Regexp To Check If An Ip Is Valid

January 30, 2024 Post a Comment

I'm wondering if it's possible to compare values in regexps with the regexp system in Python. Matching the pattern of an IP is easy, but each 1-3 digits cannot be above 255 and tha

Solution 1:

No need for regular expressions here. Some background:

>>> import socket
>>> socket.inet_aton('255.255.255.255')'\xff\xff\xff\xff'
>>> socket.inet_aton('255.255.255.256')
Traceback (most recent call last):
  File "<input>", line 1, in <module>
error: illegal IP address string passed to inet_aton
>>> socket.inet_aton('my name is nobody')
Traceback (most recent call last):
  File "<input>", line 1, in <module>
error: illegal IP address string passed to inet_aton

So:

import socket

defip_address_is_valid(address):
    try: socket.inet_aton(address)
    except socket.error: returnFalseelse: returnTrue

Note that addresses like '127.1' could be acceptable on your machine (there are systems, including MS Windows and Linux, where missing octets are interpreted as zero, so '127.1' is equivalent to '127.0.0.1', and '10.1.4' is equivalent to '10.1.0.4'). Should you require that there are always 4 octets, change the last line from:

else: return True

into:

else: return address.count('.') == 3

Solution 2:

You need to check the allowed numbers in each position. For the first optional digit, acceptable values are 0-2. For the second, 0-5 (if the first digit for that part is present, otherwise 0-9), and 0-9 for the third.

I found this annotated example at http://www.regular-expressions.info/regexbuddy/ipaccurate.html :

\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

Solution 3:

You can check a 4-octet IP address easily without regexes at all. Here's a tested working method:

>>>defvalid_ip(ip):...   parts = ip.split('.')...return (...len(parts) == 4...andall(part.isdigit() for part in parts)...andall(0 <= int(part) <= 255for part in parts)...       )...>>>valid_ip('1.2.3.4')
True
>>>valid_ip('1.2.3.4.5')
False
>>>valid_ip('1.2.   3   .4.5')
False
>>>valid_ip('1.256.3.4.5')
False
>>>valid_ip('1.B.3.4')
False
>>>

Solution 4:

Regex is for pattern matching, but to check for a valid IP, you need to check for the range (i.e. 0 <= n <= 255).

You may use regex to check for range, but that'll be a bit overkill. I think you're better off checking for basic patter and then check for the range for each number.

For example, use the following pattern to match an IP:

([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})

Then check whether each number is within range.

Solution 5:

The following supports IPv4, IPv6 as well as Python 2.7 & 3.3

import socket


defis_valid_ipv4(ip_str):
    """
    Check the validity of an IPv4 address
    """try:
        socket.inet_pton(socket.AF_INET, ip_str)
    except AttributeError:
        try:
            socket.inet_aton(ip_str)
        except socket.error:
            returnFalsereturn ip_str.count('.') == 3except socket.error:
        returnFalsereturnTruedefis_valid_ipv6(ip_str):
    """
    Check the validity of an IPv6 address
    """try:
        socket.inet_pton(socket.AF_INET6, ip_str)
    except socket.error:
        returnFalsereturnTruedefis_valid_ip(ip_str):
    """
    Check the validity of an IP address
    """return is_valid_ipv4(ip_str) or is_valid_ipv6(ip_str)

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