Short-circuit Logic

[Chris Angelico]

On Fri, May 31, 2013 at 1:02 AM, Ethan Furman <ethan at stoneleaf.us> wrote:
> On 05/30/2013 05:58 AM, Chris Angelico wrote:
>> If you iterate from 1000 to 173, you get nowhere. This is the expected
>> behaviour; this is what a C-style for loop would be written as, it's
>> what range() does, it's the normal thing. Going from a particular
>> starting point to a particular ending point that's earlier than the
>> start results in no iterations. The alternative would be an infinite
>> number of iterations, which is far far worse.
>
> If the bug is the extra three zeros (maybe it should have been two), then
> silently skipping the loop is the "far, far worse" scenario.  With the
> infinite loop you at least know something went wrong, and you know it pretty
> darn quick (since you are testing, right? ;).

You're assuming you can casually hit Ctrl-C to stop an infinite loop,
meaning that it's trivial. It's not. Not everything lets you do that;
or possibly halting the process will halt far more than you intended.
What if you're editing live code in something that's had uninterrupted
uptime for over a year? Doing nothing is much safer than getting stuck
in an infinite loop. And yes, I have done exactly that, though not in
Python. Don't forget, your start/stop figures mightn't be constants,
so you might not see it in testing. I can't imagine ANY scenario where
you'd actually *want* the infinite loop behaviour, while there are
plenty where you want it to skip the loop, and would otherwise have to
guard it with an if.

ChrisA