code: def _seconds_as_string(seconds):
      
      TIME_UNITS = [('s', 60), ('m', 60), ('h', 24), ('d', None)]
      unit_strings = []
      cur = max(int(seconds), 1)
      for suffix, size in TIME_UNITS:
          if size is not None:
              cur, rest = divmod(cur, size)
          else:
              rest = cur
          if rest > 0:
              unit_strings.insert(0, '%d%s' % (rest, suffix))
      return ' '.join(unit_strings)
docs: Returns seconds as a human-friendly string, e.g. '1d 4h 47m 41s'