'Construct an image path from the image\'s "index" identifier.'

def image_path_from_index(self, index):

    file_name = (((('COCO_' + self._data_name) + '_') + str(index).zfill(12)) + '.jpg')
    image_path = osp.join(self._data_path, 'images', self._data_name, file_name)
    assert osp.exists(image_path), 'Path    does    not    exist:    {}'.format(image_path)
    return image_path
