PEP308: Yet another syntax proposal

[Andrew Dalke]

James J. Besemer:
> Andrew Dalke wrote:
> > Raymond Hettinger
> >  ....
> > Err, that should have been
> >
> >     [ spelled out long-hand ]

> Now you're being unreasonable.

No, I'm not being unreasonable.  Raymond used

   data = isinstance(source, file)  ??   source.readlines()  ||
source.split()

My post was not commenting about the use of the ?? || syntax,
it was saying that explicit type checking should not be used for
this case.

Specifically, don't check for a file instance, check to see if it supports
a 'readlines'.  As written, it prevents me from using a StringIO class
or anything else which implements 'readlines.'

At best, do the type check only for the most restrictive case
(which is a string) rather than the least restrictive case (a file-like
object).

The fact that I wrote my objection using the traditional if/else has
nothing to do with the point of the matter.

> You were asked for an example where short-circuit would be necessary and
this
> is a well-intentioned, legitamet illustration.
>
> The fact (as you point out and WE ALL KNOW) that it can be rewritten the
> other way does not materially add to the discussion.

The test should have been, in his parlance,

   data = hasattr(source, "readlines")  ??   source.readlines()  ||
source.split()

Even with that case, I would rather not get that property twice,
so, using Alex's clarification of my example, the best solution is

  try:
    readlines = source.readlines
  except AttributeError:
    data = source.split()
  else:
    data = readlines()

Therefore, even though I was not really commenting on the use
of an if/else expression idiom, it happens that this example is not
legitamet .. legtiment,  .. legit-whatever.

                    Andrew
                    dalke at dalkescientific.com