Need option for not skipping missing interpreters

[wsanchez]

I really like to have skip_missing_interpreters = True in my tox.ini, because I'm often working on machines that don't have every Python interpreter installed.

But it's a really bad idea in a CI scenario, because environments just pass without doing anything.

I'd love to see an option to set that value back to False, but there's only a CLI option for setting it to True… every flag really should have an opposite.

[obestwalter]

Hi @wsanchez, you could make the value dependent on an env var and get what you want this way.

[tox]
skip_missing_interpreters = {env:TOX_SKIP_MISSING_INTERPRETERS:False}

On your devbox have the env var permanently set by adding it to the initialization of the shell or directly on the command line:

$ TOX_SKIP_MISSING_INTERPRETERS=True tox  #posix

$ set TOX_SKIP_MISSING_INTERPRETERS=True & tox  #windows

CI can then be blissfully unaware of that configuration option and developers can adjust it to their needs.

[asottile]

I for one think this is a good idea, patch incoming :)

[obestwalter]

I am -1 on this. Feels like command line argument inflation for something that is easily solvable with what we have.

[obestwalter]

I would rather introduce accepting an argument for --skip-missing-interpreters that behaves exactly like the configuration option. That would be a breaking change, but much cleaner.

[asottile]

Devils advocate: why even have the command line argument if you could do it with environment variables 😆

[asottile]

more seriously: I think we could change --skip-missing-interpreters to take an argument and preserve the existing behaviour if no argument is passed -- if that's a better option :)

import argparse
import distutils.util

no_arg = object()


parser = argparse.ArgumentParser()
parser.add_argument(
    '--foo', default=no_arg, nargs='?', type=distutils.util.strtobool,
)
args = parser.parse_args()

if args.foo is no_arg:
    print('not present: false')
elif args.foo is None:
    print('old behaviour: true')
else:
    print(f'new behaviour {args.foo}')

$ python3.6 test.py
not present: false
$ python3.6 test.py --foo
old behaviour: true
$ python3.6 test.py --foo=True
new behaviour 1
$ python3.6 test.py --foo=False
new behaviour 0
$ python3.6 test.py --foo=garbage
usage: test.py [-h] [--foo [FOO]]
test.py: error: argument --foo: invalid strtobool value: 'garbage'

[obestwalter]

Now we're getting somewhere :)

[The-Compiler]

That will break when there are arguments following:

$ python3.6 t.py --foo test.py
usage: t.py [-h] [--foo [FOO]]
t.py: error: argument --foo: invalid strtobool value: 'test.py'

[obestwalter]

TBH my feeling is anyway to try to simplify tox configuration instead of piling the features on, so I will stay with my -1 on this.

[The-Compiler]

Maybe tox should just have an -o option to override any ini option, like pytest has? With that, you could do tox -o skip_missing_interpreters=false but also e.g. tox -o distdir=foo, and maybe even tox -o '[testenv:py35]basepython=python3.5'.

[obestwalter]

That sounds like a great direction to me.