[EMAIL PROTECTED] 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. > > -- > Suresh
I would tend to do this as a list comprehension. In python 2.5 you can do this: wanted = [(v if i % 2 == 0 else -v) for (i,v) in enumerate(input)] (a if b else c) is new to Python 2.5. You don't always need the brackets, but I think it makes things clearer. See (http://docs.python.org/whatsnew/pep-308.html) for more details on this feature. With earlier versions, you could do wanted = [v - 2*(i % 2) for (i,v) in enumerate(input)] That looks less clear to me than your version, though. John Hicken -- http://mail.python.org/mailman/listinfo/python-list
