Are you talking about Pythonista? It's a whole IDE with GUI designer that includes a bunch of custom libraries for iOS functionality. It's not just an interpreter, and it's not even the top App Store search result for "Python". It is the best Python app on iOS by a wide margin though, which is how it made one of Apple's "featured" lists on the App Store.

Apple doesn't integrate Pythonista into their apps, as far as I know.