The issue is that sometimes a function can take a type that is an optional dependency, so you don't want to import it unless you are type checking. (And some t

The issue is that sometimes a function can take a type that is an optional dependency, so you don't want to import it unless you are type checking. (And some types are defined in the typeshed so only exist to be imported during type checking; eg the type checker lib itself is a dependency in this case)