New submission from Χρήστος Γεωργίου (Christos Georgiou) <t...@users.sourceforge.net>:
This is based on that StackOverflow answer: http://stackoverflow.com/questions/3957164/3963443#3963443. It also applies to Python 2.6 . Searching for a regular expression that satisfies the mentioned SO question (a regular expression that matches strings with an initial A and/or final Z and returns everything except said initial A and final Z), I discovered something that I consider a bug. I've tried to thoroughly verify that this is not a PEBCAK before reporting the issue here. Given: >>> import re >>> text= 'A***Z' then: >>> re.compile('(?<=^A).*(?=Z$)').search(text).group(0) # regex_1 '***' >>> re.compile('(?<=^A).*').search(text).group(0) # regex_2 '***Z' >>> re.compile('.*(?=Z$)').search(text).group(0) # regex_3 'A***' >>> re.compile('(?<=^A).*(?=Z$)|(?<=^A).*').search(text).group(0) # >>> regex_1|regex_2 '***' >>> re.compile('(?<=^A).*(?=Z$)|.*(?=Z$)').search(text).group(0) # >>> regex_1|regex_3 'A***' >>> re.compile('(?<=^A).*|.*(?=Z$)').search(text).group(0) # regex_2|regex_3 'A***' >>> re.compile('(?<=^A).*(?=Z$)|(?<=^A).*|.*(?=Z$)').search(text).group(0) # >>> regex_1|regex_2|regex_3 'A***' regex_1 returns '***'. Based on the documentation (http://docs.python.org/py3k/library/re.html#regular-expression-syntax), I assert that, likewise, '***' should be returned by: regex_1|regex_2 regex_1|regex_3 regex_1|regex_2|regex_3 And yet, regex_3 ( ".*(?=Z$)" ) seems to take precedence over both regex_1 and regex_2, even though it's the last alternative. This works even if I substitute "(?:regex_n)" for every "regex_n", so it's not a matter of precedence. I really hope that this is a PEBCAK; if that is true, I apologize for any time lost on the issue by anyone; but really don't think it is. ---------- components: Regular Expressions messages: 119088 nosy: tzot priority: normal severity: normal status: open title: regex A|B : both A and B match, but B is wrongly preferred type: behavior versions: Python 3.1 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue10139> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
