RegEx Notepad++ Python Script to change Date Format

Gang...I need a notepad++ python script teaching moment.

I want to find and replace a date format (MM/DD/YY and replace with YYYY-MM-DD) another. In NotePad++ RegEx I can do this with

Find: (([0-9]+)/+([0-9]+)/+([0-9]+))

Replace: 20\3-\1-\2

Would someone show me a notepad++ python script that will accomplish the same thing? I think my knowledge gap is in group replacement