Damn, Python is used throughout much of Ubuntu for system scripts and software,
and software relies on having Python (and the commands to start Python)
in a certain spot. do back then.

rm /usr/bin/python3 
ln -s /usr/bin/python3.7 /usr/bin/python3 

# create alias in ~/.bash_aliases

alias python3='/usr/bin/python3.7' 
Scripts can then start with something like:

#!/usr/bin/env python3