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For review: PEP 308 - If-then-else expression

Paul Moore gustav at morpheus.demon.co.uk
Fri Feb 7 16:05:27 EST 2003 
Andrew Koenig <ark at research.att.com> writes:

> Harvey> What about a built-in function?
>
> Harvey> iff(<condition>, <trueresult>, falseresult) which returns
> Harvey> <trueresult> if <condition> is true, otherwise returns
> Harvey> <falseresult
>
> If it were a function, it would have to evaluate all of its arguments.
> Part of the point is that only one of the two results is evaluated.

Interestingly (maybe), your example from another post

    strs = [("?" if i < 0 else str(i)) for i in ints]

didn't need only one of the results to be evaluated.

I'd be interested to know how many real cases would actually rely on
short-circuit evaluation. And those that don't can quite happily be
handled with

    def iff(cond, trueval, falseval):
        if cond:
            return trueval
        else:
            return falseval

(oh, and this function is short enough, and I expect its use to be
rare enough, that I see no need for it to be builtin).

But I do agree that if anything justifies the need for conditional
expressions, it's use in lambda and list comprehensions.

Personally, I don't see enough of a need to be worth it, though.

Paul.
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