[Python-Dev] chained assignment weirdity

[Guido van Rossum]

The dict display is considered an *expression* and thus must follow
the L2R rule. The assignment is explicitly covered by the R2L rule for
assignments (only). Weird or not, those are the rules, and I don't
want to change them.

On Wed, Nov 7, 2012 at 1:39 PM, Ned Batchelder <ned at nedbatchelder.com> wrote:
>
> On 11/7/2012 12:08 PM, Serhiy Storchaka wrote:
>
> On 07.11.12 17:12, Nick Coghlan wrote:
>
> 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 :)
>
>
> Not only to dict comprehensions, but also to item assignments.  It will be
> weird if a dict comprehension and a plain loop will be inconsistent.
>
>
> Just to be clear: the reference guide says that the behavior *SHOULD BE*
> (but is not yet) this:
>
> Python 3.3.0
>>>> {print("a"):print("b")}
> a
> b
> {None: None}
>>>> d = {}
>>>> d[print("a")] = print("b")
> b
> a
>>>>
>
> Is this or is this not "weird" to you?
>
> --Ned.
>
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-- 
--Guido van Rossum (python.org/~guido)