code: def _guessunit(self):
          
          if not self.days % 1:
              return 'd'
          elif not self.hours % 1:
              return 'h'
          elif not self.minutes % 1:
              return 'm'
          elif not self.seconds % 1:
              return 's'
          else:
              raise ValueError(
                  'The stepsize is not a multiple of one '
                  'second, which is not allowed.')
docs: Guess the unit of the period as the largest one, which results in
          an integer duration.