code: def __getitem__(self, idx):
      batch0, batch1 = zip(*self.data[idx])
      return tensorize(batch0, self.vocab, assm=False), tensorize(
          batch1, self.vocab, assm=self.y_assm
      )
  
imports: import pickle
  import os
  import random
  import torch
  import numpy
  from torch.utils.data import Dataset, DataLoader
  from .mol_tree import MolTree
  from .jtnn_enc import JTNNEncoder
  from .mpn import MPN
  from .jtmpn import JTMPN
  from .vocab import Vocab
label_desc: Use image node_id 3 for calling the PairTreeDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: tensorize,  tensorize