is None or == None ?

Steven D'Aprano steve at
Tue Nov 10 19:55:25 CET 2009

On Tue, 10 Nov 2009 15:46:10 +0000, Grant Edwards wrote:

> On 2009-11-10, Rhodri James <rhodri at> wrote:
>> On Sun, 08 Nov 2009 19:45:31 -0000, Terry Reedy <tjreedy at>
>> 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.

High-end-is-always-better-right?-ly y'rs,


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