code: def _make_mask(self, data, lon_str=LON_STR, lat_str=LAT_STR):
          
          mask = False
          for west, east, south, north in self.mask_bounds:
              if west < east:
                  mask_lon = (data[lon_str] > west) & (data[lon_str] < east)
              else:
                  mask_lon = (data[lon_str] < west) | (data[lon_str] > east)
              mask_lat = (data[lat_str] > south) & (data[lat_str] < north)
              mask |= mask_lon & mask_lat
          return mask
docs: Construct the mask that defines a region on a given data's grid.