code: def maybe_download_file(url, datadir=None, force=False):
      try:
          from urllib.request import urlretrieve
      except ImportError:
          from urllib import urlretrieve
  
      if not datadir:
          datadir = tempfile.gettempdir()
      file_name = url[url.rfind("/") + 1 :]
      dest_file = os.path.join(datadir, file_name)
  
      isfile = os.path.isfile(dest_file)
  
      if force or not isfile:
          urlretrieve(url, dest_file)
      return dest_file
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  import array
  import functools
  import gzip
  import operator
  import os
  import struct
  import tempfile
  import sys
  import warnings
  import numpy
  import tensorflow
  from cleverhans import utils
label_desc: Use image node_id 1 for calling a global function with example usage: maybe_download_file(url, datadir, force) and returns: dest_file