[Python-Dev] chained assignment weirdity

Guido van Rossum guido at python.org
Wed Nov 7 16:17:41 CET 2012

Ok, somebody go for it! (Also please refer to my pronouncement in the bug
-- I've gotta run.)

On Wed, Nov 7, 2012 at 7:12 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On Thu, Nov 8, 2012 at 12:54 AM, Guido van Rossum <guido at python.org>
> wrote:
> > On Wed, Nov 7, 2012 at 4:13 AM, Ned Batchelder <ned at nedbatchelder.com>
> wrote:
> >> If the bug report is accurate, CPython and the reference manual have
> >> disagreed since Python 2.5, and many of us are now surprised to hear it,
> >> which means there can't have been much broken code.
> >
> > Give that it was discussed before and fixed before, I think the intent
> > is clear: we should fix the code, not the docs.
> Almost certainly, it was broken in the migration to the AST compiler
> and there was no regression test to pick up the change.
> > I haven't looked at the proposed fixes, but I think correctness is
> > more important than saving an extra bytecode (OTOH keeping the set of
> > opcodes the same trumps both). I can't imagine that this extra opcode
> > will be significant in many cases.
> Since you've indicated the implementation is in the wrong here and you
> also want to preserve opcode semantics, I think Skip's patch is
> correct, but also needs to be applied to dict comprehensions (now we
> have them). The extra bytecode is only ROT_TWO, which is one of the
> cheapest we have kicking around :)
> Cheers,
> Nick.
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

--Guido van Rossum (python.org/~guido)
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