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)