New submission from Hendrik Lemelson:
When using the Python 2.7.3 re module, it shows a strange behavior upon the use
of quantifiers together with groups:
>>> re.search('(a*)', 'caaaat').groups()
('',)
>>> re.search('(a+)', 'caaaat').groups()
('aaaa',)
>>> re.search('(a{0,5})', 'caaaat').groups()
('',)
>>> re.search('(a{1,5})', 'caaaat').groups()
('aaaa',)
Whenever a quantifier is used that allows also zero occurrences, the quantifier
loses its greedy behavior. This in my eyes is a defect in the re module. In the
following there is another example with nested groups where the quantifier for
the outer group even prevents the inner groups to match:
>>> re.search('(a(b*)a)', 'caabbaat').groups()
('aa', '')
>>> re.search('(a(b+)a)', 'caabbaat').groups()
('abba', 'bb')
>>> re.search('(a(b*)a){0,1}', 'caabbaat').groups()
(None, None)
>>> re.search('(a(b+)a){0,1}', 'caabbaat').groups()
(None, None)
It would be great if you could manage to fix this.
Thank you in advance.
Regards
Hendrik Lemelson
----------
components: Regular Expressions
messages: 182535
nosy: Hendrik.Lemelson, ezio.melotti, mrabarnett, pitrou
priority: normal
severity: normal
status: open
title: re module shows unexpected non-greedy behavior when using groups
type: behavior
versions: Python 2.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue17257>
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