code: def extend_vocab(self, *args, vectors=None, cache=None):
      sources = []
      for arg in args:
          if isinstance(arg, data.Dataset):
              sources += [
                  getattr(arg, name)
                  for name, field in arg.fields.items()
                  if field is self
              ]
          else:
              sources.append(arg)
  
      tokens = set()
      for source in sources:
          for x in source:
              if not self.sequential:
                  tokens.add(x)
              else:
                  tokens.update(x)
  
      if self.vocab.vectors is not None:
          vectors = MatchingField._get_vector_data(vectors, cache)
          self.vocab.extend_vectors(tokens, vectors)
  
imports: import gzip
  import logging
  import os
  import shutil
  import tarfile
  import zipfile
  import nltk
  import six
  import fasttext
  import torch
  from torchtext.legacy import data, vocab
  from torchtext.utils import download_from_url
  from urllib.request import urlretrieve
label_desc: Use image node_id 6 for calling the MatchingField obj's underlying member method code with example usage: obj.extend_vocab() without return types