code: def _get_frameshift_start(self, variant_data):
          
  
          if DBG:
              print("is_frameshift:{}".format(variant_data.is_frameshift))
              print("variant_start_aa:{}".format(variant_data.variant_start_aa))
          if variant_data.is_frameshift:
              variant_data.frameshift_start = variant_data.variant_start_aa
          return variant_data
docs: Get starting position (AA ref index) of the last frameshift
          which affects the rest of the sequence, i.e. not offset by subsequent frameshifts
          :param variant_data: info on each variant
          :type variant_data: attrs
          :return variant data with additional field for AA index (1-based) of the frameshift start
          :rtype attrs