I'm very happy to see this happening. "Optional" type checking for python would be a great addition to the language. For large codebases, use of type checking can really help.

I also like the idea of using annotations instead of decorators (or something like that). I'm already using this for python3 [1] in a non intrusive way, by using assert to disable it on production.

[1] https://pypi.python.org/pypi/optypecheck
--
  Carlo Pires