code: def compute_evt_params(self):
          ev = self.event
          glob = {k: v.get_value() for k, v in ev['global'].items()}
          params = {k: v[0].get_value() for k, v in ev['local'].items()}
          prep = {k: v[1].get_value() for k, v in ev['local'].items()}
          slopes = {k: v.get_value() for k, v in ev['sw'].items()}
          f1 = ev['f1'].get_value()
          f2 = ev['f2'].get_value()
          if not f2:
              f2 = None
          band = (f1, f2)
          if not (slopes['avg_slope'] or slopes['max_slope']):
              slopes = None
          evt_dat = event_params(self.data, params, band=band, slopes=slopes,
                                 prep=prep, parent=self)
          count = None
          density = None
          if glob['count']:
              count = len(self.data)
          if glob['density']:
              epoch_dur = glob['density_per']
              poi = get_times(self.parent.notes.annot, stage=self.stage,
                              cycle=self.cycle, exclude=True)
              total_dur = sum([x[1] - x[0] for y in poi for x in y['times']])
              density = len(self.data) / (total_dur / epoch_dur)
          return evt_dat, count, density