If you wanted to build your own Android app to connect to a Python service, over Bluetooth, to control a Raspberry Pi, you just found the resources to do so. I know there are plenty of apps that control a Raspberry Pi. Most of them connect over SSH and some of them using Bluetooth. However, finding a tutorial that teaches you how to build your own is harder. You can probably do some research like I did and write an app but I haven’t managed to get the whole information in the same place.