class_docstr: Sort samples by target length and batch to max token count.
class_docstr_tok: ["Sort","samples","by","target","length","and","batch","to","max","token","count","."]
code: def __len__(self):
      return len(self.batches)
  
imports: from functools import partial
  from typing import List
  import sentencepiece
  import torch
  import torchaudio
  from common import Batch, batch_by_token_count, FunctionalModule, GlobalStatsNormalization, piecewise_linear_log, post_process_hypos, spectrogram_transform, WarmupLR
  from pytorch_lightning import LightningModule
  from torchaudio.models import emformer_rnnt_base, RNNTBeamSearch
  from .dataset import MUSTC
label_desc: Use image node_id 3 for calling the CustomDataset obj's underlying member method code with example usage: obj.__len__() and returns: len