Changes by Serhiy Storchaka storch...@gmail.com:
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resolution: - not a bug
stage: - resolved
status: open - closed
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue14460
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Serhiy Storchaka added the comment:
Technically this is not a bug.
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nosy: +serhiy.storchaka
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue14460
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Matthew Barnett added the comment:
Lookarounds can contain capture groups:
import re
re.search(r'a(?=(.))', 'ab').groups()
('b',)
re.search(r'(?=(.))b', 'ab').groups()
('a',)
so lookarounds that are optional or can have no repeats might have a use.
I'm not sure whether it's useful to
py.user added the comment:
m = re.search(r'(?=(a)){10}bc', 'abc', re.DEBUG)
max_repeat 10 10
assert -1
subpattern 1
literal 97
literal 98
literal 99
m.group()
'bc'
m.groups()
('a',)
It works like there are 10 letters a before letter b.
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Matthew Barnett added the comment:
Lookarounds can capture, but they don't consume. That lookbehind is matching
the same part of the string every time.
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue14460
Tim Peters added the comment:
I would not call this a bug - it's just usually a silly thing to do ;-)
Note, e.g., that p{N} is shorthand for writing p N times. For example, p{4} is
much the same as (but not exactly so in all cases; e.g., if `p` happens to
contain a capturing group, the
py.user added the comment:
Tim Peters wrote:
(?=a)(?=a)(?=a)(?=a)
There are four different points.
If a1 before a2 and a2 before a3 and a3 before a4 and a4 before something.
Otherwise repetition of assertion has no sense. If it has no sense, there
should be an exception.
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Tim Peters added the comment:
(?=a)(?=a)(?=a)(?=a)
There are four different points.
If a1 before a2 and a2 before a3 and a3 before a4 and a4
before something.
Sorry, that view doesn't make any sense. A successful lookbehind assertion
matches the empty string. Same as the regexp
Tim Peters added the comment:
BTW, note that the idea successful lookaround assertions match an empty
string isn't just a figure of speech: it's the literal truth, and - indeed -
is key to understanding what happens here. You can see this by adding some
capturing groups around the
py.user added the comment:
Tim Peters wrote:
Should that raise an exception?
i += 0
(?=a)b
(?=a)a
These are another cases. The first is very special. The second and third are
special too, but with different contents of assertion they can do useful work.
While (?=any contents){N}a never
Mark Lawrence added the comment:
Can someone comment on this regex problem please, they're just not my cup of
tea.
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nosy: +BreamoreBoy
versions: +Python 2.7, Python 3.4, Python 3.5 -Python 3.2
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Python tracker rep...@bugs.python.org
New submission from py.user port...@yandex.ru:
import re
re.search(r'(?=a){100,200}bc', 'abc', re.DEBUG)
max_repeat 100 200
assert -1
literal 97
literal 98
literal 99
_sre.SRE_Match object at 0xb7429f38
re.search(r'(?=a){100,200}bc', 'abc', re.DEBUG).group()
'bc'
I expected
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