code: def _get_idx(self, item):
      if item in self.vocab.stoi:
          return self.vocab.stoi[item]
      else:
          return self.vocab.stoi[self.unkify_func(item)]
  
file_path: pytext/pytext/fields/text_field_with_special_unk.py
imports: from collections import Counter, OrderedDict
  from itertools import chain
  from typing import List, Optional, Tuple, Union
  import six
  import torch
  from pytext.common.constants import VocabMeta
  from pytext.fields import TextFeatureField
  from pytext.legacy import data
  from pytext.utils.data import is_number, unkify
label_desc: Use image node_id 4 for calling the TextFeatureFieldWithSpecialUnk obj's underlying member method code with example usage: obj._get_idx(item) and returns: self, self