Even that trivial `print` annotation breaks duck-typing; the print function can actually accept anything that responds to `__str__`.

Similarly, is there any reason the example `add` function in the OP shouldn't be able to add strings, or lists?

I've seen a lot of these quick-runtime-type-checking libraries, but they always have the same problem as manual type-checking: they make the constraints much stricter than they need to be and prevent entire classes of useful behavior.