I led a team that wrote an app app engine using python 2. When Google upgraded to python 3 they completely rewrote entire libraries, like the one for datastore,

I led a team that wrote an app app engine using python 2. When Google upgraded to python 3 they completely rewrote entire libraries, like the one for datastore, so we were forced to either rewrite most of our app or to stay on a deprecated platform that stopped getting new updates.