance:': 0.16; 'message- id:@mrabarnett.plus.com': 0.16; 'received:192.168.1.4': 0.16; 'received:84.93': 0.16; 'received:84.93.230': 0.16; 'subject:expression': 0.16; 'subject:possible': 0.16; 'surprising': 0.16; 'sat,': 0.16; 'wrote:': 0.18; 'trying': 0.19; '>>>': 0.22; 'input': 0.22; 'header:User-Agent:1': 0.23; 'looks': 0.24; 'possibly': 0.26; 'this:': 0.26; 'header:In-Reply-To:1': 0.27; 'correct': 0.29; 'chris': 0.29; "we'd": 0.29; 'am,': 0.29; 'character': 0.29; 'raise': 0.29; "doesn't": 0.30; 'matching': 0.30; "i'm": 0.30; 'code': 0.31; 'follows': 0.31; 'yields': 0.31; 'there.': 0.32; 'probably': 0.32; 'regular': 0.32; 'quite': 0.32; 'entirely': 0.33; 'maybe': 0.34; 'something': 0.35; 'definition': 0.35; 'received:84': 0.35; 'but': 0.35; 'whilst': 0.36; 'doing': 0.36; 'subject:?': 0.36; 'should': 0.36; 'being': 0.38; 'expected': 0.38; 'minimum': 0.38; 'to:addr:python-list': 0.38; 'previous': 0.38; 'that,': 0.38; 'expect': 0.39; 'sure': 0.39; 'to:addr:python.org': 0.39; 'how': 0.40; 'expression': 0.60; 'negative': 0.60; 'helps': 0.61; 'skip:a 30': 0.61; 'numbers': 0.61; 'times': 0.62; "you've": 0.63; 'show': 0.63; 'maximum': 0.63; 'more': 0.64; '26,': 0.68; 'repeat': 0.74; '2:30': 0.84; 'error;': 0.91 X-CM-Score: 0.00 X-CNFS-Analysis: v=2.1 cv=MtHc6gqe c=1 sm=1 tr=0 a=0nF1XD0wxitMEM03M9B4ZQ==:117 a=0nF1XD0wxitMEM03M9B4ZQ==:17 a=0Bzu9jTXAAAA:8 a=tLkI8qN_j18A:10 a=zwaHAIf4gx4A:10 a=ihvODaAuJD4A:10 a=IkcTkHD0fZMA:10 a=EBOSESyhAAAA:8 a=iC56nj4HAAAA:8 a=5vRN5rKejUUMnfUYFzEA:9 a=QEXdDO2ut3YA:10 a=hHy4X7uaErEA:10 X-AUTH: mrabarnett:2500 Date: Fri, 25 Apr 2014 18:57:23 +0100 From: MRAB User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: python-list@python.org Subject: Re: possible bug in re expression? References: <535A8DB5.4090109@chamonix.reportlab.co.uk> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 74 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1398448647 news.xs4all.nl 2952 [2001:888:2000:d::a6]:47999 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:70608 On 2014-04-25 17:55, Chris Angelico wrote: > On Sat, Apr 26, 2014 at 2:30 AM, Robin Becker wrote: >> Whilst translating some javascript code I find that this >> >> A=re.compile('.{1,+3}').findall(p) >> >> doesn't give any error, but doesn't manage to find the strings in p that I >> want len(A)==>0, the correct translation should have been >> >> A=re.compile('.{1,3}').findall(p) >> >> which works fine. >> >> should >> >> re.compile('.{1,+3}') >> >> raise an error? It doesn't on python 2.7 or 3.3. > > I would say the surprising part is that your js code doesn't mind an > extraneous character in the regex. In a brace like that, negative > numbers have no meaning, so I would expect the definition of the regex > to look for digits, not "anything that can be parsed as a number". So > you've uncovered a bug in your code that just happened to work in js. > > Should it raise an error? Good question. Quite possibly it should, > unless that has some other meaning that I'm not familiar with. Do you > know how it's being interpreted? I'm not entirely sure what you mean > by "len(A)==>0", as ==> isn't an operator in Python or JS. Best way to > continue, I think, would be to use regular expression matching (rather > than findall'ing) and something other than dot, and tabulate input > strings, expected result (match or no match), what JS does, and what > Python does. For instance: > > Regex: "^a{1,3}$" > > "": Not expected, not Python > "a": Expected, Python > "aa": Expected, Python > "aaa": Expected, Python > "aaaa": Not expected, not Python > > Just what we'd expect. Now try the same thing with the plus in there. > I'm finding that none of the above strings yields a match. Maybe > there's something else being matched? > The DEBUG flag helps to show what's happening: >>> r = re.compile('.{1,+3}', flags=re.DEBUG) any None literal 123 literal 49 max_repeat 1 4294967295 literal 44 literal 51 literal 125 When it's parsing the pattern it's doing this: . OK, match any character { Looks like the start of a quantifier 1 OK, the minimum count , OK, the maximum count probably follows + Error; it looks like the '{' was a literal Trying again from the brace: { Literal 1 Literal , Literal + Repeat the previous item one or more times 3 Literal } Literal