[Tutor] List comprehension question

[Steven D'Aprano]

Richard D. Moores wrote:

> def proper_divisors_sum(n):
>     return sum(list(divisors(n))) - n

There's no need to call list first. sum() will happily operate on any 
sort of iterable -- lists, sums, iterators, generators, range objects. 
Anything except strings, which would be pointless even if you could do 
it, which you can't, but even so you can fool sum() to work with strings 
with a bit of effort.


> Using Steven's suggested speed test
> this gets 6.2404818210135886
> 
> My up-to-now fastest version,
[...]
> gets 6.1753780857622473
> 
> So they're about even.

I'd say that the difference is probably statistically insignificant. 
Even if it's consistent on your PC, on another PC with a slightly 
different processor, slightly different memory, or a different operating 
system, it could very well go the other way.

In any case, since those times are ~6 seconds per 100,000 loops, the 
real difference is only 60 microseconds -- completely trivial unless 
you're doing some *serious* number crunching.


P.S. don't take that as a put down -- you should be pleased that your 
code is around as fast as Tim Peter's code :)


-- 
Steven