Summercool said:
somebody who is a regular expression guru... how do you negate a word
and grep for all words that is
tire
but not
snow tire
or
snowtire
so for example, it will grep for
winter tire
tire
retire
tired
but will not grep for
snow tire
snow tire
some snowtires
need to do it in one regular expression
What you want is a negative lookbehind assertion:
<_sre.SRE_Match object at 0x00FCD608>
Unfortunately you want variable whitespace:
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "C:\dev\python\lib\re.py", line 134, in search
return _compile(pattern, flags).search(string)
File "C:\dev\python\lib\re.py", line 233, in _compile
raise error, v # invalid expression
error: look-behind requires fixed-width pattern
Python doesn't support lookbehind assertions that can vary in size. This
doesn't work either:
<_sre.SRE_Match object at 0x00F93480>
Here's some code (not heavily tested) that implements a variable lookbehind
assertion, and a function to mark matches in a string to demonstrate it:
### BEGIN CODE ###
import re
def finditerexcept(pattern,notpattern,string):
for matchobj in
re.finditer('(?:%s)|(?:%s)'%(notpattern,pattern),string):
if not re.match(notpattern,matchobj.group()):
yield matchobj
def markexcept(pattern,notpattern,string):
substrings = []
current = 0
for matchobj in finditerexcept(pattern,notpattern,string):
substrings.append(string[current:matchobj.start()])
substrings.append('[' + matchobj.group() + ']')
current = matchobj.end() #
substrings.append(string[current:])
return ''.join(substrings)
### END CODE ###
.... tire
.... retire
.... tired
.... snow tire
.... snow tire
.... some snowtires
.... '''winter [tire]
[tire]
re[tire]
[tire]d
snow tire
snow tire
some snowtires
--Mark
