[Python-Dev] New syntax for 'dynamic' attribute access

[Guido van Rossum]

On 2/12/07, Maric Michaud <maric at aristote.info> wrote:
> Le mardi 13 février 2007 01:36, Barry Warsaw a écrit:
> > On Feb 12, 2007, at 7:32 PM, Guido van Rossum wrote:
> > > Oh, now I am definitely in favor of .[]! I read it in gmail in FireFox
> > > which uses a small variable-pitch font whose dot is a single pixel.
> > > The .() example was hard to find; the .[] jumped out immediately.
> > > (When do you ever see self[anything]?)
> >
> > Raymond's -> suggestion was nice.
> >
> I really dislikes the .[ or .( or .{ operators.
> Just on my mail editor the two expressions
>
> a.[b]
>
> and
>
> a,[b]
>
> are quite hard to differentiate while completely unrelated.

Yeah, so are 1.2 and 1,2. This is why the style guide (PEP 8) insists
on a space after a comma but not after a period.

> Why did the brace syntax wasn't even discussed ? Seems clean to me.

Because they are arbitrary -- if x{y} or x.{y} would be acceptable,
why not x.<y> or x.|y| or x./y/? Or indeed why not x at y? (Not that I'm
in favor of that. :-)

That x.[y] and x.(y) resemble x[y] and x(y) is an *advantage* of the
proposed new notation, not a disadvantage; the new operator is
semantically closer to x[y] than to x(y) so x.[y] makes sense.

> obj{expr} can be read as "given obj as a namespace, retrieve the name
> resulting by expr in obj and enclosing namespaces (supers)".

Yeah, it can just as well be read as "call obj with 2**expr as
argument". Also, your reference to enclosing namespaces and supers is
misplaced -- this should map to the existing __getattr__ operation,
which can have many different semantics depending on the type of obj.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)