docs: def str_rate(self):
          """Returns the rate with formatting."""
          # Handle special cases.
          if not self._eta.started or self._eta.stalled or not self.rate:
              return '--- KiB/s'
  
          unit_rate, unit = UnitByte(self.rate).auto_no_thousands
          if unit_rate >= 10:
              formatter = '%d'
          else:
              formatter = '%0.1f'
          return '{0} {1}/s'.format(locale.format(formatter, unit_rate, grouping=False), unit)