python regex "negative lookahead assertions" problems
python at mrabarnett.plus.com
Sun Nov 22 17:32:49 CET 2009
Tim Chase wrote:
>>>>> import re
>>>>> line='2009-11-22 12:15:441 lmqkjsfmlqshvquhsudfhqf qlsfh
>>>>> qsduidfhqlsiufh qlsiuf qldsfhqlsifhqlius dfh warning qlsfj lqshf
>>>>> lqsuhf lqksjfhqisudfh qiusdfhq iusfh'
>> <_sre.SRE_Match object at 0xb75b1598>
>> I would expect that this would NOT match as it's a negative lookahead
>> and warning is in the string.
> This first finds everything (".*") and then asserts that "warning"
> doesn't follow it, which is correct in your example. You may have to
> assert that "warning" doesn't exist at every point along the way:
> which will match up-to-but-not-including the "warning" text. If you
> don't want it at all, you'd have to also anchor the far end
> but in the 2nd case I'd just as soon invert the test:
> if 'warning' not in line:
The trick is to think what positive lookahead you'd need if you wanted
check whether 'warning' is present:
and then negate it:
More information about the Python-list