Update python script shebang line to python3

[cwhite911]

Updated python script shebang to enforce python3 instead of python.

[wenzeslaus]

We went through these switches several times. What is the current practice? What do the distros want?

[cwhite911]

What I've always thought was use python3 if you want to be explicit about not running python2.

[echoix]

See
https://docs.python.org/3/tutorial/appendix.html#executable-python-scripts

https://docs.astral.sh/ruff/rules/shebang-missing-python/

All the rules of https://docs.astral.sh/ruff/rules/#flake8-executable-exe

[cwhite911]

So it looks like #!/usr/bin/env python3 is the recommended version.

[echoix]

Also, it should only be for files intended to be run as scripts directly. Library code, imported, shouldn't be