With Flow in JS, how would a JSON library for similar purposes work where you don't know what kind of data it will be and you will be doing a lot of transformations on it?
One way Mypy could help do this is by implementing a feature like Type Providers https://docs.microsoft.com/en-us/dotnet/fsharp/tutorials/typ...
Scala is a language that is often used for data processing, and is statically typed.
Depending on the situation, codegen can also be useful in these situations, eg; https://github.com/typeorm/typeorm
EDIT: in any case, this certainly answers my question :-) sounds like they're not there yet, and perhaps not even moving in that direction yet.