How to determine if a string is a valid v4 UUID?

I'm making a validator based on UUID generated by client browser, I use this to identify a certain type data that the user sends; and would like to validate that the UUID that client sends it is in fact a valid Version 4 UUID.

I found this https://stackoverflow.com/questions/6223185/php-preg-match-uuid-v4, it's close but not exactly what I'm looking for. I wish to know if exists something similar to is_empty() or strtodate() Where if string is not valid Sends FALSE.

I could do based on the regular expression but I would like something more native to test it.

Any ideas?

11/23/2019 EDIT: About the duplicate tag, while the moderator is technicallly correct, this question was formulated with the goal of fibd something else to regex if existed, and in second place this question has become a reference to Pythoners and PHPers and has a different answers/approach to solve the problem and their answers are better explained in general. This is why I consider this question should be perserved

Version 4 UUIDs have the form xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where x is any hexadecimal digit and y is one of 8, 9, A, or B.

^[0-9A-F]{8}-[0-9A-F]{4}-4[0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}$

To allow lowercase letters, use i modifier →

$UUIDv4 = '/^[0-9A-F]{8}-[0-9A-F]{4}-4[0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}$/i';
preg_match($UUIDv4, $value) or die('Not valid UUID');

I found this question while I was looking for a Python answer. To help people in the same situation, I've added the Python solution.

You can use the uuid module:

#!/usr/bin/env python

from uuid import UUID

def is_valid_uuid(uuid_to_test, version=4):
    """
    Check if uuid_to_test is a valid UUID.
    
     Parameters
    ----------
    uuid_to_test : str
    version : {1, 2, 3, 4}
    
     Returns
    -------
    `True` if uuid_to_test is a valid UUID, otherwise `False`.
    
     Examples
    --------
    >>> is_valid_uuid('c9bf9e57-1685-4c89-bafb-ff5af830be8a')
    True
    >>> is_valid_uuid('c9bf9e58')
    False
    """
    
    try:
        uuid_obj = UUID(uuid_to_test, version=version)
    except ValueError:
        return False
    return str(uuid_obj) == uuid_to_test


if __name__ == '__main__':
    import doctest
    doctest.testmod()

All the existing answers use regex. If you're using Python, you might want to consider a try/except in case you don't want to use regex: (Bit shorter than the answer above).

Our validator would then be:

import uuid

def is_valid_uuid(val):
    try:
        uuid.UUID(str(val))
        return True
    except ValueError:
        return False

>>> is_valid_uuid(1)
False
>>> is_valid_uuid("123-UUID-wannabe")
False
>>> is_valid_uuid({"A":"b"})
False
>>> is_valid_uuid([1, 2, 3])
False
>>> is_valid_uuid(uuid.uuid4())
True
>>> is_valid_uuid(str(uuid.uuid4()))
True
>>> is_valid_uuid(uuid.uuid4().hex)
True
>>> is_valid_uuid(uuid.uuid3(uuid.NAMESPACE_DNS, 'example.net'))
True
>>> is_valid_uuid(uuid.uuid5(uuid.NAMESPACE_DNS, 'example.net'))
True
>>> is_valid_uuid("{20f5484b-88ae-49b0-8af0-3a389b4917dd}")
True
>>> is_valid_uuid("20f5484b88ae49b08af03a389b4917dd")
True

import re

UUID_PATTERN = re.compile(r'^[\da-f]{8}-([\da-f]{4}-){3}[\da-f]{12}$', re.IGNORECASE)
uuid = '20f5484b-88ae-49b0-8af0-3a389b4917dd'

if UUID_PATTERN.match(uuid):
    return True
else:
    return False

If you only need it for security (for example if you need to print it in a javascript code and you want to avoid XSS) it doesn't really matter the position of the dashes, so it's just:

 /^[a-f0-9\-]{36}$/i

https://regex101.com/r/MDqB2Z/11

---

(It's not specific for v4, but usually a well written application store them as BINARY(16) after having dropped the dashes, so if something is wrong it will simply not find the object and throw 404, overvalidation may not be needed).