is None or == None ?

Steven D'Aprano steven at
Wed Nov 11 04:07:36 CET 2009

On Tue, 10 Nov 2009 16:05:01 -0800, Vincent Manis wrote:

> At the time the 32-bit Macs were about to come on the market, I saw an
> internal confidential document that estimated that at least over 80% of
> the applications that the investigators had looked at (including many
> from that company named after a fruit, whose head office is on Infinite
> Loop) were not 32-bit clean. This in spite of the original edition of
> Inside Mac (the one that looked like a telephone book) that specifically
> said always to write 32-bit clean apps, as 32-bit machines were expected
> in the near future.

That is incorrect. The original Inside Mac Volume 1 (published in 1985) 
didn't look anything like a phone book. The original Macintosh's CPU (the 
Motorola 68000) already used 32-bit addressing, but the high eight pins 
were ignored since the CPU physically lacked the pins corresponding to 
those bits.

In fact, in Inside Mac Vol II, Apple explicitly gives the format of 
pointers: the low-order three bytes are the address, the high-order byte 
is used for flags: bit 7 was the lock bit, bit 6 the purge bit and bit 5 
the resource bit. The other five bits were unused.

By all means criticize Apple for failing to foresee 32-bit apps, but 
criticizing them for hypocrisy (in this matter) is unfair. By the time 
they recognized the need for 32-bit clean applications, they were stuck 
with a lot of legacy code that were not clean. Including code burned into 


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