while True or while 1

[Steve Holden]

On 12/12/2010 2:32 PM, Christian Heimes wrote:
> Am 12.12.2010 19:31, schrieb Steve Holden:
>> > Would you care to quantify how much CPU time that optimization will
>> > typically save for a loop of fair magnitude (say, a billion iterations)?
> The difference is minimal but measurable for very tight loops.
> 
> $ python -m timeit -n20 -- "i = 0" "while 1:" "    i+=1" "    if i ==
> 1000000: break"
> 20 loops, best of 3: 89.7 msec per loop
> $ python -m timeit -n20 -- "i = 0" "while True:" "    i+=1" "    if i ==
> 1000000: break"
> 20 loops, best of 3: 117 msec per loop
> 
> In Python 2.x the peep hole optimizer can't remove the global lookup and
> check for trueness for "while True".
> 
Yes, you said that already and I certainly didn't disagree.

[...]

>> Python is designed to provide readable code. Writing
>> > 
>> >     while True:
>> >         ...
>> > 
>> > is much more legible than its pre-True couterpart
>> > 
>> >     while 1:
>> >         ...
> No argue with that! I was merely making a point that "while 1" executes
> different byte code than "while True". Readability is important but
> sometimes speed is of the essence. "while 1" is one of the few tricks to
> speed up tight loops a bit.

OK, but the figures you quote save you 27.3 ms per million iterations,
for a grand total saving of 27.3 ns per iteration. So "a bit" is hardly
worth considering for most programs, is it?

regards
 Steve
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