what does 'a=b=c=[]' do

[rusi]

On Dec 23, 6:10 pm, Robert Kern <robert.k... at gmail.com> wrote:
> On 12/23/11 10:22 AM, rusi wrote:
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> > On Dec 23, 2:39 pm, Steven D'Aprano<steve
> > +comp.lang.pyt... at pearwood.info>  wrote:
> >> On Fri, 23 Dec 2011 00:38:07 -0800, rusi wrote:
> >>> Likewise function arguments that default to mutable entities is a known
> >>> gotcha of python which is best treated as a bug in python.
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> >> Nonsense. It is a feature, not a bug.
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> > Tsk Tsk How can python have a bug? And that too on the python mailing
> > list?
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> > Others however feel differently. See Chris Rebert's
> >http://mail.python.org/pipermail/python-ideas/2007-January/000073.html
> > and the links cited there.
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> >> Some people might argue that it is a mistake, a minor feature which
> >> allegedly causes more difficulties than benefits. I do not hold with that
> >> idea. But either way, it is not a bug to be fixed, but a deliberate
> >> consequence of intended semantics.
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> > I did not ask or imply that it should be 'fixed', just that language
> > misfeatures should be treated with extra care.
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> "Bug" means, roughly, "something that should be fixed" not just any "thing that
> has some unwanted consequences". So yes, by calling it a bug you are asking and
> implying just that. If you don't mean that, don't use the word "bug".

Of course it should be fixed.  The repeated recurrence of it as a
standard gotcha as well as the python ideas list testifies to that.

Its not going to be fixed -- does not mean thats ideal, just that the
best proposed solutions cost/benefit equations are not good enough at
this point.

Case in point: I think it was around python 2.2 that there were
discussions for having a conditional operator.  GvR did not put it in
for a couple of releases not because it was a bad idea but because no
syntax was good enough.

When he finally did it, he chose a syntax which is arguably not ideal
but is the best all-things-considered (eg no unnecessary new keywords,
compatibility with existing code etc)