targeted's comments

This reminds me of a bug that I found in Borland C++ 14 years ago: http://qc.embarcadero.com/wc/qcmain.aspx?d=3478

Sad to know that after all that time compilers still can't get even the core semantics right.

In Python 3 a similar thing looks better with the use of "function annotations": http://code.activestate.com/recipes/572161/

There also are a few modules out there that implement design-by-contract's pre-/post-conditions for class instances, for example http://code.activestate.com/recipes/436834/