class_docstr: Stream-51 Pytorch Dataset
code: def _download_dataset(self) -> None:
      self._download_file(
          stream51_data.name[1],
          stream51_data.name[0],
          stream51_data.name[2],
      )
  
      if self.verbose:
          print("[Stream-51] Extracting dataset...")
  
      if stream51_data.name[1].endswith(".zip"):
          lfilename = self.root / stream51_data.name[0]
          with ZipFile(str(lfilename), "r") as zipf:
              for member in zipf.namelist():
                  filename = os.path.basename(member)
                  # skip directories
                  if not filename:
                      continue
  
                  # copy file (taken from zipfile's extract)
                  source = zipf.open(member)
                  if "json" in filename:
                      target = open(str(self.root / filename), "wb")
                  else:
                      dest_folder = os.path.join(
                          *(member.split(os.path.sep)[1:-1])
                      )
                      dest_folder_path = self.root / dest_folder
                      dest_folder_path.mkdir(
                          exist_ok=True, parents=True
                      )
  
                      target = open(
                          str(dest_folder_path / filename), "wb"
                      )
                  with source, target:
                      shutil.copyfileobj(source, target)
  
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 2 for calling the Stream51 obj's underlying member method code with example usage: obj._download_dataset() without return types