def _print_speed(self):
        '''Print the current speed.'''
        if self._bandwidth_meter.num_samples:
            speed = self._bandwidth_meter.speed()

            if self._human_format:
                file_size_str = wpull.string.format_size(speed)
            else:
                file_size_str = '{:.1f} b'.format(speed * 8)

            speed_str = _('{preformatted_file_size}/s').format(
                preformatted_file_size=file_size_str
            )
        else:
            speed_str = _('-- B/s')

        self._print(speed_str)
Print the current speed.