Or Cython, which has used a non-standard typing system for years, and is currently working on adopting the new types. 

It’s a very tricky business though, because Cython is generating C code, so it can’t use even semi-dynamic types. E.g. needs to know if something is an actual list, rather than a MutableSequence. 

I wonder how MyPyC handles that. Honestly, I’m concerned that the Trent towards static typing will turn Python into a very different language, as it’s much easy to use “locked down” static types than truly dynamic ones. E.g list rather than MutableSequence, or even better, the Protocol types. 

-CHB