code: def __len__(self):
      return len(self.disk_dataset)
  
file_path: deepchem/deepchem/data/pytorch_datasets.py
imports: import numpy
  import torch
  import torch.distributed
  from deepchem.data.datasets import NumpyDataset, DiskDataset, ImageDataset
  from typing import Optional
label_desc: Use image node_id 2 for calling the _TorchDiskDataset obj's underlying member method code with example usage: obj.__len__() and returns: len