[Pyobjc-dev] Re: [Python-Dev] PyBuffer* vs. array.array()

[Christian T. <ti...@ti...>]

Guido van Rossum wrote:
>>>I'm not sure if you were joking, but why not write
>>>
>>>         singlePlane.fromlist([0] * (width*height*3))
>>
>>  Or cheaper and faster for large width and height:
>>
>>           singlePlane = array.array('B', [0])*width*height*3
> 
> 
> Correct; then even better:
> 
>              singlePlane = array.array('B', [0]) * (width*height*3)
> 
> i.e. do only one sequence repeat rather than three.

For "large" widths and heights, like 1000*1000, this
effect is remarkably small: About 3 percent only.
The above is true for simple lists.

There are also counterexamples, where you are
extremely wrong (sorry), most probably due to
the mplementation, but also by the effect, that
medium sized flat objects can be copied more
efficiently than very small ones.

 >>> if 1:
... 	t = time.clock()
... 	for i in xrange(100):
... 		s = ' ' * 1000 * 1000
... 	print time.clock()-t
...
0.674784644417
 >>> if 1:
... 	t = time.clock()
... 	for i in xrange(100):
... 		s = ' ' * 1000000
... 	print time.clock()-t
...
6.28695295072
 >>>

Did I hear you head knocking on the keyborard?

ciao - chris
-- 
Christian Tismer             :^)   <mailto:ti...@ti...>
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