How to increase the speed of this program?

Peter Otten __peter__ at web.de
Tue Nov 28 10:50:26 CET 2006


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.

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.

Peter




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