code: def __len__(self):
      return self.len
  
file_path: MONAI/tests/test_zipdataset.py
imports: from __future__ import annotations
  import unittest
  import torch
  from parameterized import parameterized
  from monai.data import ZipDataset
label_desc: Use image node_id 2 for calling the Dataset_ obj's underlying member method code with example usage: obj.__len__() and returns: self