I recently came across an announcement about the the Strongtalk system, which contains the first fully developed strong, static type system for Smalltalk. I wondered whether there might be useful ideas there for those looking into static typing for Python.

http://www.cs.ucsb.edu/projects/strongtalk/pages/index.html

You have to download and install their Windows app and run it in order to get some documentation about the type system. I did, and it's pretty theoretically clean (as you'd expect from a Smalltalk system). It has a pretty conventional way to describe method signatures, including a way to define type variables implicitly, so you can define e.g. a function taking two lists whose return type is a tuple of the item types of the arguments. One thing that I hadn't seen before is the little language they use that allows you to say things like that. --Guido van Rossum (home page: http://www.python.org/~guido/)