title: Python starmap got multiple values for argument
body: <p>I hava a multiprocess program whcich using <code>starmap</code>. But when I run it, a <code>TypeError</code> occured. While normally when I run it in <code>map</code>.</p>
  <pre class="lang-py prettyprint-override"><code>def process_single_image(img_path, target_dir=&quot;&quot;, func=None, severity=1):
      print(target_dir)
      ...
  </code></pre>
  <pre class="lang-py prettyprint-override"><code>pool.starmap(
      partial(
          process_single_image,
          target_dir=target_dir,
          func=iaa.imgcorruptlike.apply_shot_noise,
          severity=4,
      ),
      img_paths,
  )
  </code></pre>
  <p>I don't know why I got this error. I think it should run normally as <code>pool.map(....)</code>.
  Here is the traceback.
  <a href="https://i.stack.imgur.com/99Lsu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/99Lsu.png" alt="enter image description here" /></a></p>