On Tue, 27 Oct 2009 04:36:12 +0000, John O'Hagan wrote:
> I sometimes use timeit to see if it's better to check if something needs
> doing, or to just do it anyway. This result was surprising:
>
> setup = 'd1 = {"a":0, "b":0}; d2 = {"a":0, "b":1}'
>
> Timer('d1.update(d2)', setup).timeit() 2.6499271392822266
>
> Timer('if d1 != d2: d1.update(d2)', setup).timeit() 1.0235211849212646
>
> In other words, in this case it's substantially quicker to check for
> something and then proceed, than it is to just proceed! I'm curious
> about the explanation.
The code snippet is executed inside a loop. The first snippet runs
d1.update(d2) one million times. The second snippet runs "if d1 != d2"
one million times, and d1.update(d2) once.
--
Steven
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