How to increase the speed of this program?

Peter Otten __peter__ at web.de
Tue Nov 28 10:55:15 CET 2006


Peter Otten wrote:

> Leo Kislov wrote:
> 
>> 
>> Peter Otten wrote:
>>> Peter Otten wrote:
>>>
>>> > HYRY wrote:
>>> >
>>> >> I want to join two mono wave file to a stereo wave file by only using
>>> >> the default python module.
>>> >> Here is my program, but it is much slower than the C version, so how
>>> >> can I increase the speed?
>>> >> I think the problem is at line #1, #2, #3.
>>> >
>>> >> oarray = array.array("h", [0]*(len(larray)+len(rarray))) #1
>>> >
>>> > ITEMSIZE = 2
>>> > size = ITEMSIZE*(len(larray) + len(rarray))
>>> > oarray = array.array("h")
>>> > oarray.fromstring("\0" * size)
>>> >
>>> > may be a bit faster.
>>>
>>> Confirmed:
>>>
>>> $ python2.5 -m timeit -s'from array import array; N = 10**6' 'a =
>>> array("h"); a.fromstring("\0"*(2*N))'
>>> 100 loops, best of 3: 9.68 msec per loop
>>> $ python2.5 -m timeit -s'from array import array; N = 10**6' 'a =
>>> array("h",
>>> [0]*N);'
>>> 10 loops, best of 3: 199 msec per loop
>> 
>> Funny thing is that using huge temporary string is faster that
>> multiplying small array:
>> 
>> C:\Python25>python -m timeit -s"from array import array; N = 10**6" "a
>> =array('h'); a.fromstring('\0'*(2*N))"
>> 100 loops, best of 3: 9.57 msec per loop
>> 
>> C:\Python25>python -m timeit -s"from array import array; N = 10**6" "a
>> = array('h','\0\0'); a*N"
>> 10 loops, best of 3: 28.4 msec per loop
>> 
>> Perhaps if array multiplication was as smart as string multiplication
>> then array multiplication version would be the fastest.

Oops, I have to work on my reading skills. You're right, of course...

> That will not suffice:
> 
> $ python2.5 -m timeit -s'from array import array; from itertools import
> repeat; N = 10**6; init = [0]*N' 'array("h", init)'
> 10 loops, best of 3: 130 msec per loop
> 
> $ python2.5 -m timeit -s'from array import array; from itertools import
> repeat; N = 10**6; init = "\n"*(2*N)' 'array("h").fromstring(init)'
> 100 loops, best of 3: 5 msec per loop
> 
> A big chunk of the time is probably consumed by "casting" the list items.
> Perhaps an array.fill(value, repeat) method would be useful.

... and that could be spelled array.__mul__ as you suggest.

Peter




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