text: #!/usr/bin/env python3
  
  # Copyright (c) Facebook, Inc. and its affiliates.
  # This source code is licensed under the MIT license found in the
  # LICENSE file in the root directory of this source tree.
  #
  # Download and build the data if it does not exist.
  
  import parlai.core.build_data as build_data
  import os
  
  
  def build(opt):
      dpath = os.path.join(opt['datapath'], 'mnist')
      version = None
  
      if not build_data.built(dpath, version_string=version):
          print('[building data: ' + dpath + ']')
          if build_data.built(dpath):
              # An older version exists, so remove these outdated files.
              build_data.remove_dir(dpath)
          build_data.make_dir(dpath)
  
          # Download the data.
          fname = 'mnist.tar.gz'
          url = 'http://parl.ai/downloads/mnist/' + fname
          build_data.download(url, dpath, fname)
          build_data.untar(dpath, fname)
  
          # Mark the data as built.
          build_data.mark_done(dpath, version_string=version)
  