Leo Kislov: > input[1::2] = [-item for item in input[1::2]] > If you don't want to do it in-place, just make a copy: > wanted = input[:] > wanted[1::2] = [-item for item in wanted[1::2]]
Very nice solution. I have tried few versions like: from itertools import imap, islice from operator import neg 1) data[1::2] = [-el for el in data[1::2]] 2) data[1::2] = map(neg, data[1::2]) 3) data[1::2] = imap(neg, data[1::2]) 4) data[1::2] = map(neg, islice(data, 1, None, 2)) 5) etc. With Python 2.5 it seems that the n.2 (map + slicing) is the faster. Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
