Document supported (session) Python versions

[scop]

How would this feature be useful?

I'm unable to find documentation on which old Python version sessions nox intends to support.

#525 (comment) says

And to be clear, this about installing Nox on Python 3.6. Nox will still create and run sessions on old Pythons.

It would be nice to elaborate on exactly which "old Pythons" in the docs :)

Describe the solution you'd like

Find the above info in docs.

Describe alternatives you've considered

No response

Anything else?

I've found that at least 3.3 is doable currently but requires an additional virtualenv<15.2 constraint, ditto 3.4 with virtualenv<20.5.

Not sure if there's anything nox could do to make that Just Work without users having to figure out and specify the constraints.

[theacodes]

Nox, by nature, supports creating virtualenvs for any Python version that the underlying version of virtualenv supports- which is basically all of them.

[scop]

Having something like that stated in docs would be good enough as far as I'm concerned.

I'd personally omit the "which is basically all of them" part though, because don't think all virtualenv package versions are able to create ones for all Python versions. (Could be something in their dep chain that causes it, but no need to dig in that deep.) Or perhaps I misunderstand what exactly that part refers to, in which case I suggest rephrasing it to clarify ;)

[NickleDave]

I just want to 👍 +1 this--I've had the same question a few times. For a while I thought that nox was using whichever Python pipx installed with, and then finally it dawned on me there was a python parameter for Session.

Very possible I just need to learn to read the docs better but seems like I'm not the only one missing what's there.

I wonder if maybe the first mention of this on index.md could be a little more explicit?

E.g., instead of

For each session, Nox will automatically create a virtualenv with the appropriate interpreter, install the specified dependencies, and run the commands in order.

it could say

For each session, Nox will automatically create a virtual environment with the appropriate Python interpreter, using a backend like virtualenv or conda. Then Nox will install the specified dependencies into that environment, and run the commands in order.