title: Jupyter won't connect to a kernel
body: <p>I'm using django-extensions and I ran <code>shell_plus --kernel</code> and it output:</p>
  
  <p><code>To connect another client to this kernel, use:
      --existing kernel-6690.json
  </code></p>
  
  <p>Then I tried connecting with Jupyter:</p>
  
  <p><code>$  jupyter notebook --existing=kernel-6690.json
  [W 10:44:59.290 NotebookApp] Unrecognized alias: '--existing=kernel-6690.json', it will probably have no effect.
  ...
  </code></p>
  
  <p>Why doesn't Jupyter connect to the kernel?</p>