On Feb 11, 8:22 pm, Basilisk96 <basilis...@gmail.com> wrote:
> Hello all,
>
> I have the following function that uses an intermediate iterator
> "rawPairs":
>
> def MakePairs(path):
> import os
> import operator
> join = os.path.join
> rawPairs = (
> (join(path, s), func(s))
> for s in os.listdir(path)
> if func(s) is not None and func(s).endswith("some criterion")
> )
> #Use the second item in the pair as the sort criterion
> result = sorted(rawPairs, key=operator.itemgetter(1))
> return result
>
> where "func" is a single-argument function that returns either a
> string or None, but is an expensive call.
> I am pretty sure that the sorted() construct cannot be improved much
> further, but...
> ...does anyone have ideas on improving the "rawPairs" iterator so that
> it calls "func(s)" only once per iteration? Perhaps a lambda
> construct, but I am not sure how to go about it...?
>
> Cheers,
> Basilisk96
Hi,
Try something like this:
import os
from os.path import join
from itertools import ifilter #assuming 2.5 and earlier, for 3.0 just
use the filter builtin
from operator import itemgetter
def isvalid(pair):
return (s[1] is not None) and s[1].endswith('some criteria')
def makepairs(path):
pair_iter = ((join(path,s), func(s)) for s in os.listdir(path))
pair_iter = ifilter(isvalid, pair_iter)
result = sorted(pair_iter, key=itemgetter(1))
return result
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