class Foo(object):
        def __init__(self):
                self.__call__ = self.__realcall__
        def __realcall__(self):
                return 'foo'

class Bar(object):
        def __init__(self):
                self.__call__ = self.__realcall__
        def __realcall__(self):
                return 'bar'
        def __call__(self):
                return self.__call__()

try:
        print 'Foo:'
        print Foo()()
except:
        import traceback
        traceback.print_exc()

print 'Bar:', Bar()()