class_docstr: Base class of audio classification dataset.
class_docstr_tok: ["Base","class","of","audio","classification","dataset","."]
code: def __len__(self):
      return len(self.records)
  
imports: import csv
  import io
  import os
  from typing import Dict, List, Optional, Tuple, Union
  import numpy
  import paddle
  from paddlehub.utils.utils import extract_melspectrogram
label_desc: Use image node_id 5 for calling the AudioClassificationDataset obj's underlying member method code with example usage: obj.__len__() and returns: len