Find the number of CPUs in tox.ini
<p>I know how to find the <a href="https://stackoverflow.com/a/1006301/232794">number of CPUs using Python</a>, but how do I do that within a tox.ini file?</p>

<p>What I want is something akin to this:</p>

<pre><code>commands =
  py.test --cov=ook -n ${number_of_cpu_I_can_use}
</code></pre>