docstr: Return a :class:`~shapely.geometry.polygon.Polygon` instance for
  this image's extents.
docstr_tok: ["Return","a",":","class",":","`","~shapely.geometry.polygon.Polygon","`","instance","for","this","image","'s","extents","."]
code: def bbox(self):
      """
      Return a :class:`~shapely.geometry.polygon.Polygon` instance for
      this image's extents.
  
      """
      if self._bbox is None:
          x0, x1, y0, y1 = self.extent
          self._bbox = sgeom.box(x0, y0, x1, y1)
      return self._bbox
  
imports: import collections
  from pathlib import Path
  import numpy
  from PIL import Image
  import shapely.geometry
label_desc: Use image node_id 4 for calling the Img obj's underlying member method code with example usage: obj.bbox() and returns: self