code: def __len__(self):
      return len(self.sample_list)
  
imports: import json
  import copy
  import os
  import numpy
  import paddle
  from paddleseg.transforms import Compose
  from paddlepanseg.cvlibs import build_info_dict
label_desc: Use image node_id 4 for calling the PanopticDataset obj's underlying member method code with example usage: obj.__len__() and returns: len