There was an article the other day about problems mixing different python versions on Mac. I admittedly didn't read much of it—but I was somewhat baffled by the problem. I have Python 3 installed on my mac as "python3", and Python 2 (which comes with macOS) as just "python". I think that's the right way to treat them—as different, independent interpreters which can co-exist, as do, say, Python and Ruby.