I haven't yet -- type annotations in Python 3 still don't seem to have stabilized. Although I admit I haven't looked too deeply into it, I know a bunch of new

I haven't yet -- type annotations in Python 3 still don't seem to have stabilized. Although I admit I haven't looked too deeply into it, I know a bunch of new stuff landed in 3.6. The appeal of a library that adds a functional layer on top of Python is that it partitions "new stuff" from "old stuff". It seems easier to tear out and reimplement if we screw it up, versus type annotations diffusing out into the rest of our codebase.