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+--- Thread: itertool islice why no negative values ? (/thread-23997.html)
itertool islice why no negative values ? - voidptr - Jan-26-2020
About itertool islice.
Why islice doesn't support negative values ?
( I realized than negative index need oftn the len() of something, it might need a complete generation of the list to get this, but for some generators and some different iterators might not ... )
Here my snippet, maybe someone can do better :)
(of course here im using a range, instead of some generators or iterators)
import itertools as it
def xislice(iterable, *args):
#xislice(coll,stop)
#xislice(coll,start,stop,[step])
#handle negative args
sz = len(args)
if sz == 0:
start = 0
stop = len(iterable)
step = 1
elif sz == 1:
start = 0
stop = args[0] if args[0] != None else len(iterable)
step = 1
elif sz == 2:
start = args[0] if args[0] != None else 0
stop = args[1] if args[1] != None else len(iterable)
step = 1
else:
start = args[0] if args[0] != None else 0
stop = args[1] if args[1] != None else len(iterable)
step = args[2] if args[2] != None else 1
for x in range(start, stop, step):
yield iterable[x]
xx = list(range(0,20))
yy = [x for x in it.islice(xx,1,None,2)]
print(yy)
yy = [x for x in xislice(xx,1,None,2)]
print(yy)
yy = [x for x in xislice(xx,15,-1,-2)]
print(yy)
#yy = [x for x in it.islice(xx,15,-1,-2)]
RE: itertool islice why no negative values ? - Gribouillis - Jan-27-2020
You might want to compare this with more_itertools.islice_extended()
RE: itertool islice why no negative values ? - voidptr - Jan-27-2020
Interesting, I didn't had the time to search for others implementations, but I will .
Thanks for the pointers :)