Documenting Python versioning and stability expectations

[steve.dower]

Great doc! Just wanted to call out a few things I spotted on my first reading (I’m sure there’ll be a second and third).

@encukou

The expectation is that
the transition to Python 4.0, if and when it happens, will be similar to
the transition to a new minor version.

I would just omit this sentence entirely. Once we get through the double-digit version issues of 3.10, there’s no reason to go to 4 just as a minor version, so I’d expect to see “why bother” arguments at that stage. Preemptively setting expectations is just asking to be proven wrong, and that will confuse (and hence, upset) people who had read it.

@encukou

Despite similarities, Python does not use the popular semantic versioning _
scheme, which was published several decades after Python.

I’d put this much higher up and as prominently as possible. Maybe make it one line with a “Semantic Versioning (SemVer)” heading

@encukou

Security releases are source-only : Windows and macOS installers for
them are not available from python.org _, which means that users of these
binaries …

“… may need to upgrade to the next minor version after the bugfix period ends”

@encukou

Features enabled by :ref: future statements <future> .

Is this referring to the fact that we may add new features (gated behind future imports), or that anything behind a future import may change at any time? Seems like it should only be the former.