Re: How to increase the speed of this program?


Peter Otten wrote:
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.


I'm extremely agnostic about the spelling :-) IOW I'd be very glad of
any way [pure Python; e.g. maintaining my own version of the array
module doesn't qualify] to simply and rapidly create an array.array
instance with typecode t and number of elements n with each element
initialised to value v (default to be the zero appropriate to the
typecode).

Cheers,
John

.

Relevant Pages

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  • Re: How to increase the speed of this program?
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