On Wed, 12 Oct 2005 02:15:40 -0400, Chris Smith <[EMAIL PROTECTED]> wrote:
>>>>>> "Sebastian" == Sebastian Bassi <[EMAIL PROTECTED]> writes:
>
> Sebastian> On 9/30/05, Reinhold Birkenfeld <[EMAIL PROTECTED]> wrote:
> >> after Guido's pronouncement yesterday, in one of the next
> >> versions of Python there will be a conditional expression with
> >> the following syntax: X if C else Y
>
> Sebastian> I don't understand why there is a new expression, if
> Sebastian> this could be accomplished with:
>
> Sebastian> if C: X else: Y
>
> Sebastian> What is the advantage with the new expression?
>
>One very frequent use case is building a string.
But what you show doesn't require choice of which to _evaluate_,
since you are merely choosing between immutable constants, and there is
no side effect or computation overhead to avoid by not evaluating
the unselected expression. So
"the answer is " + ('no', 'yes')[X==0]
would do as well.
>Instead of:
>
>if X==0:
> filler="yes"
>else:
> filler="no"
>return "the answer is %s" % filler
>
>
>What I really want to do is take four lines of conditional, and put
>them into one, as well as blow off dealing with a 'filler' variable:
>
>return "the answer is " + "yes" if X==0 else "no"
As has been pointed out, though legal there is some doubt as to whether
you meant what you wrote ;-)
>
>
>Or whatever the final release syntax is.
>Conditional expressions are a nice way to shim something in place, on
>an acute basis. Chronic use of them could lead to a full-on plate of
>spaghetti, where you really wanted code.
>They can be impenitrable. Whenever I'm dealing with them in C/C++, I
>always line the ?, the :, and the ; characters vertically, which may
>seem a bit excessive in terms of whitespace, but provides a nice
>hieroglyph over on the right side of the screen, to make things
>obvious.
>Best,
>Chris
Regards,
Bengt Richter
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