docs: def format_progress(i, n):
      """Returns string containing a progress bar, a percentage, etc."""
      if n == 0:
          fraction = 0
      else:
          fraction = float(i)/n
      LEN_BAR = 25
      num_plus = int(round(fraction*LEN_BAR))
      s_plus = '+'*num_plus
      s_point = '.'*(LEN_BAR-num_plus)
      return '[{0!s}{1!s}] {2:d}/{3:d} - {4:.1f}%'.format(s_plus, s_point, i, n, fraction*100)