formula is now named just 'python'. For the homebrew version installed on Travis (which we don't autoupdate) we *should* get python3.6 with this currently. It might be the case that python3 is already installed on Travis macOS image, but need to check. We call tox with 'TOXENV=py3' so that when Travis updates its homebrew, we'll get python3.7 automatically. Finally, use virtualenv instead of venv on mac to fix tox bootstrapping issue https://github.com/pypa/virtualenv/issues/1051 https://github.com/pre-commit/pre-commit/issues/631 https://travis-ci.org/fonttools/fonttools/jobs/427582922#L214 fixup