There's a great 5m lightning talk from Pycon 2019 explaining the difference between pytype and mypy[0]. It's great that there's different libraries approaching the problem from different angles. Speaking of which, I'm also curious to see how Facebook's Pyre[1] differs from the former two. I'm surprise there's isn't a comprehensive comparison of the 3 libraries yet.
[0] https://www.youtube.com/watch?v=yFcCuinRVnU&t=38m25s
[1] https://github.com/facebook/pyre-check