Contract verification in Python

import zope.interface.verify

class ITest(zope.interface.Interface):
   def foo(arg1): pass
   def bar(): pass   

class Test(object):
   zope.interface.implements(ITest)
   def foo(self): pass

class Test2(object):
   zope.interface.implements(ITest)
   def foo(self, arg1): pass

class Test3(object):
   zope.interface.implements(ITest)
   def foo(self, arg1): pass
   def bar(self): pass

for cls in (Test, Test2, Test3):
   try:
       if zope.interface.verify.verifyClass(ITest, cls):
           print "OK: %s correctly implements %s" % (cls.__name__, ITest.__name__)
   except Exception, err:
       print "Error detected with %s's implementation: %s" % (cls.__name__, err)