Right now ./mach python spawns a Python 2 interpreter with the mach environment activated. We should also create ./mach python3 to do the same with the Python 3 environment. I've run into a few places where this would be handy already.
For now I plan on simply adding the new command so we don't need to deal with updating consumers of mach python (it's used in taskcluster land a bunch).
Turns out I don't need to depend on this change after all. And we can use python3 mach python if we really need an interpreter with the Python 3 environment.
python3 mach python