title: Unable to create custom image for dataproc
body: <p>I am trying to create custom image for my dataproc cluster as per this document <a href="https://cloud.google.com/dataproc/docs/guides/dataproc-images" rel="nofollow noreferrer">https://cloud.google.com/dataproc/docs/guides/dataproc-images</a>. However, it is throwing this error. could you please help ?</p>
  
  <blockquote>
    <p>Traceback (most recent call last):   File "generate_custom_image.py",
    line 419, in 
        run()   File "generate_custom_image.py", line 360, in run
        dataproc_base_image = get_dataproc_base_image(args.dataproc_version)   File
    "generate_custom_image.py", line 98, in get_dataproc_base_image
        if stdout and isinstance(stdout, basestring): NameError: name 'basestring' is not defined</p>
  </blockquote>