code: def _random_string():
      
      rng = random.SystemRandom()
      token_value = u''.join(rng.choice(CHARSET) for _ in range(CHAR_GROUPS * CHARS_PER_GROUP))
      if CHARS_PER_GROUP > 1:
          return GROUP_SEP.join(map(u''.join, zip(*[iter(token_value)] * CHARS_PER_GROUP)))
      else:
          return token_value
docs: Generate a globally unique serial / product code of the form ``u'YRAC-EL4X-FQQE-AW4T-WNUV-VN6T'``.
      The generated value is cryptographically strong and has (at least) 114 bits of entropy.
  
      :return: new random string key