link python to python3 code example

Example 1: update link python is python 3

$ python --version
Python 2.7.6
$ python3 --version
Python 3.4.3
$ alias python=python3
$ python --version
Python 3.4.3

Example 2: link python3 to python3.7

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

Example 3: update link python is python 3

$ \python --version 
Python 2.7.6