"?:", "a and b or c" or "iif"

[Michael Hudson]

Thomas Wouters <thomas at xs4all.nl> writes:
> On Tue, May 25, 1999 at 04:35:19PM +0000, Fred L. Drake wrote:
> 
> >   Assuming you're emulating "x ? a : b"....
> >   This isn't quite it.  Using C's ?:, only one of a or b is evaluated
> > when the expression is evaluated.  iif(x, a, b) evaluates both a and
> > b.  Sometimes this is acceptable, but not if either a or b has side
> > effects or is expensive to evaluate.
> 
> [..]
> 
> >   Perhaps Python 2 can fix this shortcoming; I'd often like to use
> > something equivalent to ?:.
> 
> Wait, wait. What's wrong with using 
> 
> x and a or b
> 
> for constructs similar to '?:' ? It shortcuts like '?:', and you can nest it
> to create those hideously unreadable lines C programmers love so much :) (To
> be honest, i love them too, in C, when i dont care about readability. I even
> used to use them in MOO a lot -- i have two lines of 300+ characters with 7
> layers of '?|' (MOO's '?:') constructs, on some old MOO object.)
> 
> Earlier someone said it wasn't equivalent -- but why not ? 

If a is a false value in "x and a or b", then the expression *always*
resolves to b. That's why not.

> At least it's
> more equivalent than an iif() function, isn't it ? Excuse my ignorance if i
> missed something obvious.

No, it's not obvious - and that's the problem.

1-and-0-or-1-ly y'rs Michael