code: def set_quality_index(self):
          
          window_start = self.parent.value('window_start')
          window_length = self.parent.value('window_length')
          qual = self.annot.get_stage_for_epoch(window_start, window_length,
                                                attr='quality')
          #lg.info('winstart: ' + str(window_start) + ', quality: ' + str(qual))
  
          if qual is None:
              self.idx_quality.setCurrentIndex(-1)
          else:
              self.idx_quality.setCurrentIndex(QUALIFIERS.index(qual))
docs: Set the current signal quality in combobox.