On a related note, the proliferation of tested Python versions has led many projects to enable the skip_missing_interpreters option in their tox.ini files. Please don't, this is just plain DANGEROUS. I know it's nice that when you've got a bunch of Python versions in your default tox envlist some of which a typical developer may not have installed, they can still run `tox` and not get errors about those. However, it also means that if you run `tox -e py38` and don't have any Python 3.8 interpreter, tox will happily say it did nothing successfully. Yes it's fairly obvious when you see it happen locally. It's far less obvious when you add a Python 3.8 job in the gate but don't make sure that interpreter is actually installed then and get back a +1 from Zuul when tox ran no tests at all. An alternative solution, which some projects like Zuul have switched to, is not listing a bunch of specific pyXY versions in the tox envlist, but just putting "py3" instead. This will cause folks who are running `tox` to get unit tests with whatever their default python3 interpreter is, but also they'll get a clear error if they don't have any python3 interpreter at all. If someone has Python 3.8 installed and it isn't their default python3 but they still want to test with it, they can of course do `tox -e py38` and that will work as expected. This also means you no longer have to update the envlist in tox.ini every time you add or remove support for a specific interpreter version. Besides, tox.ini is not a good place to list what versions of the interpreter your project supports, that's what trove classifiers in the setup.cfg file are for. -- Jeremy Stanley