Regex search not working

Question

I wrote a function that verifies if a specific pattern exists in a given string:

import re
def has_pattern(string, regex):
    if string and re.compile(regex).search(string) is not None:
        return True
    return False

but for some reason my test doesn't show the expected result:

# for absolute path on windows
pattern = '^[a-zA-Z]:\\\\[^\\\\]' # actual regex: [a-zA-Z]:\\[^\\]
path = 'a:\\' # for this result should be 'True'
print('Pattern: \'{0}\''.format(pattern))
print('Result: {0}'.format(has_pattern(path, pattern)))

Your regex is _requiring_ another non-\ character after the first \. Try a negative lookahead instead. — tobias_k, Feb 10 '16 at 10:33
You have not specified what type of strings you want to match, just one example. There can be a ton of regexps that we can offer, but they might not work with other strings you have. — Wiktor Stribiżew, Feb 10 '16 at 10:36
Okay, it's supposed to use regular strings, not raw strings for example. — neuronalbit, Feb 10 '16 at 10:37
@WiktorStribiżew I think his requirements are clear. The question is about why the test string doesn't validate. — Matthew, Feb 10 '16 at 10:38

Matthew · Accepted Answer · 2016-02-10T11:22:47.870

2

Your pattern is looking for a letter (upper or lowercase) at the beginning of the string followed by a colon, a backslash, and then another character which is not a backslash.

Your testing input does not end in this non-backslash character, thus does not match the pattern.

One possible pattern adaption would be:

regex: ^[a-zA-Z]:\\(?:$|[^\\])
formatted for python string: ^[a-zA-Z]:\\\\(?:$|[^\\\\])

edited Feb 10 '16 at 11:22

answered Feb 10 '16 at 10:33

Matthew

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I misinterpreted the output of my used [regex-checker](https://regex101.com/). But thanks anyway :) – neuronalbit Feb 10 '16 at 10:36
Explaining that is not a solution. regex101.com can do that, too. – Wiktor Stribiżew Feb 10 '16 at 10:36
How is this not a solution? He asked about why his regex wasn't validating the given input. This is the reason why. – Matthew Feb 10 '16 at 10:37
Then it is a dupe of [What does the regex mean](http://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean). – Wiktor Stribiżew Feb 10 '16 at 10:38
@WiktorStribiżew So obviously referring to a `Regex`-Guide makes my question a duplicate, why is that? Please state the exact location that involves this particular problem? – neuronalbit Feb 10 '16 at 10:54
There is a whole section devoted to online regex testers. Choose [regex101.com](http://regex101.com), it will tell you all about your regex. – Wiktor Stribiżew Feb 10 '16 at 11:02

Regex search not working

1 Answers1