code: def _keys_from_label(self, label):
          '''Convert a label into a kvl key.
          '''
          k1 = (label.content_id1, label.content_id2,
                label.annotator_id, time_complement(label.epoch_ticks))
          k2 = (label.content_id2, label.content_id1,
                label.annotator_id, time_complement(label.epoch_ticks))
          return k1, kf _keys_from_label(self, label):
          '''Convert a label into a kvl key.
          '''
          k1 = (label.content_id1, label.content_id2,
                label.annotator_id, time_complement(label.epoch_ticks))
          k2 = (label.content_id2, label.content_id1,
                label.annotator_id, time_complement(label.epoch_ticks))
          return k1, k2
docs: Convert a label into a kvl key.