Speed-up for loops

Gabriele Lanaro gabriele.lanaro at gmail.com
Sun Sep 5 00:54:14 CEST 2010


Maybe for the simple sum you can just use the sum builtin:
python -m timeit -s  'sum((10,)*10000)'
10000000 loops, best of 3: 0.0985 usec per loop

About the loop in general it's a good practice to use list comprehension and
generator expressions

2010/9/2 Michael Kreim <michael at perfect-kreim.de>

> Hi,
>
> I was comparing the speed of a simple loop program between Matlab and
> Python.
>
> My Codes:
> $ cat addition.py
> imax = 1000000000
> a = 0
> for i in xrange(imax):
>    a = a + 10
> print a
>
> $ cat addition.m
> imax = 1e9;
> a = 0;
> for i=0:imax-1
>    a = a + 10;
> end
> disp(a);
> exit;
>
> The results look like this:
> $ /usr/bin/time --verbose python addition.py
> 10000000000
>        Command being timed: "python addition.py"
>        User time (seconds): 107.30
>        System time (seconds): 0.08
>        Percent of CPU this job got: 97%
>        Elapsed (wall clock) time (h:mm:ss or m:ss): 1:50.09
>        [...]
>
> $ /usr/bin/time --verbose matlab -nodesktop -nosplash -r "addition"
> [...]
>    1.0000e+10
>        Command being timed: "matlab -nodesktop -nosplash -r addition"
>        User time (seconds): 7.65
>        System time (seconds): 0.18
>        Percent of CPU this job got: 94%
>        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:08.25
>        [...]
>
> Unfortunately my Python Code was much slower and I do not understand why.
>
> Are there any ways to speed up the for/xrange loop?
> Or do I have to live with the fact that Matlab beats Python in this
> example?
>
> Thanks a lot for your answers.
>
> With best regards,
>
> Michael
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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