Platform-specific CLI configuration for command without duplication

[smackesey]

I am trying to define a tox.ini that defines platform-dependent config for a single CLI argument in a single command. My current solution uses an environment variable:

commands:
  pylint -j {env:PYLINT_JOBS:0} ...

I would like to get rid of the environment variable and infer the correct setting based on platform. If on macOS, -j 1 should be passed, on all other platforms -j 0 should be passed. I know I can achieve this with:

[tox]
envlist = pylint-{macos,other}

[testenv]
commands =
  macos: pylint -j 1 ...
  other: pylint -j 0 ...

I don't like this solution because:

• It duplicates the entire rest of the command
• It requires the tox invocation to explicitly specify the platform, even though this information can be inferred from sys.platform

Is there any solution that avoids both of the above? I'm hoping for something that basically works like this:

[testenv]
commands =
  pylint -j {sys.platform == 'darwin' ? '1' : '0'} ...

[jugmac00]

I like your second approach the most - this is the one I see quite often in a tox configuration.

If you want to avoid the duplication, you can always create a bash or a Python script as a wrapper around your pylint command.

[Czaki]

It is also possible to workaround this using toxfile.py. The toxfile is a local tox plugin. In my example, I need to have the name of the used platform (to avoid collision of report files). So I use the following code:

from __future__ import annotations

import sys
from typing import TYPE_CHECKING

from tox.plugin import impl

if TYPE_CHECKING:
    from tox.config.sets import EnvConfigSet
    from tox.session.state import State

@impl
def tox_add_env_config(env_conf: EnvConfigSet, state: State) -> None:
    env_conf.add_constant(["sys_platform"], "string representing current OS", sys.platform)
    print("tox_add_env_config", env_conf, state)

And then could use sys_platform as the substitution in the commands definition.