from random import SystemRandom


def random_token(length, byte_filter):
    allowed_bytes = "".join(c for c in map(chr, range(128)) if byte_filter(c))
    random = SystemRandom()
    return "".join([random.choice(allowed_bytes) for _ in range(length)])


def alpha_numeric(length):
    return random_token(length, str.isalnum)


def lower_case(length):
    return random_token(length, str.islower)