Some time ago, I wrote a shopping list app as an exercise to learn Android programming. I do not plan to maintain this or enhance it, but the code is now available.
It is just a couple simple list views. One view adds items to the list. All items ever added remain in that view, the inventory. The other view is the actual shopping list. Tapping an item in the inventory moves it to the shopping list; tapping it in the shopping list moves it back to inventory.
A right or left swipe switches between the views, which brings up an annoying factoid: the Android api does not have built-in swipe detection. Creating your own gesture detector is easy; 30 seconds on Google finds as many slightly different implementations as you could care to see. Nevertheless, swiping is a simple, common need. A side-to-side swipe detector and a zoom detector would probably cover almost every application.
This illustrates another reason to like Python:
Fans of Python use the phrase “batteries included” to describe the standard library, which covers everything from asynchronous processing to zip files.