Lucky numbers in Python

Cecil Westerhof Cecil at
Thu Apr 30 08:34:26 CEST 2015

Op Thursday 30 Apr 2015 04:55 CEST schreef Ian Kelly:

> On Wed, Apr 29, 2015 at 6:01 PM, Cecil Westerhof <Cecil at> wrote:
>> Op Thursday 30 Apr 2015 00:38 CEST schreef Ian Kelly:
>>> In that case you can definitely omit the middle term of the slice,
>>> which will be both more concise and clearer in intent, though
>>> probably not significantly faster.
>> It is certainly nit faster. It is even significantly slower. With
>> the middle term lucky_numbers(int(1e6)) takes 0.13 seconds. Without
>> it takes 14.3 seconds. Hundred times as long.
> That would be rather surprising, since it's the same operation being
> performed, so I did my own timing and came up with 0.25 seconds
> (best of 3) with the middle term and 0.22 seconds without.
> I suspect that you tested it as "del sieve[skip_count - 1 :
> skip_count]" (which would delete only one item) rather than "del
> sieve[skip_count - 1 :: skip_count]".

Yeah, that is how I interpreted omitting the middle term. But it
seemed to give the right results.

With your amendment it runs slightly faster. With 1E7 it is 8.0 and
7.7. So almost 4% faster.

Cecil Westerhof
Senior Software Engineer

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