code: def rndstr(size=16, alphabet=""):
      
      rng = random.SystemRandom()
      if not alphabet:
          alphabet = string.ascii_letters[0:52] + string.digits
      return type(alphabet)().join(rng.choice(alphabet) for _ in range(size))
docs: Returns a string of random ascii characters or digits
      :type size: int
      :type alphabet: str
      :param size: The length of the string
      :param alphabet: A string with characters.
      :return: string