Python 3000 idea: reversing the order of chained assignments

Steve Holden steve at holdenweb.com
Thu Mar 22 03:05:01 CET 2007


Virgil Dupras wrote:
> On Mar 21, 9:24 pm, Steve Holden <s... at holdenweb.com> wrote:
>> Marcin Ciura wrote:
>>> Steven D'Aprano wrote:
>>>>>>> x, y, z = 1, 2, 3
>>>>>>> x = y = z
>>>>>>> x, y, z
>>>> (3, 3, 3)
>>>> I certainly wouldn't expect to get (2, 3, 3).
>>> Neither would I. I must have expressed myself not clearly enough.
>>> Currently
>>> x = y = z
>>> is roughly equivalent to
>>> x = z
>>> y = z
>>> I propose to change it to
>>> y = z
>>> x = z
>>> Cheers,
>>>    Marcin
>> The difference being ... ?
>> --
>> Steve Holden       +44 150 684 7255  +1 800 494 3119
>> Holden Web LLC/Ltd          http://www.holdenweb.com
>> Skype: holdenweb    http://del.icio.us/steve.holden
>> Recent Ramblings      http://holdenweb.blogspot.com
> 
> I think I see what Marcin means. The 'node' is changed too fast in the
> chain, and next is assigned to 'nextnode' instead of being assigned to
> node.
> 
>>>> class Node:
> ...     pass
> ...
>>>> node = Node()
>>>> nextnode = Node()
>>>> backup_node = node
>>>> node = node.next = nextnode
>>>> node.next is node
> True
>>>> hasattr(backup_node,'next')
> False
> 
So we should take the already well-defined semantics of assignment and 
change them because it seems more obvious to J. Random User? I think I 
might be a little concerned about potential code breakage there.

regards
  Steve
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
Holden Web LLC/Ltd          http://www.holdenweb.com
Skype: holdenweb     http://del.icio.us/steve.holden
Recent Ramblings       http://holdenweb.blogspot.com




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