regular expression negate a word (not character)

[Summercool]

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

[Summercool]

On Jan 25, 5:16 pm, Summercool <[e-mail]:

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

i could think of something like

/[^s][^n][^o][^w]\s*tire/i

but what if it is not snow but some 20 character-word, then do we need
to do it 20 times to negate it? any shorter way?

[Ben Morrow]

[newsgroups line fixed, f'ups set to clpm]

Quoth Summercool <Su************@gmail.com>:

On Jan 25, 5:16 pm, Summercool <[e-mail]:

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

i could think of something like

/[^s][^n][^o][^w]\s*tire/i

but what if it is not snow but some 20 character-word, then do we need
to do it 20 times to negate it? any shorter way?

This is no good, since 'snoo tire' fails to match even though you want
it to. You need something more like

/ (?: [^s]... | [^n].. | [^o]. | [^w] | ^ ) \s* tire /ix

but that gets *really* tedious for long strings, unless you generate it.

Ben

[Summercool]

to add to the test cases, the regular expression must be able to grep
snowbird tire
tired on a snow day
snow tire and regular tire

[bearophileHUGS]

Summercool:

to add to the test cases, the regular expression must be able to grep
snow tire and regular tire

I presume there only the second tire has to be found.

This is my first try:

text = """
tire
word tire word
word retire word
word tired word
snowbird tire word
tired on a snow day word
snow tire and regular tire word
word snow tire word
word snow tire word
word some snowtires word
"""

import re

def finder(text):
patt = re.compile( r"\b (\w*) \s* (tire)", re.VERBOSE)
for mo in patt.finditer(text):
if not mo.group(1).endswith("snow"):
yield mo.start(2)

for end in finder(text):
print end

The (lazy) output is the starting point of the "tire" that match:
1
11
28
43
63
73
120

Bye,
bearophile

[Paddy]

On Jan 26, 1:16 am, Summercool <[e-mail]:

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

Try the answer here:
http://mail.python.org/pipermail/tut...st/024902.html

[bearophileHUGS]

Paddy:

Try the answer here:
http://mail.python.org/pipermail/tut...st/024902.html

But in the OP problem there can be variable-sized spaces in the
middle...

Bye,
bearophile

[Ilya Zakharevich]

[A complimentary Cc of this posting was sent to
Summercool
<Su************@gmail.com>], who wrote in article <27**********************************@n20g2000hsh. googlegroups.com>:

so for example, it will grep for

winter tire
tire
retire
tired

but will not grep for

snow tire
snow tire
some snowtires

This does not describe the problem completely. What about

thisnow tire
snow; tire

etc? Anyway, one of the obvious modifications of

(^ | \b(?!snow) \w+ ) \W* tire

should work.

Hope this helps,
Ilya

[Paul McGuire]

On Jan 25, 7:16*pm, Summercool <[e-mail]:

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

Too bad pyparsing's not an option. Here's what it would look like:

data = """
Match:

winter tire
tire
retire
tired

But not match:

snow tire
snow tire
some snowtires

snowbird tire
tired on a snow day
snow tire and regular tire

"""

from pyparsing import CaselessLiteral,Literal,line

# caseless wasn't really necessary but you never know
# when you'll run into a "Snow tire"
snow = CaselessLiteral("snow")
tire = Literal("tire")
tire.ignore(snow + tire)

for matchTokens,matchStart,matchEnd in tire.scanString(data):
print line(matchStart, data)
Prints:

winter tire
tire
retire
tired

snowbird tire
tired on a snow day
snow tire and regular tire

-- Paul