Python 3.9

[LinnaViljami]

I would need python3.9 support in my project. Currently there is no docker-image with python3.9 support

[CamJN]

Python 3.8.2 is the latest provided by Ubuntu 20.04 Focal, it would be appreciated if a PR could be made to improve the python support in this project.

[mathieujobin]

looks like you need to add a ppa and you can install it, a few lines in your Dockerfile and you should be good

ref: https://linuxize.com/post/how-to-install-python-3-9-on-ubuntu-20-04/

[ajhodgson]

#376 (not yet released) updated the provided python installation script to be able to install any supported version of Python from base or the Deadsnakes PPA, using the phusion/passenger-customizable image.

RUN /pd_build/python.sh 3.9