code: def _quantiles(self):
          
  
          trials = []
          for trial, state in self._trial_state.items():
              if state.last_score is not None and not trial.is_finished():
                  trials.append(trial)
          trials.sort(key=lambda t: self._trial_state[t].last_score)
  
          if len(trials) <= 1:
              return [], []
          else:
              return (trials[:int(math.ceil(len(trials) * PBT_QUANTILE))],
                      trials[int(math.floor(-len(trials) * PBT_QUANTILE)):])
docs: Returns trials in the lower and upper `quantile` of the population.
  
          If there is not enough data to compute this, returns empty lists.