how to limit input number using ReGex?

Question

I'm trying to use regex and I have a limit for input numbers, I want them to be less or equal to 255:

def validate(ip):
    try:
        x = re.search(r"^(\d+)\.(\d+)\.(\d+)\.(\d+)$", ip.strip())
        for pot in x.groups():
            if int(pot) <= 255:
                return True
            else:
                return False
    except:
         return False
validate('64.128.256.512')

well the problem is when I use a for loop, and using return, it checks only for one group of number (I mean the first one 64) and ignores the other, so the result will be True, but what I expect is False.

For those who don't know, `ReGex` is short for `Re'lar Gexpressions`. — xdhmoore, Sep 02 '22 at 18:55

S.B · Answer 1 · 2022-09-02T19:11:18.367

Because return exits the function. You should first iterate through all the values and check to see if there is an invalid case. This can be done using all() like:

import re

def validate(ip):
    x = re.search(r"^(\d+)\.(\d+)\.(\d+)\.(\d+)$", ip.strip())
    if not x:
        return False

    if all(int(pot) <= 255 for pot in x.groups()):
        return True
    return False

print(validate("64.128.256.512"))
print(validate("64.128.250.212"))
print(validate("foo.128.boo.212"))

output:

False
True
False

Note1: I guess it's an exercise, because there are more robust ways to validate IP addresses. I just fixed the problem you had.

Note2: Since you check for \d in your pattern, you don't need to add that try-except. If another non-digit value is provided, search will give you None and with the check if not x: you can simply return.

score 2 · Accepted Answer · answered Sep 02 '22 at 18:51

2

Regex is overkill here (for a non-robust method of validation) imo~

def validate(ip):
    split_ip = ip.split('.')
    return len(split_ip) == 4 and all(x <= 255 for x in map(int, split_ip))

>>> validate('64.128.256.512')
False
>>> validate('64.128.255.123')
True
>>> validate('64.128.255')
False

answered Sep 02 '22 at 18:51

BeRT2me

12,699
2
13
31

There's a ton that could be added, pos/negative, error catching for alpha characters, more specific ranges pertaining to IPs... etc. But at that point the tried and true regex methods available online from a simple search become better. – BeRT2me Sep 02 '22 at 19:01

score 0 · Answer 3 · answered Sep 02 '22 at 18:48

It seems like you're trying to validate an IP address using regex.

This article covers that.

It suggests using this regex to validate an IPv4 address.
"(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])"

score 0 · Answer 4 · answered Sep 02 '22 at 19:04

the most simple way i founded was:

def validate(ip):
    try:
        x = re.search(r"^(\d+)\.(\d+)\.(\d+)\.(\d+)$", ip.strip()) 
        n = 0
        for pot in x.groups():
            if int(pot) > 255:
                n += 1
        if n != 0:
            return False
        return True
    except:
        return False

how to limit input number using ReGex?

4 Answers4