code: def _create_secret(self, length=12):
          
          # Charset will have 64 +- characters
          charset = string.digits + string.ascii_letters + '+-'
          return "".join(random.SystemRandom().choice(charset) for _ in
                  range(length))
docs: Use a cryptograhically-secure Pseudorandom number generator for picking
          a combination of letters, digits, and punctuation to be our secret.
  
          :param length: how long to make the secret (12 seems ok most of the time)