code: def file_exists(
          download_url,
          filename=None,
          decompress=False,
          subdir=None):
      
      filename = build_local_filename(download_url, filename, decompress)
      full_path = build_path(filename, subdir)
      return os.path.exists(full_path)
docs: Return True if a local file corresponding to these arguments
      exists.