Python regex matching

Question

I want to extract the string with the following pattern.

MsgTrace(65/26)noop:user=xxx=INBOX:cmd=534

regex should extract noop

but when i try the follwong pattern , it extract the string "user" as well.

ImapFetchComplete(56/39)user=xxxxxxxxxx

need to output the word only contains the following pattern.

)somestring:  (it should extract the word somestring)

)somestring=xxxx (this shouldn't be extracted)

#!/usr/bin/python
import os
from subprocess import *
import os
import re

dir="/tmp/logs/"
os.chdir(dir)
for filename in os.listdir(dir):
    with open(filename) as fp:
        for line in fp:
             try:
                 print(re.search(r'\)([a-z]*?):',line).group(1))
             except:
                 pass

It does not look like there is a problem with the regex, see regex101.com/r/ImzAyW/1. It cannot match somestring in )somestring=xxxx because there is no :. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 19, 2017 at 9:54
it out put both somestring and somestring= , in the example it output both noop and user=xxxxxxxxxx — Tharanga Abeyseela
– Tharanga Abeyseela, Commented Jan 19, 2017 at 10:02
I think your example is incomplete (because it's behaving as expected, though only by accident). I think you want your match pattern to be r'\)([^:]*?):user=' so that you don't end up picking up the rest of the line. And I think you probably want to be using re.match() instead of re.search() if you're expecting the match to start at the beginning of the string. You'll need to adjust the regex a little more if you use re.match() though. — John Szakmeister
– John Szakmeister, Commented Jan 19, 2017 at 10:09

Tagc · Accepted Answer · 2017-01-19 10:05:55Z

1

Does this do what you want?

import re


def extract_from_string(s):
    match = re.search('(?<=\))\w*?(?=:)', s)
    return match.group(0) if match else None


if __name__ == '__main__':
    s1 = 'MsgTrace(65/26)noop:user=xxx=INBOX:cmd=534'
    s2 = 'ImapFetchComplete(56/39)user=xxxxxxxxxx'
    s3 = 'foo'
    print(extract_from_string(s1))  # 'noop'
    print(extract_from_string(s2))  #  None
    print(extract_from_string(s3))  #  None

edited Jan 19, 2017 at 10:05

answered Jan 19, 2017 at 9:56

Tagc

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2 Comments

Tharanga Abeyseela Over a year ago

if you have both s1,s2 in the log, i need to extract only noop not user=xxxxx

Tagc Over a year ago

@TharangaAbeyseela Gotcha, simple fix. Is this okay now?

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