Until two years ago, Google App Engine only supported Python 2. Therefore, if you wanted to build an app that ran on this service, you needed to use Python 2 and not Python 3.

Learn how to make a game in Python using the popular Pygame. You'll learn how to handle player inputs, draw graphics, and more. How to make a game in Python: Step by step tutorial - Android Authority ...

That could happen thanks to BeeWare, an open-source project headed up Russell Keith-Magee, which is porting CPython to Android, so apps written in Python can run natively on Android.