title: Why can't I install python3.8-dev on Ubuntu 16.04?
body: <p>This comes as a wider issue of Flask/Apache2.4 throwing a hissy fit over which version of python they want to use, but I can't follow any of the guidance I've found to fix it because I need <code>python3.8-dev</code> and it doesn't want to install:</p>
  <pre><code>apt install python3.8-dev`
  ...
  E: Unable to locate package python3.8-dev
  E: Couldn't find any package by glob 'python3.8-dev'
  E: Couldn't find any package by regex 'python3.8-dev'
  </code></pre>
  <p>I have already done:</p>
  <pre><code>add-apt-repository ppa:deadsnakes/ppa
  apt install software-properties-common
  apt update
  apt upgrade
  </code></pre>
  <p>which all succeed however none have so far led to success with installing python3.8-dev.</p>
  <p>The output of <code>lsb_release -a</code> is:</p>
  <pre><code>No LSB modules are available.
  Distributor ID: Ubuntu
  Description:    Ubuntu 16.04.7 LTS
  Release:        16.04
  Codename:       xenial
  </code></pre>
  <p>I feel like I'm going mad, everything worked fine and today it just doesn't.
  I do of course already have python3.8 installed.</p>