hashability

Chris Rebert clp2 at rebertia.com
Wed Aug 12 19:50:33 CEST 2009


On Wed, Aug 12, 2009 at 1:37 PM, James Stroud<jstroud at mbi.ucla.edu> wrote:
> Steven D'Aprano wrote:
>>
>> Well there you go -- why on earth would you prohibit None as a dictionary
>> key??? That's a serious failure.
>
>
> roentgen 1% python
> Python 2.5 (r25:51908, Sep 20 2006, 17:36:21) [GCC 3.4.2] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> py> hash(None)
> 135543872
>
>
> mbi136-176 98% /usr/bin/python
> Python 2.5.1 (r251:54863, Feb  6 2009, 19:02:12) [GCC 4.0.1 (Apple Inc.
> build 5465)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
> py> hash(None)
> 2030240

Actually, None is a special-case as a built-in singleton value --
there's only ever *exactly one* instance of it in a given interpreter
session. And I'm reasonably sure dict pickles don't store the hash
code of items (the dict gets recreated from scratch), so there's no
problem.

Cheers,
Chris
-- 
http://blog.rebertia.com



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