code: def __len__(self):
      return len(self.audio_files)
  
imports: import math
  import os
  import random
  import torch
  import torch.utils.data
  import numpy
  from librosa.util import normalize
  from scipy.io.wavfile import read
  from librosa.filters import mel
label_desc: Use image node_id 3 for calling the MelDataset obj's underlying member method code with example usage: obj.__len__() and returns: len