Why is my code faster with append() in a loop than with a large list?

[MRAB]

Dave Angel wrote:
[snip]
> It would probably save some time to not bother storing the zeroes in the 
> list at all.  And it should help if you were to step through a list of 
> primes, rather than trying every possible int.  Or at least constrain 
> yourself to odd numbers (after the initial case of 2).
> 
Or stop looking for more factors when you've passed the square root of
num. I don't know what effect there'll be on the time if you recalculate
the square root when num changes (expensive calculation vs smaller
search space).