class_docstr: ASR Task 
class_docstr_tok: ["ASR","Task"]
docstr: Vocabulary size. 
docstr_tok: ["Vocabulary","size","."]
code: def vocab_size(self):
      """Vocabulary size."""
      return self._vocab_size
  
imports: import numpy
  import delta.compat
  from absl import logging
  from delta import utils
  from delta.data.utils import espnet_utils
  from delta.utils.register import registers
  from delta.data.task.base_speech_task import SpeechTask
label_desc: Use image node_id 4 for calling the AsrSeqTask obj's underlying member method code with example usage: obj.vocab_size() and returns: self