On Feb 21, 2020, at 00:46, Steven D'Aprano <st...@pearwood.info> wrote:
>
>
> Got some actual measurements to demonstrate that initialising the array
> is a bottleneck? Especially for something as small as 64, it seems
> unlikely. If it were 64MB, that might be another story.
>
> What's wrong with `array.array("i", [0])*64` or equivalent?
>
> On my machine, at least, constructing a bytes object first followed by
> an array is significantly faster than the alternative:
>
> [steve@ando cpython]$ ./python -m timeit -s "from array import array"
> "array('i', bytes(500000))"
> 100 loops, best of 5: 1.71 msec per loop
>
> [steve@ando cpython]$ ./python -m timeit -s "from array import array"
> "array('i', [0])*500000"
> 50 loops, best of 5: 7.48 msec per loop
>
> That surprises me and I cannot explain it.
Without reading the code, I can guess. The first one does two 500K allocations
and a 500K memcpy; the second only does one 500K allocation but does 150K
separate 4-byte copies, and the added cost of that loop and of not moving as
many bytes at a time as possible is higher than the savings of a 500K
allocation.
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