code: def __len__(self) -> int:
      return len(self.train_set)
  
imports: from typing import Any, Dict, Tuple
  import pandas
  import torch
  import torch.utils.data
  from torch.utils.data.distributed import DistributedSampler
label_desc: Use image node_id 2 for calling the Bert4RecTrainDataset obj's underlying member method code with example usage: obj.__len__() and returns: len