code: def wiki(wiki_root, wiki_date, wiki_language, max_vocab_size=None):
      
      data = WikiDumpStream(
          root=os.path.expanduser(wiki_root), language=wiki_language,
          date=wiki_date)
      vocab = data.vocab
      if max_vocab_size:
          for token in vocab.idx_to_token[max_vocab_size:]:
              vocab.token_to_idx.pop(token)
          vocab.idx_to_token = vocab.idx_to_token[:max_vocab_size]
      idx_to_counts = data.idx_to_counts
  
      def code(shard):
          return [[vocab[token] for token in sentence if token in vocab]
                  for sentence in shard]
  
      data = data.transform(code)
      return data, vocab, idx_to_counts
docs: Wikipedia dump helper.
  
      Parameters
      ----------
      wiki_root : str
          Parameter for WikiDumpStream
      wiki_date : str
          Parameter for WikiDumpStream
      wiki_language : str
          Parameter for WikiDumpStream
      max_vocab_size : int, optional
          Specifies a maximum size for the vocabulary.
  
      Returns
      -------
      gluonnlp.data.DataStream
          Each sample is a valid input to
          gluonnlp.data.EmbeddingCenterContextBatchify.
      gluonnlp.Vocab
          Vocabulary of all tokens in the Wikipedia corpus as provided by
          WikiDumpStream but with maximum size max_vocab_size.
      idx_to_counts : list of int
          Mapping from token indices to their occurrence-counts in the Wikipedia
          corpus.