How are "additional environments" calculated? (tox list)

[bittner]

I want to better understand how Tox derives the "additional environments" shown by the tox list command.

For a Tox setup on GitHub using GHA I use tox-gh-actions to determine the environment to run on GHA for a single job of a job matrix (e.g. run py38 on a setup running on Python 3.8, etc.). tox-gh-actions prescribes that you must plot out a Python version ⇔ Tox environment mapping in a [gh-actions] section in a Tox configuration file.

It looks like this, for some reason, results in tox list showing the Python versions as "additional environments", e.g.

$ tox list
default environments:
flake8   -> Static code analysis and code style
isort    -> Ensure imports are ordered consistently
pylint   -> Check for errors and code smells
py27     -> Unit tests and test coverage
py35     -> Unit tests and test coverage
py36     -> Unit tests and test coverage
py37     -> Unit tests and test coverage
py38     -> Unit tests and test coverage
py39     -> Unit tests and test coverage
py310    -> Unit tests and test coverage
py311    -> Unit tests and test coverage
pypy2    -> Unit tests and test coverage
pypy3    -> Unit tests and test coverage
bandit   -> PyCQA security linter
package  -> Build package and check metadata (or upload package)
clean    -> Clean up bytecode and build artifacts

additional environments:
black    -> Ensure consistent code style
license  -> Manage license compliance
2.7      -> Unit tests and test coverage
3.5      -> Unit tests and test coverage
3.6      -> Unit tests and test coverage
3.7      -> Unit tests and test coverage
3.8      -> Unit tests and test coverage
3.9      -> Unit tests and test coverage
3.10     -> Unit tests and test coverage
3.11     -> Unit tests and test coverage
pypy-2.7 -> Unit tests and test coverage
pypy-3.8 -> Unit tests and test coverage

The above output comes from a setup having the following Python version ⇔ Tox environment mapping:

[gh-actions]
python =
    2.7: py27
    3.5: py35
    3.6: py36
    3.7: py37
    3.8: py38
    3.9: py39
    3.10: py310
    3.11: py311
    pypy-2.7: pypy2
    pypy-3.8: pypy3

Why does this happen? Is this behavior intended? If yes, how does one get rid of the, certainly not intentionally set up, "additional environments"?

[gaborbernat]

This is because of a bad design decision of that plugin to use : instead of = for assignment. tox uses : for factor definition so these additional factors get picked up as environments. I recommend using the tox-gh plugin instead that doesn't have this flaw.

[jugmac00]

https://github.com/tox-dev/tox-gh

[bittner]

Thanks for the explanation! That helps.

Unfortunately, tox-gh only supports Python 3.7+. 😟

[gaborbernat]

That's the oldest version supported by CPython.