def image_path_from_index(self, index):
        """
        Construct an image path from the image's "index" identifier.
        """
        image_path = os.path.join(self._data_path, 'Data', self._image_set, index + self._image_ext[0])
        assert os.path.exists(image_path), 'path does not exist: {}'.format(image_path)
        return image_path

        Construct an image path from the image's "index" identifier.
        
lib/datasets/imagenet.py