Python regex not matching but works on regex tester

Question

import re as regex
pattern = regex.compile(r'\w[\w\/\\-]*(\s*[\w\/\\-])*')
print pattern.findall("HELLO-WORLD")

This just prints out ['']

The regex works correctly on an online regex tester. Why is it not matching?

If I would put my regex \w[\w\/\\-]*(\s*[\w\/\\-])* on regex101.com it works fine and matches HELLO-WORLD as expected. — user1410668
– user1410668, Commented Jun 8, 2016 at 20:09
@alexis: There is no lookahead in my suggested pattern, please see the answer. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 8, 2016 at 20:17

Wiktor Stribiżew · Accepted Answer · 2016-06-08 20:14:10Z

1

You can use a non-capturing group (i.e. (?:\s*[\w/\\-]), the (?:...) does not form a capturing group and re.findall returns the whole match, not the captured group value(s)):

import re
pattern = re.compile(r'\w[\w/\\-]*(?:\s*[\w/\\-])*')
print(pattern.findall("HELLO-WORLD"))

See the IDEONE demo

Also, note that / symbol does not have to be escaped in a Python regex pattern.

Another point is that there is a PyPi regex module, and that is why I suggest using import re rather than hiding it with as regex.

answered Jun 8, 2016 at 20:14

Wiktor Stribiżew

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3 Comments

user1410668 Over a year ago

This is perfect. Thank you.

alexis Over a year ago

Explanation: if re.findall contains capturing groups, it will only return the content captured by the groups; not the whole match.

Wiktor Stribiżew Over a year ago

Yes, here is the relevant link: docs.python.org/2/library/re.html#re.findall

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