cascading python executions only if return code is 0

[Roy Smith]

In article <mailman.4567.1387819120.18130.python-list at python.org>,
 Ethan Furman <ethan at stoneleaf.us> wrote:

> Mostly I don't want newbies thinking "Hey!  I can use assertions for all my 
> confidence testing!"

How about this one, that I wrote yesterday;

        assert second >= self.current_second, "time went backwards"

I think that's pretty high up on the "can never happen" list.