Python3 in DockerFile running ubuntu::latest

Question

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.

DockerFile:

FROM ubuntu:latest

RUN apt-get update -y && apt-get install -y python-pip python3.5-dev build-essential libpq-dev

....

CMD ["/usr/bin/python", "app.py"]

This runs it in python 2.7. I tried updating to

CMD ["/usr/bin/python3", "parcelnotifer.py"]

but this results in an error

Cannot start service dev: oci runtime error: exec: "/usr/bin/python3": stat /usr/bin/python3: no such file or directory

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

Solution

You can first check where Python is getting installed with which python3 and then put that path into your CMD command.