code: def _update_time(self):
          
          self.time['steps'] += 1
          # time in days since beginning
          self.time['days_elapsed'] += self.time['timestep'] / const.seconds_per_day
          if self.time['day_of_year_index'] >= self.time['num_steps_per_year']-1:
              self._do_new_calendar_year()
          else:
              self.time['day_of_year_index'] += 1
docs: Increments the timestep counter by one.
  
          Furthermore ``self.time['days_elapsed']`` and
          ``self.time['num_steps_per_year']`` are updated.
  
          The function is called by the time stepping methods.