sum() vs. loop
Dan Stromberg
drsalists at gmail.com
Mon Oct 11 23:41:35 EDT 2021
On Mon, Oct 11, 2021 at 2:54 PM Steve Keller <keller.steve at gmx.de> wrote:
> I have found the sum() function to be much slower than to loop over the
> operands myself:
>
> def sum_products(seq1, seq2):
> return sum([a * b for a, b in zip(seq1, seq2)])
>
> def sum_products2(seq1, seq2):
> sum = 0
> for a, b in zip(seq1, seq2):
> sum += a * b
> return sum
>
> In a program I generate about 14 million pairs of sequences of ints each
> of length 15 which need to be summed. The first version with sum() needs
> 44 seconds while the second version runs in 37 seconds.
>
> Can someone explain this difference?
>
I can't explain it. It might help to try a line-by-line profiler.
If you need speed, maybe try Cython, numpy and/or numba.
It seems like the generator expression should be the fastest to me. But
writing for speed instead of writing for clarity is usually not a great
idea.
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