Yeah that's only Python 3, which most people aren't using yet. Also it's not optional typing -- it's optional annotations. Someone would still have to actually implement the type checking -- not even sure that's been done.

I have wanted to play around with implementing some type checking, but none of my stuff is Python 3 unfortunately.

Check out MyPy: http://www.mypy-lang.org/ It uses the Python 3 annotations syntax for type checking.

MyPy is the only thing that would make me keep coding in python in the long term.

Do you know how mature it is ?

I read that and it gave me 5 seconds of hope. But then

"The only way that annotations take on meaning is when they are interpreted by third-party libraries"

and

"Following from point 2, this PEP makes no attempt to introduce any kind of standard semantics, even for the built-in types. This work will be left to third-party libraries"

means the author really isn't serious about it. If you don't have a standard semantic you've got nothing useful.