small function to check if a string is yubikey or not just based on length and if all chars are in the modhex

isyubikey.py

def isYubikey(string):
    """
    Checks if a string looks like a yubikey.
    Yubikey strings are exactly 44 characters and use modhex
    """
    modhex = "cbdefghijklnrtuv"
    if len(string) != 44:
        return False
    for i in string:
        if i not in modhex:
            return False
    return True