docs: def invert_hashing_and_fit(
          vec,  # type: Union[FeatureUnion, HashingVectorizer]
          docs
      ):
      # type: (...) -> Union[FeatureUnion, InvertableHashingVectorizer]
      """ Create an :class:`~.InvertableHashingVectorizer` from hashing
      vectorizer vec and fit it on docs. If vec is a FeatureUnion, do it for all
      hashing vectorizers in the union.
      Return an :class:`~.InvertableHashingVectorizer`, or a FeatureUnion,
      or an unchanged vectorizer.
      """
      if isinstance(vec, HashingVectorizer):
          vec = InvertableHashingVectorizer(vec)
          vec.fit(docs)
      elif (isinstance(vec, FeatureUnion) and
                any(isinstance(v, HashingVectorizer)
                    for _, v in vec.transformer_list)):
          vec = _fit_invhashing_union(vec, docs)
      return vec