code: def to_python(self, value):
          
          value = super(BoundingBoxField, self).to_python(value)
          try:
              bbox = gdal.OGRGeometry.from_bbox(value).geos
          except (ValueError, AttributeError):
              return []
          bbox.srid = self.srid
          return bbox
docs: Returns a GEOS Polygon from bounding box values.