[Python-Dev] Adding a conditional expression in Py3.0

[Jason Orendorff]

On 9/20/05, Guido wrote:
> On 9/20/05, Jason Orendorff <jason.orendorff at gmail.com> wrote:
> >     return (if q: q.popleft() else: None)
> >     return (if q then q.popleft() else None)
> >     return q ? q.popleft() : None
> >
> > Hmmm.  Score one for ?:.
>
> Why? Just because it's shorter?

Just a gut response to the look.  The verbose forms strike me as
cluttered in this particular case.

In the multiline case, it doesn't look like clutter because the
if/elif/else bits line up, which fits the way Python has already
trained my brain.

> (Oh, and a way to decide between colon or no colon: we're not using
> colons in list comps and genexprs either.)

(grin) Easily fixed:

    print "average weight:", avg(for c in chefs: c.weight)
    rdict = dict(for k, v in D.iteritems(): v, k)

Honestly, I think I would prefer this syntax.  Examples from real
code, before and after:

    lines = [line for line in pr.block.body
             if line.logical_line.strip() != '']
    lines = [for line in pr.block.body:
                 if line.logical_line.strip() != '':
                     line]

    row.values = \
	[line[col.start:col.end].strip() for col in columns]
    row.values = \
	[for col in columns: line[col.start:col.end].rstrip()]

    return [p for p in self.listdir(pattern) if p.isdir()]
    return [for p in self.listdir(pattern): if p.isdir(): p]

-j