On 12/16/2010 5:44 AM, BartC wrote: >> 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. > > And you can't tell what the overall effect on a program will be: perhaps > the loop will be in a library function , which might be called billions > of times.
It might. But if the code it is calling does *anything* at all significant I can promise you that spending an extra 30% purely on the looping construct will still make a negligible difference to a program's execution time, and there are almost certainly going to be many other aspects of performance that will yield greater benefits from tuning. I realise that there are going to be some people who just flatly say "since 'while 1:' is quicker I am going to use it every time", and that their programs will still work. And I still maintain that (for English speakers) "while True:" is to be preferred. shol...@lifeboy ~ $ python -m timeit -- "i = 1" "while True:" " i += 1" " if i == 1000000: break" 10 loops, best of 3: 157 msec per loop shol...@lifeboy ~ $ python -m timeit -- "i = 1" "while True:" " i += 1" " if i == 1000000: break" " x = i+1" 10 loops, best of 3: 238 msec per loop shol...@lifeboy ~ $ python -m timeit -- "i = 1" "while 1:" " i += 1" " if i == 1000000: break" 10 loops, best of 3: 116 msec per loop shol...@lifeboy ~ $ python -m timeit -- "i = 1" "while 1:" " i += 1" " if i == 1000000: break" " x = i+1" 10 loops, best of 3: 195 msec per loop If binding a simple arithmetic expression adds more to the loop than the difference between "while 1:" and "while True:" you are wasting your time thinking about the savings under all but the most rigorous circumstances. Fortunately there is no penalty for ignoring my advice. regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 PyCon 2011 Atlanta March 9-17 http://us.pycon.org/ See Python Video! http://python.mirocommunity.org/ Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
