http://metabates.com/2011/02/07/building-interfaces-and-abst...
http://docs.python.org/2/library/abc.html
Learn some OOP and design patterns before filling your mouth talking about PHP.
Also, Clojure is a dynamic language too and yet it craves for explicit types:
http://www.indiegogo.com/projects/typed-clojure
But this is only for noobs who "want to feel safe", according to you. What a joke. You probably can't even get past an introductory tutorial of this subject.