MacOS – Hazel rule using Python script

The approach given here looks a little simpler—maybe it would work for you?

If you don't want to remember to type "quit" instead of "exit", and you're using bash, just add the following to your .bashrc or other shell startup script:

trap '/usr/bin/osascript -e "tell application \"terminal\" to quit"' 0

What's it do? When the shell receives signal 0 (zero), that is, told to exit, it will execute this command as the last thing it does. This allows your shell, etc, to exit gracefully, and asking Terminal.app to exit via applescript makes sure it does the same. In other words, type 'exit', and your shell exits, then Terminal quits, all cleanly and the way nature intended.

The full thread can be found here.

At least with MacPorts, this is done with the python_select command. It may not be immediately applicable to your setup (you didn't mention MacPorts) but it's somewhere to start.