def image_path_from_index(self, index):
        """
        given image index, find out full path
        :param index: index of a specific image
        :return: full path of this image
        """
        image_file = os.path.join(self.data_path, 'JPEGImages', index + '.jpg')
        assert os.path.exists(image_file), 'Path does not exist: {}'.format(image_file)
        return image_file

        given image index, find out full path
        :param index: index of a specific image
        :return: full path of this image
        
lib/dataset/pascal_voc.py