docs: def report_totals(bytes_in, bytes_out, nag_about_gifs, errors):
      """Report the total number and percent of bytes saved."""
      if bytes_in:
          bytes_saved = bytes_in - bytes_out
          percent_bytes_saved = bytes_saved / bytes_in * 100
          msg = ''
          if Settings.test:
              if percent_bytes_saved > 0:
                  msg += "Could save"
              elif percent_bytes_saved == 0:
                  msg += "Could even out for"
              else:
                  msg += "Could lose"
          else:
              if percent_bytes_saved > 0:
                  msg += "Saved"
              elif percent_bytes_saved == 0:
                  msg += "Evened out"
              else:
                  msg = "Lost"
          msg += " a total of {} or {:.{prec}f}%".format(
              _humanize_bytes(bytes_saved), percent_bytes_saved, prec=2)
          if Settings.verbose:
              print(msg)
              if Settings.test:
                  print("Test run did not change any files.")
  
      else:
          if Settings.verbose:
              print("Didn't optimize any files.")
  
      if nag_about_gifs and Settings.verbose:
          print("Most animated GIFS would be better off converted to"
                " HTML5 video")
  
      if not errors:
          return
  
      print("Errors with the following files:")
      for error in errors:
          print("{}: {}".format(error[0], error[1]))