This type of hinting would only break type ducking in-so-much as a function that leveraged that hinting would be looking specifically for an instance of a particular type, which would be absolutely no different than a developer performing the type check manually and throwing it out if the type were invalid. It would otherwise just be a lot of tedious and repetitive work for the developer.
The fact is, as valuable as type ducking is, it has drawbacks in its ambiguousness, that are especially harmful to large systems that are being developed with many hands in the pot. And no, people who use a library that leverages this type of hinting are most certainly no more effected by it than they would be by the methods performing the check manually. As the feature is optional, if you want to allow a method that allows for type ducking, you would write it in exactly the same way you write it now, and nobody would be harmed in the process. -- http://mail.python.org/mailman/listinfo/python-list
