[ZPT] If/else?

[Brent M Hendricks]

On Wed, May 09, 2001 at 06:15:15PM -0500, Guido van Rossum wrote:
> Evan's latest hacks for this added "(if)" and "(if exists)" to the
> path syntax.  Our latest proposal will remove these again, and add a
> simpler mechanism instead: "x | y | z" will evaluate to the path x if
> it is defined and non-empty, otherwise to y if it is defined and
> non-empty, otherwise to z (which must be defined, but may be empty).

Very nice!  There's a certain elegance to it.

> For those cases where the |-separated sequence doesn't have enough
> expressive power, we propose to fall back on Python expressions
> ("python:<expression>") which are all-powerful, or Python scripts.  In
> order to make testing of paths in Python expressions more convenient,
> we propose adding some simple functions to Python (in the context of
> TALES Python expressions and Zope Python scripts) like
> cond(<expr>, <expr>, <expr>) which serves as a simple if-then-else,

I'm a little unclear on cond().  For example, take 
cond<expA, expB, expC).  Does it transmlate into

if (expA):
   expB
else:
  expC

Or is it more akin to the "x|y|z" construct for path expressions,
returning the first one that is defined and non-empty?


--Brent

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