I'd also strongly recommend only using this in Creative Mode - at least for the moment. As there's not crouch toggle yet (see below) it's far too easy to fall off ledges and hurt/kill yourself. Run ...

By default, macOS comes with Python 2.7.3 installed. We don’t recommend using this version, though, as it’s now deprecated. A common way to install Python 3 is through the dedicated installer. This ...