class_docstr: vocabulary 
code: def __init__(self, use_default_dict):
      self._padding_token = "<pad>"
      self._unknown_token = "<unk>"
      self._start_of_sentence = "<sos>"
      self._end_of_sentence = "<eos>"
      self._s_token = "<s>"
      self._slash_s_token = "</s>"
      self._default_dict = {
          self._padding_token: 0,
          self._s_token: 1,
          self._slash_s_token: 2,
          self._unknown_token: 3,
          self._start_of_sentence: 4,
          self._end_of_sentence: 5,
      }
      self.use_default_dict = use_default_dict
      if self.use_default_dict:
          self._mapping = copy.deepcopy(self._default_dict)
      else:
          self._mapping = {}
      self._freq = collections.defaultdict(int)
  
file_path: delta/delta/data/utils/vocabulary.py
imports: import copy
  import collections
label_desc: Use image node_id 1 to create a new Vocabulary object  with example: obj = Vocabulary(use_default_dict)