code: def prune_zero_padding(gt_box, gt_label, difficult=None):
      valid_cnt = 0
      for i in range(len(gt_box)):
          if (gt_box[i] == 0).all():
              break
          valid_cnt += 1
      return (
          gt_box[:valid_cnt],
          gt_label[:valid_cnt],
          difficult[:valid_cnt] if difficult is not None else None,
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  import os
  import sys
  import numpy
  import itertools
  import paddle
  from ppdet.modeling.rbox_utils import poly2rbox_np
  from ppdet.utils.logger import setup_logger
label_desc: Use image node_id 5 for calling a global function with example usage: prune_zero_padding(gt_box, gt_label, difficult) and returns: gt_box,  gt_label,  unknown