On 6/5/2022 1:22 PM, Benedict Verhegghe wrote:
Op 5/06/2022 om 18:47 schreef David Mertz, Ph.D.:
Sure, that's nice enough code and has the same big-O complexity. I
suspect set difference is a little faster (by a constant multiple)
because it hits C code more, but I haven't benchmarked.
The OP said the elements were from fnmatch though, which explicitly
does not promise order. So really it's just whether you like your
code or this better aesthetically:
list(set(b) - set(a))
I benchmarked it and indeed the list difference is a little faster.
>>> timeit.timeit('s=set(b); [x for x in a if x not in s]', setup='a =
list(range(10000)); b = list(range(1000))', number=1000)
0.6156670850032242
>>> timeit.timeit('list(set(a)-set(b))', setup='a =
list(range(10000)); b = list(range(1000))', number=1000)
0.43649216600169893
And what's more, it seems to also preserve order. I guess because a
set is implemented like a dict, and will preserve order of you only
remove some elements from the set.
A set doesn't guarantee order at all, and indeed it does not preserve
creation order:
>>> s = set([10, 20, 1])
>>> s
{1, 10, 20}
You're seeing an accidental byproduct of the implementation.
Eric
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