Interface and duck typing woes

[Roy Smith]

In article <52200699$0$6599$c3e8da3$5496439d at news.astraweb.com>,
 Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:

> These days, it would be relatively simple to implement pre- and post-
> condition checking using decorators, and indeed one of the motivating use-
> cases for function annotations in Python 3 is to allow such things.
> 
> http://www.python.org/dev/peps/pep-3107/
> 
> (Function annotations are perhaps the best Python feature that nobody 
> uses.)

This is awesome.