Verifying IP address using regex in Python

Question

I am trying to validate an IP address. Following is the code. Can anyone please tell me what is wrong in the code?

import re

ip = '355.4'

m = re.match('^((?:1?\d{0,2}|2[0-4]\d{1}|25[0-5]).){3}(?:1?\d{0,2}|2[0-4]\d{1}|25[0-5])$', ip)
if m:
    print "correct"
    print m.groups()
else:
    print "wrong"

According to the IP given, it should print wrong as output but it prints correct ('4',) as the output.

Possibly interesting: if you want help debugging the regex, I've thrown it into a visualizer. It may be of help now, or in the future! — Martijn Arts
– Martijn Arts, Commented Mar 11, 2015 at 11:42

ajay_t · Accepted Answer · 2015-03-11 12:56:21Z

2

If you are allowed to not to use regex, you can use python's socket package . inet_aton("string") converts the string to ip address,if this is not valid ip then it will throw exception.

Simple example I have tried:

    import socket

    def check_valid(address):
        try:
            socket.inet_aton(address)
            return address.count('.') == 3
        except socket.error:
            return False

    if __name__ == "__main__":
        print check_valid("192.168.1.255")

It will check all valid ip address like 192.168.1.257 is invalid while 192.168.1.255 is valid.

edited Mar 11, 2015 at 12:56

answered Mar 11, 2015 at 11:57

ajay_t

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Comments

Vipul · Accepted Answer · 2015-03-11 11:40:00Z

0

I was making a mistake by not giving \ before . which was resulting in it matching any character.

import re

ip = '255.25.2.256'

m = re.match('^((?:1?\d{0,2}|2[0-4]\d{1}|25[0-5])\.){3}(?:1?\d{0,2}|2[0-4]\d{1}|25[0-5])$', ip)
if m:
    print "correct"
    print m.groups()
else:
    print "wrong"

answered Mar 11, 2015 at 11:40

Vipul

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Comments

iced · Accepted Answer · 2015-03-11 11:45:43Z

0

len(ip.split(".")) == 4 and all(map(lambda o: o.isdigit() and int(o) <= 255, ip.split(".")))

Never ever use regexps in code. Please.

answered Mar 11, 2015 at 11:45

iced

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13 Comments

deceze Over a year ago

I wouldn't say "never", but certainly not for a problem such as this. +1

Vipul Over a year ago

Why shouldn't I use regex?

iced Over a year ago

because they are unreadable. it's write-only stuff. it's ok to use them in editor or in shell - for 1-time use (which I'm doing dozens times per day e.g.), but not in code.

Padraic Cunningham Over a year ago

You should also not repeat yourself, you are splitting twice just to put it all into one line.

Padraic Cunningham Over a year ago

@iced, the is the point, not everything can or should be a single line of code. Also regex has it's uses in code so saying to never use it is simply wrong

|

Jims · Accepted Answer · 2015-03-11 11:58:51Z

0

You should remove the optionnal quantifier ? in :1?. Otherwise .... is a valid ip address.

answered Mar 11, 2015 at 11:58

Jims

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