title: No module named ipykernel_launcher
body: <p>I'm trying to register a pyenv-virtual env as a <code>jupiter lab</code> kernel on MacOs. I have this working on ubuntu but I'm running into issues on my MacBook.</p>
  
  <p>I followed the instructions <a href="https://ipython.readthedocs.io/en/latest/install/kernel_install.html" rel="noreferrer">here</a> which creates the following kernel spec file.</p>
  
  <pre><code>{
  "argv": [
  "/Users/david/.pyenv/versions/python36-tf2/bin/python",
  "-m",
  "ipykernel_launcher",
  "-f",
  "{connection_file}"
  ],
  "display_name": "Python (3.6.8 TF2.0)",
  "language": "python"
  }
  </code></pre>
  
  <p>I tested by running <code>Users/david/.pyenv/versions/python36-tf2/bin/python -m 
  ipykernel_launcher</code> and it works fine.</p>
  
  <p>But when I run <code>jupiter lab</code> (system python) then try and use the new kernel it aborts with log messages </p>
  
  <blockquote>
    <p>/Users/david/.pyenv/versions/python36-tf20/bin/python: No module named
    ipykernel_launcher</p>
  </blockquote>
  
  <p>Any ideas how to fix, the pyenv definitely can run <code>ipykernel_launcher</code>?</p>