Validating a uuid4 with Python.

validate_uuid4.py

from uuid import UUID

def validate_uuid4(uuid_string):

    """
    Validate that a UUID string is in
    fact a valid uuid4.

    Happily, the uuid module does the actual
    checking for us.

    It is vital that the 'version' kwarg be passed
    to the UUID() call, otherwise any 32-character
    hex string is considered valid.
    """

    try:
        val = UUID(uuid_string, version=4)
    except ValueError:
        # If it's a value error, then the string 
        # is not a valid hex code for a UUID.
        return False

    # If the uuid_string is a valid hex code, 
    # but an invalid uuid4,
    # the UUID.__init__ will convert it to a 
    # valid uuid4. This is bad for validation purposes.

    return val.hex == uuid_string

if __name__ == '__main__':

    # Valid uuid, generated by uuid4():
    x = '89eb35868a8247a4a911758a62601cf7'
    print validate_uuid4(x)

    # Same as above, except for the 17th charecter
    # which is a valid hex string, but not a valid uuid4.
    x = '89eb35868a8247a4c911758a62601cf7'
    print validate_uuid4(x)

A ValueError is not the only type of exception UUID can throw. For example, if you try UUID(0), it will produce an AttributeError. Assuming you want the function to return False in this case (since 0 is clearly not a valid UUID4), you could consider replace except ValueError with except Exception.

@khpeek you are right but in his function he explicitly expects a string

I think val == UUID(uuid_string) would work the best. No need to get .hex() or do any string replacements. The reason to use UUID(uuid_string) without the version kwarg is so it would work with the other formats UUID allows too like curly braces and urn prefixes. These extraneous parts of the string are removed by UUID.init().

val is possibly converted to uuid4.
UUID(uuid_string) is just the hex string as is with no conversion.

I guess this gist just expects only hex strings as input.

I would just replace the return val.hex == uuid_string with return str(val) == uuid_string

would it make sense to .lower() the string before comparing it? (just in case)

@apostolos Sure, validators typical tell you whether and object passes some criteria; cleaning or scrubbing your inputs is where you massage things to give the user a break on things like capitalization. Then you validate the massaged version.