class_docstr: Stream-51 Pytorch Dataset
code: def __len__(self):
      return len(self.samples)
  
imports: import os
  import shutil
  import json
  import random
  from pathlib import Path
  from typing import Any, List, Optional, Sequence, Tuple, TypeVar, Union
  from torchvision.datasets.folder import default_loader
  from zipfile import ZipFile
  from torchvision.transforms import ToTensor
  from avalanche.benchmarks.datasets import DownloadableDataset, default_dataset_location
  from avalanche.benchmarks.datasets.stream51 import stream51_data
label_desc: Use image node_id 9 for calling the Stream51 obj's underlying member method code with example usage: obj.__len__() and returns: len