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

[holger krekel]

Chris Liechti wrote:
> mis6 at pitt.edu (Michele Simionato) wrote in
> news:2259b0e2.0302080516.1c577eb2 at posting.google.com: 
> > "Sean Ross" <frobozz_electric at hotmail.com> wrote in message
> > news:<5DV0a.34649$CF1.1127662 at news20.bellglobal.com>... 
> >> >
> >> >     The proposed syntax is as follows:
> >> >
> >> >         <expression1> if <condition> else <expression2>
> >> >
> >> 
> >> While I do not think this is necessary, I would like to offer an
> >> alternative syntax:
> >> 
> >>     <expression1> when <condition> else <expression2>
> >> 
> > 
> > +1 to "when". To me "if" is associated to the conditional statement, a
> > conditional expression is a conceptually  different thing and needs a
> > different expression. Readability is worth adding a new keyword.
> 
> +1 for 'when', +0 for 'if'
> 
> i'd prefer an other word as the condition and 'then'-part is swapped, 
> compared to other ifs, as statement and in listcomps.
> 
> i think that the ternary operator completes listcomps and i like those.
> also i think it's nice for initialiters:
> 
> class X:
>     def __init__(self, optarg = None):
>         self.someval = optarg when optarg is not None else default_value
> 
> i think an expression is much better here than an if statement in this 
> case.

If i didn't knew the quality of your postings i would think 
your are kidding.  I'd very much prefer

        if optarg is None:
            optarg = default_value

        self.someval = optarg

because this is not only a common idiom (e.g. when you need
default arguments to be lists or dicts) but it also parses
(to me) in an instant.  I doubt that

    self.someval = optarg when optarg is not None else default_value

would ever begin to have the same 'ring' with me.

cheers,

    holger