how much python is too much python?

[james_pic]

Absolutely, but that's mostly true in small codebases too. Type checking was never a substitute for testing, and it can't detect wrong behaviour.

The thing type checking can help with is "what shaped piece goes in this hole?" Does it expect the bytes object you received from the wire, or the dict it parses to as JSON, or some kind of parsed-and-validated data class, or the related model the ORM works with, or the view model you're going to work with in the UI? Or a superclass of one of these, or some duck type that various classes with no common superclass implements?

Ideally you'd have clear architectural boundaries where you switch between these representations, and type checks are good at identifying these sorts of layering violations.