#18662 Wrong version of Python used to build `pex_binary` targets in `2.16.0rc0` Issue created by danxmoran Describe the bug • Our CI image contains both Python 3.8 and 3.9. • We set

[python].interpreter_constraints = ["==3.8.*"]

in

pants.toml

. • At least one

pex_binary

depends on a version of

numpy

that (for reasons we haven't dug into) only works with Python 3.8, not Python 3.9 • We haven't investigated the build failures because we expect everything to run against Python 3.8 as configured by

[python].interpreter_constraints

After upgrading to Pants 2.16.0rc0 we see failures building the

pex_binary

in CI, with errors that indicate the build process is trying to build a dependency (

numpy

) against Python 3.9 instead of the expected/configured Python 3.8 This is very concerning. We still run Python 3.8 everywhere in production, so I don't want Pexes to be building against Python 3.9. I've downgraded us back to 2.16.0a1 for now and confirmed this fixes the problem. Pants version 2.16.0rc0 OS Linux Additional info I am suspicious of d3d3257 and e8d387b pantsbuild/pants