At 10:22 AM 8/24/2007, Kent Johnson wrote: >Dick Moores wrote: >>>>This time I added "xrange(10, end, 10)" and did the timing using >>>>the template in the timeit module: >>>>template = """ >>>>def inner(_it, _timer): >>>> _t0 = _timer() >>>> from itertools import chain >>>> end = 1000000 >>>> for _i in _it: >>>> for x in chain(xrange(1, end, 10), xrange(2, end, 10), >>>> xrange(3, end, 10), xrange(4, end, 10), xrange(5, end, 10), >>>> xrange(6, end, 10), xrange(7, end, 10), xrange(8, end, 10), >>>> xrange(9, end, 10), xrange(10, end, 10)): >>>> pass >>>> _t1 = _timer() >>>> return _t1 - _t0 >>>>""" >>>>This gets always close to 71 msec per loop. >>>> >>>>template = """ >>>>def inner(_it, _timer): >>>> _t0 = _timer() >>>> end = 1000000 >>>> for _i in _it: >>>> for x in xrange(end): >>>> pass >>>> _t1 = _timer() >>>> return _t1 - _t0 >>>>""" >>>>This gets always close to 84 msec per loop. >>>>So they're not the same! And yours is the faster one! Because >>>>itertools.chain() is written in C, I suppose. >>>That is very strange. I did a simple timer with time.time() and >>>found that my original (1-9) version was consistently a little >>>slower than the simple xrange(). And xrange is written in C too, >>>and the chain version adds a layer over xrange. You should check >>>your code carefully, that is a very surprising result. >>Yes, surprising. But the templates pasted above are exactly what I >>used in 2 copies of timeit.py. I don't know what to check. Can you >>see what's wrong? I just ran both of those again, with very similar results. > >So you actually pasted that code into timeit.py?
Yeah. :-( I think I learned on the Tutor list to do it that way, but I'm not sure. Thanks for showing me a correct way. >That is a pretty unconventional use of the module! I wonder if there >is something strange going on there? > >Using timeit more conventionally I get unsurprising results. This program: > >from timeit import Timer > >setup = 'from itertools import chain' >stmt = '''end = 1000000 >for x in chain(xrange(1, end, 10), xrange(2, end, 10), > xrange(3, end, 10), xrange(4, end, 10), xrange(5, end, 10), > xrange(6, end, 10), xrange(7, end, 10), xrange(8, end, 10), > xrange(9, end, 10), xrange(10, end, 10)): > pass >''' > >print min(Timer(stmt, setup=setup).repeat(number=10)) > >stmt = '''end = 1000000 >for x in xrange(end): > pass >''' > >print min(Timer(stmt).repeat(number=10)) > > >has output: >0.497083902359 >0.359513998032 > >which is more in line with what I would expect. Using your exact code, I just got 0.737564690484 1.17399585702 Which is the reverse of your result, but on a slower computer. What's up with that?? >I can't account for the variations between different timing methods. Dick _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
