Solution for InterpreterNotFound errors from tox

[samredai]

It's expected that developers won't conveniently have python 3.7, 3.8 and 3.9 installed for tox to use for tests so I've added a recommendation to use pyenv to the python README. This is what I do locally and it works nicely. The content here is definitely more for the CONTRIBUTING.md file but I think it's ok here in the readme during the refactoring.

If anyone else feels there's a better local setup to recommend, let me know!

[samredai]

cc: @cabhishek @CircArgs @dramaticlly @rdblue

[cabhishek]

Thanks for the PR. Wondering if versioning needs to be strict up to patch level? or just 3.8.* should suffice?

[kbendick]

I do think it would be ok to do without the strict patch level.

That said, since we do test against these specific patch versions, I also don't see a problem with setting it. We'll probably want to keep this up to date though.

[samredai]

Agreed. It would definitely be safe to just install the latest patch version but unfortunately pyenv doesn't allow excluding it such as 3.8 or 3.8.*. They explain some of the rationale in this issue.

One bug (I think?) in pyenv is that if you have multiple versions inside the python-version file, it doesn't know how to pick them all up when you run the shorthand pyenv install command. It's interesting though because pyenv creates that file on its own.

To be clear about what I mean, if you run pyenv local 3.9.10 it will create a .python-version file that looks like this:

3.9.10

and then someone else can come along and just run pyenv install in that directory and it will install 3.9.10.

However, if you do pyenv local 3.7.12 3.8.12 3.9.10, it creates a .python-version file that looks like ours:

3.7.12
3.8.12
3.9.10

but running pyenv install doesn't work:

$ pyenv install
python-build: definition not found: 3.7.12
3.8.12
3.9.10

The following versions contain `3.7.12
3.8.12
3.9.10' in the name:
  3.7.12
  3.8.12
  3.9.10

See all available versions with `pyenv install --list'.

If the version you need is missing, try upgrading pyenv:

  brew update && brew upgrade pyenv

If it's a simple fix in pyenv-install to get it to iterate and install each version, then it might be worth trying a PR there.

[dramaticlly]

Thank you Sam, I did try your suggestion and it helps!

earlier I was saying my pyenv cannot find the 3.9.10 but after brew update pyenv it works

[dramaticlly]

looks great, I am thinking maybe move tox after pyenv setup will be a good way to validate :)

[rdblue]

Thanks @samredai!