code: def _maybe_download_corpus(tmp_dir):
      """Download and unpack the corpus.
  
      Args:
        tmp_dir: directory containing dataset.
  
      Returns:
        path to entire corpus as a text file.
      """
      corpus_url = "http://mattmahoney.net/dc/enwik8.zip"
      corpus_filename = os.path.basename(corpus_url)
      compressed_filepath = generator_utils.maybe_download(
          tmp_dir, corpus_filename, corpus_url
      )
  
      zip_ref = zipfile.ZipFile(compressed_filepath, "r")
      zip_ref.extractall(tmp_dir)
      zip_ref.close()
  
      return os.path.join(tmp_dir, "enwik8")
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import zipfile
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_problems
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 1 for calling a global function with example usage: _maybe_download_corpus(tmp_dir) and returns: os