code: def build_grouped_ownership_map(table,
                                  key_from_row,
                                  value_from_row,
                                  group_key):
      
      grouped_rows = groupby(
          group_key,
          sa.select(table.c).execute().fetchall(),
      )
      return {
          key: _build_ownership_map_from_rows(
              rows,
              key_from_row,
              value_from_row,
          )
          for key, rows in grouped_rows.items()
      }
docs: Builds a dict mapping group keys to maps of keys to to lists of
      OwnershipPeriods, from a db table.