code: def __len__(self):
      return self.data.shape[0] // self.seq_len
  
imports: import random
  from pathlib import PurePath, Path
  from typing import List, Callable, Dict, Optional
  import torch
  from torch.utils.data import IterableDataset, Dataset
  from labml import monit
  from labml.utils.download import download_file
label_desc: Use image node_id 2 for calling the SequentialDataLoader obj's underlying member method code with example usage: obj.__len__() and returns: unknown