list index()
Steve Holden
steve at holdenweb.com
Fri Aug 31 14:26:53 EDT 2007
Alex Martelli wrote:
> mensanator at aol.com <mensanator at aol.com> wrote:
> ...
>> Why wouldn't "the one obvious way" be:
>>
>> def inAnotB(A, B):
>> inA = set(os.listdir(A))
>> inBs = set(os.listdir(B))
>> return inA.difference(inBs)
>
> If you want a set as the result, that's one possibility (although
> possibly a bit wasteful as you're building one more set than necessary);
> I read the original request as implying a sorted list result is wanted,
> just like os.listdir returns (possibly sorted in case-independent order
> depending on the underlying filesystem). There's no real added value in
> destroying inA's ordering by making it a set, when the list
> comprehension just "naturally keeps" its ordering.
>
As I had reason to point out in another thread only recently,
os.listdir() makes no promises about the filename ordering.
Nevertheless I agree with you that the list comprehension method is the
obvious way to solve the problem, and the set optimization is just that.
regards
Steve
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