def next(self): return next_or_prev_in_order(self, False, self.__class__.objects)
def next(self, qs=None): return next_or_prev_in_order(self, False, qs or self.__class__.objects)
def prev(self): return next_or_prev_in_order(self, True, self.__class__.objects)
def prev(self, qs=None): return next_or_prev_in_order(self, True, qs or self.__class__.objects)