code: def filename(self):
          
          if self._image is not None:
              return self._image.filename
          return 'image.%s' % self.partname.ext
docs: Filename from which this image part was originally created. A generic
          name, e.g. 'image.png', is substituted if no name is available, for
          example when the image was loaded from an unnamed stream. In that
          case a default extension is applied based on the detected MIME type
          of the image.