code: def download_file(fname, target_dir=None, force=False):
      
      target_dir = target_dir or temporary_dir()
      target_fname = os.path.join(target_dir, fname)
  
      if force or not os.path.isfile(target_fname):
          url = urljoin(datasets_url, fname)
          urlretrieve(url, target_fname)
  
      return target_fname
docs: Download fname from the datasets_url, and save it to target_dir,
      unless the file already exists, and force is False.
  
      Parameters
      ----------
      fname : str
          Name of the file to download
  
      target_dir : str
          Directory where to store the file
  
      force : bool
          Force downloading the file, if it already exists
  
      Returns
      -------
      fname : str
          Full path of the downloaded file