A minimal hello world with Python 3 required 7MB. But it's not optimized.
Unlike pyinstaller, we don't scan import to try reducing the distribution on the phone. Instead we have a blacklist.txt which you can put file pattern to exclude during packaging.
I remember for one app in Python 2 to reduce the size around the 5MB.
We won't be able to reduce much more, as Python interpreter is embedded. We also don't want to adopt an approach like Qt where Qt binaries can be shared for all Qt-application, which break the all-in-one APK, open some potential issues, and add more work to manage dependencies.
It looks like a 'Hello World' will result in about a 10 Mib APK which takes up roughly double that space when unpacked on the mobile device. This is not surprising because the APK must contain the Kivy library and a Python interpreter. After that initial hurdle it will scale relatively well, though that can depend on which extensions and other files you include.
If you want a smaller target, VOC (http://pybee.org/voc) can generate a "Hello World" APK in about 1.6MB.
VOC is compiler that takes Python code, and output Java bytecode. This means you can use the Android native UI components, because your Python code becomes indistinguishable from code written in Java. Combine with Briefcase (http://pybee.org/briefcase), and you can get an Android app with one command; combine with Toga (http://pybee.org/toga), and you can get a cross platform app using native system components.
I'm assuming that 10MB would be less if you didn't want to use Kivy. However, I assume that using Django would probably take even more space that Kivy. So could it get big fast?
Python for Android is an extension for Kivy, so it is not optional. It looks like apps could get quite big since adding functionality involves including Python libraries to be called from Python rather than interacting with the Android API.
Kivy actually is completely optional, python-for-android doesn't require any particular frontend. The main supported options for guis other than Kivy are SDL2 (you can use e.g. PySDL2) or a webview, but it's designed to be easy to add more options.
