Worth pointing out maybe that MyPy is not a language but a type checker that works with regular Python. I've been getting into the habit of using it on everything I do lately and find it extremely useful. You can even do runtime checking on the types with tools like Enforce [1], and the Molten framework that was posted on here last week [2] uses MyPy typing as a core part of the framework.

[1] https://github.com/RussBaz/enforce [2] https://news.ycombinator.com/item?id=18107818