while True or while 1

[Ethan Furman]

BartC wrote:
> "Steve Holden" <steve at holdenweb.com> wrote in message 
> news:mailman.462.1292214062.2649.python-list at python.org...
>> On 12/12/2010 2:32 PM, Christian Heimes wrote:
>>> Am 12.12.2010 19:31, schrieb Steve Holden:
>>> $ 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
> 
>>> 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?
> 
> One these is 30% faster than the other. That's an appreciable 
> difference, which you can't really just dismiss.

Anecdotal evidence says it is easily dismissed:

I had a routine that processed records from a table using custom, on the 
fly, code.  I could either use exec for each record to do the work, or 
create a function that would then be called.  I timed exec vs function, 
and found the function style to be about 200% faster... Eureka!, I 
thought.  After putting the functional method in place, a run that took 
about 16 minutes using the old exec method ran two (2!) seconds faster.

Great learning experience, for both the function method (which I 
prefer), and the need for profiling.


~Ethan~