docs: def make_unique_str(num_chars=20):
      """make a random string of characters for a temp filename"""
      chars = 'abcdefghigklmnopqrstuvwxyz'
      all_chars = chars + chars.upper() + '01234567890'
      picks = list(all_chars)
      return ''.join([choice(picks) for i in range(num_chars)])