On Tue, 19 Apr 2011 16:26:50 +1000, Chris Angelico wrote:
> On Tue, Apr 19, 2011 at 4:23 PM, Kushal Kumaran
> <kushal.kumaran+pyt...@gmail.com> wrote:
>>> if a + b + c + d != 1:
>>> raise ValueError("Exactly one of a, b, c or d must be true.")
>>>
>>>
>> Unless you're sure all of a, b, c, and d are boolean values, an int
>> with a negative value slipping in could result in the sum equaling 1,
>> but more than one of the variables evaluating to True in boolean
>> contexts.
>
> If they're all expressions, then you can easily guarantee that.
*raises eyebrow*
Either of these should do the job:
sum(map(bool, (a, b, c, d)))
sum(bool(x) for x in (a, b, c, d))
but I don't see how
(arbitrary expression) + (another expression) + ... + (last expression)
can have any guarantees applied. I mean, you can't even guarantee that
they won't raise an exception. Can you explain what you mean?
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
