class_docstr: Fake vectorizer which converts document just to a vector of ones 
code: def _featname(self, idx, token):
      # type: (int, str) -> str
      return "[{}] {}".format(idx, token)
  
file_path: eli5/eli5/lime/_vectorizer.py
imports: from __future__ import absolute_import
  from typing import Tuple, Callable, Dict, Optional, List
  import numpy
  from sklearn.base import BaseEstimator, TransformerMixin
  from eli5.base import DocWeightedSpans, FeatureWeights
  from eli5.sklearn.text import _get_feature_weights_dict
  from .textutils import TokenizedText
label_desc: Use image node_id 5 for calling the SingleDocumentVectorizer obj's underlying member method code with example usage: obj._featname(idx, token) and returns: str