Adding Python Support to a Specific Docker Container

I have been using the hoobs docker container for home automation and I am needing to run a plugin within the container that requires a python environment. It appears that this is fairly simple to do when running hoobs on a raspberry Pi etc as you just install python and away you go. However for the life of me I cannot find any documentation for how to add python to an existing container. I using nerdpack but that seems to just install python at a higher level and the runtime isnt available inside the container. I am still a noob with all of this so any ideas at all are appreciated.