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

[Chermside, Michael]

Janto writes:
> Geoff> What about ifelse(condition, then clause[, else clause])? 
> 
> I find it difficult to imagine a situation where the short-circuit
> behavior actually matters. Theoretically an ifelse function doesn't do
> the same thing, but practically it does: Whenever I've used ternary
> ops there weren't any side effects to evaluating both arguments.
> Neither any performance ones.
> 
> Can someone give me a real world example of its usefulness?

Simple example:

    print ifelse(y==0, x/y, "undefined")

In fact, it is QUITE COMMON to use a conditional expression as a
"guard"... checking for a special case in which the general formula
would break. Another example would be:

    y = ifelse( x is None, None, func(x) )

Either of these would, of course, not work without short-circuiting /
lazy evaluation.

-- Michael Chermside