Does anyone know what the mechanism is to default ...
# developmentw
wide-midnight-78598
11/12/2025, 9:57 PMDoes anyone know what the mechanism is to default to having tests run on a specific Python version?
Pylint's default_interpreter_constraints start at 3.10 - but, I have 3.9 installed on my machine, and for some reason, that keeps getting used to run my tests by default
I don't want to decorate every function, so should I override at the BUILD level?
I have explicitly backported tests to run too, for 3.8/3.9
p
proud-dentist-22844
11/12/2025, 10:01 PMIf tests don't specify their constraints, like I do here:
https://github.com/pantsbuild/pants/pull/22873/files#diff-bb2cf38bcbdadbc043547eff384ecdefda3a8624ba6c6b77032c64a2a191aad4R56-R61
Then, they're subject to the default interpreter_constraints here:
https://github.com/pantsbuild/pants/blob/main/src/python/pants/testutil/python_rule_runner.py#L19-L25
And then pex picks the oldest compatible version within the interpreter-constraints range it receives from the given search paths. (iirc)
proud-dentist-22844
11/12/2025, 10:03 PMAt least, that's how it works for
RuleRunnerPythonRuleRunnerrun_pantspants.tomlproud-dentist-22844
11/12/2025, 10:05 PMAlso, if pex does pick a python that is too old initially, and then finds that it is not compatible with the requested interpreter constraints, it should reexec with an appropriate python version.
w
wide-midnight-78598
11/12/2025, 10:06 PMOkay, so, the most reasonable approach seems to be to default a python version, and then override it as necessary. That’s what I was doing, but it didn’t really feel right - given that I’m sending in the pylint interpreter constraints. Thought that would be enough to ensure we used AT LEAST that one in the rule runner
p
proud-dentist-22844
11/12/2025, 10:09 PMThe tests can also modify the python search paths. For my personal use, I added these alias flags to force using a particular python version, so tests could do something similar:
Copy code
$ cat ~/.pants.rc
[cli.alias]
--py36 = "--python-bootstrap-search-path=[] --python-bootstrap-search-path=/home/cognifloyd/.pyenv/versions/3.6.15/bin/python3.6"
--py37 = "--python-bootstrap-search-path=[] --python-bootstrap-search-path=/home/cognifloyd/.pyenv/versions/3.7.17/bin/python3.7"
--py38 = "--python-bootstrap-search-path=[] --python-bootstrap-search-path=/home/cognifloyd/.pyenv/versions/3.8.18/bin/python3.8"
--py39 = "--python-bootstrap-search-path=[] --python-bootstrap-search-path=/home/cognifloyd/.pyenv/versions/3.9.18/bin/python3.9"
--py310 = "--python-bootstrap-search-path=[] --python-bootstrap-search-path=/usr/bin/python3.10"
--py311 = "--python-bootstrap-search-path=[] --python-bootstrap-search-path=/home/cognifloyd/.pyenv/versions/3.11.8/bin/python3.11"w
wide-midnight-78598
11/12/2025, 10:10 PMYeah, this is for ci too - latest pylint drops 3.9
wide-midnight-78598
11/12/2025, 10:10 PMBut i dont want to change our defaults yet, to avoid too much churn at once
p
proud-dentist-22844
11/12/2025, 10:10 PMoh fun. That's probably wise.
w
wide-midnight-78598
11/12/2025, 10:11 PMEven just the pyupgrade will touch every file, so I’m deferring that too
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