code: def __len__(self):
      return self._nclasses
  
imports: import logging
  import os
  import sys
  from argparse import Namespace
  from typing import Any, List
  import pandas
  import torch
  from hydra.experimental import compose, initialize_config_module
  from iopath.common.file_io import g_pathmgr
  from vissl.config import AttrDict
  from vissl.data.dataset_catalog import get_data_files
  from vissl.hooks import default_hook_generator
  from vissl.utils.checkpoint import get_checkpoint_folder
  from vissl.utils.distributed_launcher import launch_distributed
  from vissl.utils.env import set_env_vars
  from vissl.utils.hydra_config import convert_to_attrdict, is_hydra_available, print_cfg
  from vissl.utils.io import load_file, save_file
  from vissl.utils.logger import setup_logging, shutdown_logging
label_desc: Use image node_id 2 for calling the Partitioning obj's underlying member method code with example usage: obj.__len__() and returns: self