Regular expression 4 matching IP adresses

Question

Hey, guys, have a little question. How to correctly match an ip address with regular expression? I have tried by myself, but something went wrong. Here's my code:

import re
ipfilter = r"^(([01])?([0-9])?[0-9]|2[0-4][0-9]|25[0-5]\.){3}(([01])?([1-9])?[0-9]|2[0-4][0-9]|25[0-5])

Answer 1

You could shortened your regular expression as this:

ipfilter = r"^((25[0-5]|2[0-4]\d|[01]?\d\d?)(\.(?!$)|$)){4}quot;

Answer 2

Hi, in the first part of regex you should separate the number match from dot match otherwise the rule can't matching the number/dot repetition
Fix the regex simply by adding a parenthesis before \.

^((([01])?([0-9])?[0-9]|2[0-4][0-9]|25[0-5])\.){3}(([01])?([1-9])?[0-9]|2[0-4][0-9]|25[0-5])$

the IP with 255 was captured by the second part of your regex.

Answer 3

Not sure: I recently discover it in a code... I can only suppose that (\.(?!$)|$) should be interpreted as 'dot authorized if not last char' ('dot if not last char or nothing')

Answer 4

Thank you for a great answer, that really helps!

Answer 5

visph, can you explain (?!$) group?