USE_PY39=true

only works with

release.sh

. Normally I think you set

PY=python3.9

. I have an

.envrc

I use

export PY=python3.9
export PANTS_PYTHON_INTERPRETER_CONSTRAINTS=[\'==3.9.*\']
export PANTS_BLACK_INTERPRETER_CONSTRAINTS=[\'==3.9.*\']
export PANTS_POETRY_INTERPRETER_CONSTRAINTS=[\'==3.9.*\']