def froze_it(cls):
    """
    Decorator to prevent from creating attributes in the object ouside __init__().

    This decorator must be applied to the final class (doesn't work if a
    decorated class is inherited).

    Yoann's answer at http://stackoverflow.com/questions/3603502
    """
    cls._frozen = False

    def frozensetattr(self, key, value):
        if self._frozen and not hasattr(self, key):
            raise AttributeError("Attribute '{}' of class '{}' does not exist!"
                  .format(key, cls.__name__))
        else:
            object.__setattr__(self, key, value)

    def init_decorator(func):
        @wraps(func)
        def wrapper(self, *args, **kwargs):
            func(self, *args, **kwargs)
            self._frozen = True
        return wrapper

    cls.__setattr__ = frozensetattr
    cls.__init__ = init_decorator(cls.__init__)

    return cls