class_docstr: *GTZAN* :cite:`tzanetakis_essl_cook_2001` dataset.
  
  Note:
      Please see http://marsyas.info/downloads/datasets.html if you are planning to use
      this dataset to publish results.
  
  Note:
      As of October 2022, the download link is not currently working. Setting ``download=True``
      in GTZAN dataset will result in a URL connection error.
  
  Args:
      root (str or Path): Path to the directory where the dataset is found or downloaded.
      url (str, optional): The URL to download the dataset from.
          (default: ``"http://opihi.cs.uvic.ca/sound/genres.tar.gz"``)
      folder_in_archive (str, optional): The top-level directory of the dataset.
      download (bool, optional):
          Whether to download the dataset if it is not found at root path. (default: ``False``).
      subset (str or None, optional): Which subset of the dataset to use.
          One of ``"training"``, ``"validation"``, ``"testing"`` or ``None``.
          If ``None``, the entire dataset is used. (default: ``None``).
code: def __len__(self) -> int:
      return len(self._walker)
  
file_path: audio/src/torchaudio/datasets/gtzan.py
imports: import os
  from pathlib import Path
  from typing import Optional, Tuple, Union
  import torchaudio
  from torch import Tensor
  from torch.utils.data import Dataset
  from torchaudio._internal import download_url_to_file
  from torchaudio.datasets.utils import _extract_tar
label_desc: Use image node_id 3 for calling the GTZAN obj's underlying member method code with example usage: obj.__len__() and returns: len