code: def __len__(self):
      return self.tri_total
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import random
  import numpy
  import torch
  from torch.utils.data import Dataset, DataLoader
label_desc: Use image node_id 2 for calling the PyTorchTrainDataset obj's underlying member method code with example usage: obj.__len__() and returns: self