class_docstr: A base class for common vocabulary operations. Each subclass should at least 
  implement its own build_vocab() function.
code: def __init__(self, data=None, lang="", idx=0, cutoff=0, lower=False):
      self.data = data
      self.lang = lang
      self.idx = idx
      self.cutoff = cutoff
      self.lower = lower
      if data is not None:
          self.build_vocab()
      self.state_attrs = [
          "lang",
          "idx",
          "cutoff",
          "lower",
          "_unit2id",
          "_id2unit",
      ]
  
imports: from copy import copy
  from collections import Counter, OrderedDict
  from collections.abc import Iterable
  import os
  import pickle
label_desc: Use image node_id 1 to create a new BaseVocab object  with example: obj = BaseVocab(data, lang, idx, cutoff, lower)