code: def __len__(self):
      return self.num_obs
  
file_path: ReAgent/reagent/evaluation/cb/run_synthetic_bandit.py
imports: import uuid
  from typing import List, Tuple
  import pytorch_lightning
  import torch
  from pytorch_lightning import seed_everything
  from reagent.evaluation.cb.synthetic_contextual_bandit_data import DynamicBanditAgent, DynamicBanditEnv
label_desc: Use image node_id 3 for calling the BanditDataset obj's underlying member method code with example usage: obj.__len__() and returns: self