code: def __len__(self):
      return len(self.data)
  
imports: import copy
  import math
  import os
  import torch
  import torch.nn
  import torch.nn.functional
  from torch.utils.data import Dataset, DataLoader
label_desc: Use image node_id 2 for calling the ListDataset obj's underlying member method code with example usage: obj.__len__() and returns: len