code: def set_timestep(self, timestep=const.seconds_per_day, num_steps_per_year=None):
          
          if num_steps_per_year is not None:
              timestep = const.seconds_per_year / num_steps_per_year
          # Need a more sensible approach for annual cycle stuff
          self.timestep = timestep
docs: Calculates the timestep in unit seconds
          and calls the setter function of :func:`timestep`
  
          :param float timestep:              the amount of time over which
                                              :func:`step_forward` is integrating
                                              in unit seconds [default: 24*60*60]
          :param float num_steps_per_year:    a number of steps per calendar year
                                              (optional)
  
          If the parameter *num_steps_per_year* is specified and not ``None``,
          the timestep is calculated accordingly and therefore the given input
          parameter *timestep* is ignored.