[issue19055] Regular expressions: * does not match as many repetitions as possible.
Ezio Melotti added the comment: I agree. -- resolution: - works for me stage: needs patch - resolved status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Serhiy Storchaka added the comment: I think this issue can be closed. Behavior and documentation are correct and match one other. Nothing to do with it. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Changes by Ezio Melotti ezio.melo...@gmail.com: -- assignee: - docs@python components: +Documentation keywords: +easy nosy: +docs@python stage: - needs patch type: behavior - enhancement ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Jason Stumpf added the comment: I like that clearer description. as produce matches is more correct than as possible. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
New submission from Jason Stumpf:
re.match('(a|ab)*',('aba')).group(0)
'a'
According to the documentation, the * should match as many repetitions as
possible. 2 are possible, it matches 1.
Reversing the order of the operands of | changes the behaviour.
re.match('(ab|a)*',('aba')).group(0)
'aba'
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messages: 198116
nosy: Jason.Stumpf
priority: normal
severity: normal
status: open
title: Regular expressions: * does not match as many repetitions as possible.
type: behavior
versions: Python 2.7
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[issue19055] Regular expressions: * does not match as many repetitions as possible.
Changes by Jason Stumpf jstu...@google.com: -- components: +Regular Expressions nosy: +ezio.melotti, mrabarnett ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Changes by David Benbennick dbenb...@gmail.com: -- nosy: +dbenbenn ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Changes by Serhiy Storchaka storch...@gmail.com: -- nosy: +serhiy.storchaka ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Changes by Serhiy Storchaka storch...@gmail.com: -- versions: +Python 3.3, Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
janzert added the comment: The documentation on the | operator in the re module pretty explicitly covers this. http://docs.python.org/2/library/re.html A|B, where A and B can be arbitrary REs, creates a regular expression that will match either A or B. An arbitrary number of REs can be separated by the '|' in this way. This can be used inside groups (see below) as well. As the target string is scanned, REs separated by '|' are tried from left to right. When one pattern completely matches, that branch is accepted. This means that once A matches, B will not be tested further, even if it would produce a longer overall match. In other words, the '|' operator is never greedy. -- nosy: +janzert ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Jason Stumpf added the comment:
Even with the documentation to |, the documentation to * is wrong.
re.match('(a|ab)*c',('abac')).group(0)
'abac'
From the doc: In general, if a string p matches A and another string q matches
B, the string pq will match AB.
Since '(a|ab)*c' matches 'abac', and 'c' matches 'c', that means '(a|ab)*'
matches 'aba'. It does so with 2 repetitions. Thus, in the example from my
initial post, it was not matching with as many repetitions as possible.
I think what you mean is that * attempts to match again after each match of the
preceding regular expression.
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[issue19055] Regular expressions: * does not match as many repetitions as possible.
Jason Stumpf added the comment: Sorry, that implication was backwards. I don't think I can prove from just the documentation that '(a|ab)*' can match 'aba' in certain contexts. If the docs said: * attempts to match again after each match of the preceding regular expression. I think it would describe the observed behaviour. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Matthew Barnett added the comment: The behaviour is correct. Here's a summary of what's happening:- First iteration of the repeated group: Try the first branch. Can match a. Second iteration of the repeated group: Try the first branch. Can't match a. Try the second branch. Can't match ab. Continue with the remainder of the pattern. Can't match c, therefore backtrack to the first iteration of the repeated group: Try the second branch. Can match ab. Second iteration of the repeated group: Try the first branch. Can match a. Third iteration of the repeated group: Try the first branch. Can't match a. Try the second branch. Can't match ab. Continue with the remainder of the pattern. Can match c. Reached the end of the pattern. It has matched abac. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
Jason Stumpf added the comment: I understand what's happening, but that is not what the documentation describes. If the behaviour is correct, the documentation is incorrect. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19055] Regular expressions: * does not match as many repetitions as possible.
R. David Murray added the comment: The documentation is correct and unambiguous. Regular expressions just aren't very intuitive. The documentation says Causes the resulting RE to match 0 or more repetitions of the preceding RE, as many repetitions as are possible. as many repetitions of the preceding RE means that: (a|ab)* is equivalent to (a|ab)(a|ab)(a|ab)... where ... represents add copies of the RE until it doesn't match. Then you have to look at the documentation of '|' to see what it matches, and that documentation (already quoted) explains why the expanded pattern only matches 'a' in 'aba'. Perhaps it would be clearer if it read Causes the RE to be evaluated as if there were zero or more repetitions of the preceding RE, as many repetitions as produce matches? -- nosy: +r.david.murray ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19055 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
