pytype (Google) [1], PyAnnotate (Dropbox) [2], and MonkeyType (Instagram) [3] all do dynamic / runtime PEP-484 type annotation type inference [4]

[1] https://github.com/google/pytype

[2] https://github.com/dropbox/pyannotate

[3] https://github.com/Instagram/MonkeyType

[4] https://news.ycombinator.com/item?id=19454411