What's the best way to validate that an IP entered by the user is valid? It comes in as a string.
11 Answers
Don't parse it. Just ask.
import socket
try:
socket.inet_aton(addr)
# legal
except socket.error:
# Not legal
The IPy module (a module designed for dealing with IP addresses) will throw a ValueError exception for invalid addresses.
>>> from IPy import IP
>>> IP('127.0.0.1')
IP('127.0.0.1')
>>> IP('277.0.0.1')
Traceback (most recent call last):
...
ValueError: '277.0.0.1': single byte must be 0 <= byte < 256
>>> IP('foobar')
Traceback (most recent call last):
...
ValueError: invalid literal for long() with base 10: 'foobar'
However, like Dustin's answer, it will accept things like "4" and "192.168" since, as mentioned, these are valid representations of IP addresses.
If you're using Python 3.3 or later, it now includes the ipaddress module:
>>> import ipaddress
>>> ipaddress.ip_address('127.0.0.1')
IPv4Address('127.0.0.1')
>>> ipaddress.ip_address('277.0.0.1')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.3/ipaddress.py", line 54, in ip_address
address)
ValueError: '277.0.0.1' does not appear to be an IPv4 or IPv6 address
>>> ipaddress.ip_address('foobar')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.3/ipaddress.py", line 54, in ip_address
address)
ValueError: 'foobar' does not appear to be an IPv4 or IPv6 address
For Python 2, you can get the same functionality using ipaddress if you install python-ipaddress:
pip install ipaddress
This module is compatible with Python 2 and provides a very similar API to that of the ipaddress module included in the Python Standard Library since Python 3.3. More details here. In Python 2 you will need to explicitly convert the IP address string to unicode: ipaddress.ip_address(u'127.0.0.1').
def is_valid_ip(ip):
"""Validates IP addresses.
"""
return is_valid_ipv4(ip) or is_valid_ipv6(ip)
IPv4:
def is_valid_ipv4(ip):
"""Validates IPv4 addresses.
"""
pattern = re.compile(r"""
^
(?:
# Dotted variants:
(?:
# Decimal 1-255 (no leading 0's)
[3-9]\d?|2(?:5[0-5]|[0-4]?\d)?|1\d{0,2}
|
0x0*[0-9a-f]{1,2} # Hexadecimal 0x0 - 0xFF (possible leading 0's)
|
0+[1-3]?[0-7]{0,2} # Octal 0 - 0377 (possible leading 0's)
)
(?: # Repeat 0-3 times, separated by a dot
\.
(?:
[3-9]\d?|2(?:5[0-5]|[0-4]?\d)?|1\d{0,2}
|
0x0*[0-9a-f]{1,2}
|
0+[1-3]?[0-7]{0,2}
)
){0,3}
|
0x0*[0-9a-f]{1,8} # Hexadecimal notation, 0x0 - 0xffffffff
|
0+[0-3]?[0-7]{0,10} # Octal notation, 0 - 037777777777
|
# Decimal notation, 1-4294967295:
429496729[0-5]|42949672[0-8]\d|4294967[01]\d\d|429496[0-6]\d{3}|
42949[0-5]\d{4}|4294[0-8]\d{5}|429[0-3]\d{6}|42[0-8]\d{7}|
4[01]\d{8}|[1-3]\d{0,9}|[4-9]\d{0,8}
)
$
""", re.VERBOSE | re.IGNORECASE)
return pattern.match(ip) is not None
IPv6:
def is_valid_ipv6(ip):
"""Validates IPv6 addresses.
"""
pattern = re.compile(r"""
^
\s* # Leading whitespace
(?!.*::.*::) # Only a single whildcard allowed
(?:(?!:)|:(?=:)) # Colon iff it would be part of a wildcard
(?: # Repeat 6 times:
[0-9a-f]{0,4} # A group of at most four hexadecimal digits
(?:(?<=::)|(?<!::):) # Colon unless preceeded by wildcard
){6} #
(?: # Either
[0-9a-f]{0,4} # Another group
(?:(?<=::)|(?<!::):) # Colon unless preceeded by wildcard
[0-9a-f]{0,4} # Last group
(?: (?<=::) # Colon iff preceeded by exacly one colon
| (?<!:) #
| (?<=:) (?<!::) : #
) # OR
| # A v4 address with NO leading zeros
(?:25[0-4]|2[0-4]\d|1\d\d|[1-9]?\d)
(?: \.
(?:25[0-4]|2[0-4]\d|1\d\d|[1-9]?\d)
){3}
)
\s* # Trailing whitespace
$
""", re.VERBOSE | re.IGNORECASE | re.DOTALL)
return pattern.match(ip) is not None
The IPv6 version uses "(?:(?<=::)|(?<!::):)", which could be replaced with "(?(?<!::):)" on regex engines that support conditionals with look-arounds. (i.e. PCRE, .NET)
Edit:
- Dropped the native variant.
- Expanded the regex to comply with the RFC.
- Added another regex for IPv6 addresses.
Edit2:
I found some links discussing how to parse IPv6 addresses with regex:
- A Regular Expression for IPv6 Addresses - InterMapper Forums
- Working IPv6 regular expression - Patrick’s playground blog
- test-ipv6-regex.pl - Perl script with tons of test-cases. It seems my regex fails on a few of those tests.
Edit3:
Finally managed to write a pattern that passes all tests, and that I am also happy with.
I think this would do it...
def validIP(address):
parts = address.split(".")
if len(parts) != 4:
return False
for item in parts:
if not 0 <= int(item) <= 255:
return False
return True
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