At least for Python, there are a different set of goals for programmer-productivity type hints (such as these) and for static-compilation type hints (such as you would need to provide optimizations).
One particular point is Python subclasses: it makes a lot of sense to say that a Python subclass is a subtype of the parent class, but in reality there are no guarantees about any relationship. This means that a compiler/VM would most likely have a hard time making use of type annotations since it would have to have to support the user passing arbitrary subclasses with completely different behavior.
One particular point is Python subclasses: it makes a lot of sense to say that a Python subclass is a subtype of the parent class, but in reality there are no guarantees about any relationship. This means that a compiler/VM would most likely have a hard time making use of type annotations since it would have to have to support the user passing arbitrary subclasses with completely different behavior.