Does every docker container has a a OS? Does every container have an OS?

For example, the base docker python image
has a default OS in it? I couldn't find any info on Google. 

I am in doubt because there are some images made with Python that use the Alpine OS.
Your docker image could be without an OS, that's called distroless image.

https://docs.docker.com/develop/develop-images/baseimages/

https://github.com/GoogleContainerTools/distroless