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

[Paul Rubin]

"Paul Paterson" <hamonlypaulpaterson at houston.rr.com> writes:
> However, for me this is the crux of the matter. Short circuiting pretty much
> has to be the justification for implementing this PEP because if you don't
> need short-circuiting you can write a trivial three line iff function. But
> then if short-circuiting is the main reason then I think I'd rather open up
> the general idea of how to implement lazy evaulation in a Pythonic way.

How about further abuse of colon:

   f(:expression)

is short for f(lambda: expression)

So we'd implement a conditional expression with

   def cond(condition, v1, v2):
      if condition:
         return v1()
      else:
        return v2()

To call it, we'd say, for example,

   print cond(x >= 0, :sqrt(x), :"imaginary roots")


I don't see immediately whether this makes any syntax ambiguities with
existing statements, since I can't think of anyplace where colon can
currently appear where an expression can also appear.