docs: def string_range(last):
      """Compute the range of string between "a" and last.
  
      This works for simple "a to z" lists, but also for "a to zz" lists.
      """
      for k in range(len(last)):
          for x in product(string.ascii_lowercase, repeat=k+1):
              result = ''.join(x)
              yield result
              if result == last:
                  return