is None or == None ?

[Rhodri James]

On Tue, 10 Nov 2009 18:55:25 -0000, Steven D'Aprano  
<steve at remove-this-cybersource.com.au> wrote:

> On Tue, 10 Nov 2009 15:46:10 +0000, Grant Edwards wrote:
>
>> On 2009-11-10, Rhodri James <rhodri at wildebst.demon.co.uk> wrote:
>>> On Sun, 08 Nov 2009 19:45:31 -0000, Terry Reedy <tjreedy at udel.edu>
>>> wrote:
>>>
>>>> I believe the use of tagged pointers has been considered and so far
>>>> rejected by the CPython developers. And no one else that I know of has
>>>> developed a fork for that. It would seem more feasible with 64 bit
>>>> pointers where there seem to be spare bits. But CPython will have to
>>>> support 32 bit machines for several years.
>>>
>>> I've seen that mistake made twice (IBM 370 architecture (probably 360
>>> too, I'm too young to have used it) and ARM2/ARM3).  I'd rather not see
>>> it a third time, thank you.
>>
>> MacOS applications made the same mistake on the 68K.  They reserved the
>> high-end bits in a 32-bit pointer and used them to contain
>> meta-information.
>
>
> Obviously that was their mistake. They should have used the low-end bits
> for the metadata, instead of the more valuable high-end.

Oh, ARM used the low bits too.  After all, instructions were 4-byte  
aligned, so the PC had all those bits going spare...

-- 
Rhodri James *-* Wildebeest Herder to the Masses