Sometimes, though, you may get lucky, and find some tests for the code you want to use!
On a more serious note, I can't even blame library devs as long as they try. Type "hints" often are anything but _just_ hints. Some are expected to be statically checked; some may alter runtime behavior (e.g. the @overload decorator). It's like the anti-pattern of TypeScript's enums laid out here and there, and it's even harder to notice such side-effects in Python.
On a more serious note, I can't even blame library devs as long as they try. Type "hints" often are anything but _just_ hints. Some are expected to be statically checked; some may alter runtime behavior (e.g. the @overload decorator). It's like the anti-pattern of TypeScript's enums laid out here and there, and it's even harder to notice such side-effects in Python.