i can't run python 3 when testing pants locally because

PythonInterpreter.all(paths)

isn't finding

/usr/bin/python3.6

, even after

rm -rf ~/.cache/pants/python_cache

and a clean-all, and i think this is actually a tricky pex bug, in that it looks like

PythonInterpreter.all(paths)

will filter out older minor versions for each major version, but it does that before knowing about any interpreter constraints, so it finds python 3.7, discards 3.6, and only then do we find (back in pants, which has the interpreter constraints) that there is no interpreter matching

CPython>=3.4,<3.7

(because 3.6 was filtered out previously) -- it seems like

all()

is thoroughly misnamed