code: def __getitem__(self, idx):
      raise NotImplementedError
  
imports: import sys
  import os
  import random
  import pgl
  from pgl.utils.logger import log
  from pgl.graph import Graph, MultiGraph
  import numpy
  import pickle
label_desc: Use image node_id 2 for calling the BaseDataset obj's underlying member method code with example usage: obj.__getitem__(idx) without return types