"py" command for Linux and Mac?

[Dan Stromberg]

Hi folks.

I heard there's a Windows-like "py" command for Linux (and Mac?).

I'm finally getting to porting a particular project's Python 2.7 code to
3.x, and one of the first steps will probably be changing a lot of "python2
script.py" to use #!/usr/bin/env python2 and chmod +x.  Then we can update
the scripts one at a time to use #!/usr/bin/env python3.

However, would this be Linux-and-Mac-only?  I'm not at all sure this code
will ever move to Windows, but in case it does, would a "py" command work
on all 3 if I use #!/usr/bin/env py?

And if so, where can I find that "py" command for Linux and Mac?

I tried searching for it in Google and on Pypi, but unsurprisingly
searching for "py" gives a buzzillion hits on other things.

Thanks!