code: def __len__(self):
      return self.__dataset_len
  
imports: import math
  import os
  import re
  from pathlib import Path
  from typing import Any
  import pytest
  import pytorch_lightning
  import torch
  from omegaconf import OmegaConf
  from omegaconf.errors import OmegaConfBaseException
  from pytorch_lightning import Callback
  from pytorch_lightning.loops import _TrainingEpochLoop
  from nemo.constants import NEMO_ENV_VARNAME_VERSION
  from nemo.core.classes import ModelPT
  from nemo.utils.exp_manager import CheckpointMisconfigurationError, LoggerMisconfigurationError, NotFoundError, exp_manager
label_desc: Use image node_id 3 for calling the OnesDataset obj's underlying member method code with example usage: obj.__len__() and returns: self