title: Python3 in DockerFile running ubuntu::latest
body: <p>I am trying to upgrade from running my script in Python 2.7 to Python 3.5. It is a simple Flask admin script running inside a docker container.</p>
  
  <p>DockerFile:</p>
  
  <pre><code>FROM ubuntu:latest
  
  RUN apt-get update -y &amp;&amp; apt-get install -y python-pip python3.5-dev build-essential libpq-dev
  
  ....
  
  CMD ["/usr/bin/python", "app.py"]
  </code></pre>
  
  <p>This runs it in python 2.7. I tried updating to </p>
  
  <pre><code>CMD ["/usr/bin/python3", "parcelnotifer.py"]
  </code></pre>
  
  <p>but this results in an error</p>
  
  <blockquote>
    <p>Cannot start service dev: oci runtime error: exec: "/usr/bin/python3": stat /usr/bin/python3: no such file or directory</p>
  </blockquote>
  
  <p>If I docker exec into the container when it is running on 2.7 I can use the command python3 so Python3 is definitely installed I am just not sure how to force the script to run in Python3</p>