code: def add_lv_grid_district(self, lv_grid_district):
          # TODO: check docstring
          
  
          if lv_grid_district not in self._lv_grid_districts and \
                  isinstance(lv_grid_district, LVGridDistrictDing0):
              self._lv_grid_districts.append(lv_grid_district)
docs: Adds a LV grid district to _lv_grid_districts if not already existing
          
          Args
          ----
          lv_grid_district: :shapely:`Shapely Polygon object<polygons>`
              Descr