code: def pad_box(self, sample, num_max):
      assert "gt_bbox" in sample
      bbox = sample["gt_bbox"]
      gt_num = len(bbox)
      pad_bbox = np.zeros((num_max, 4), dtype=np.float32)
      if gt_num > 0:
          pad_bbox[:gt_num, :] = bbox[:gt_num, :]
      sample["gt_bbox"] = pad_bbox
      if "gt_score" in sample:
          pad_score = np.zeros((num_max,), dtype=np.float32)
          if gt_num > 0:
              pad_score[:gt_num] = sample["gt_score"][:gt_num, 0]
          sample["gt_score"] = pad_score
      if "difficult" in sample:
          pad_diff = np.zeros((num_max,), dtype=np.int32)
          if gt_num > 0:
              pad_diff[:gt_num] = sample["difficult"][:gt_num, 0]
          sample["difficult"] = pad_diff
      if "is_crowd" in sample:
          pad_crowd = np.zeros((num_max,), dtype=np.int32)
          if gt_num > 0:
              pad_crowd[:gt_num] = sample["is_crowd"][:gt_num, 0]
          sample["is_crowd"] = pad_crowd
      if "gt_ide" in sample:
          pad_ide = np.zeros((num_max,), dtype=np.int32)
          if gt_num > 0:
              pad_ide[:gt_num] = sample["gt_ide"][:gt_num, 0]
          sample["gt_ide"] = pad_ide
      return sample
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from numbers import Integral
  import cv2
  import copy
  import numpy
  import random
  import math
  from .operators import BaseOperator, register_op
  from .batch_operators import Gt2TTFTarget
  from ppdet.modeling.bbox_utils import bbox_iou_np_expand
  from ppdet.utils.logger import setup_logger
  from .op_helper import gaussian_radius
label_desc: Use image node_id 4 for calling the Gt2JDETargetThres obj's underlying member method code with example usage: obj.pad_box(sample, num_max) and returns: sample