My understanding of semantic versioning is that:

- (x+1).0 and (x).0 don't necessarily need to be able to run code writen for the other

- 3.(x-1) doesn't need to be able to run code written for 3.(x)

- 3.(x+1) should always run code written for 3.(x)

Hence, you should be able to point "python3" at the latest subversion of 3 that is available, continually upgrade from 3.6 to 3.7 to 3.8, and as long as you have a higher sub version of 3, you shouldn't break any code that is also written for an earlier subversion of 3. That's why it is supposed to be okay to have them all symlinked to "python3". If a package install candidate thinks the currently running "python3" isn't recent enough for the feature set it needs, it can request the dependency manager upgrade "python3" to the latest 3.(x+n) with the understanding of not breaking any other code on the machine.

Unfortunately that isn't true between 3.7 and 3.8. There are lots of cases where upgrading to 3.8 will break packages and that violates semantic versioning.

...irrelevant, I'm afraid.

Python doesn't use semantic versioning, so you can't really expect them to follow it. As GP insinuated, if you just pretend that 3.7 is 37, and 3.8 is 38, you'll pretty much be able to apply semver thinking, though.

Right, so because Python doesn't coooperate, we end up needing containerization, which is what I was trying to explain in GGGGP. Because apt will upgrade 3.7 to 3.8 and unfortunately break anything that was written in 3.7 (and vice versa).

An app needs to be able to say "I'm ok with python3>=3.7" and be fine if it gets 3.8, 3.9, or 3.20, if we want to be able to run it without a container. (And likewise for all its other dependencies besides python)