code: def transition_effect(self, index, event_time, population_view):
          
          population_view.update(pd.Series(self.state_id, index=index))
          self._transition_side_effect(index, event_time)
docs: Updates the simulation state and triggers any side-effects associated with entering this state.
  
          Parameters
          ----------
          index : iterable of ints
              An iterable of integer labels for the simulants.
          event_time : pandas.Timestamp
              The time at which this transition occurs.
          population_view : `vivarium.framework.population.PopulationView`
              A view of the internal state of the simulation.