
When a formula `depends_on :python` *and* `depends_on :python3` the `modify_build_environment` method sets the PYTHONPATH and the Python 3.x requirement then fails because it finds the sitecustomize.py from Python 2.x in the PYTHONPATH.
When a formula `depends_on :python` *and* `depends_on :python3` the `modify_build_environment` method sets the PYTHONPATH and the Python 3.x requirement then fails because it finds the sitecustomize.py from Python 2.x in the PYTHONPATH.