Re: Modifying every alternate element of a sequence

On 2006-11-28, jm.suresh@xxxxxxxxxxxxxxxxx <jm.suresh@xxxxxxxxx> wrote:
I have a list of numbers and I want to build another list with every
second element multiplied by -1.

input = [1,2,3,4,5,6]
wanted = [1,-2,3,-4,5,-6]

I can implement it like this:

input = range(3,12)
wanted = []
for (i,v) in enumerate(input):
if i%2 == 0:
wanted.append(v)
else:
wanted.append(-v)

But is there any other better way to do this.

Wether this is better, I'll leave that for others to decide. But this
is a possibility:

wanted = [ (1 - 2*(i%2)) * item for i, item in enumerate(input)]

--
Antoon Pardon
.