Possible Duplicate:
What does += mean in Python?
I have a def function looks like:
def s(xs, n, m):
    t = []
    while n < m:
        t.append(xs[n])
        n += 2
    return t
I understand the above code by t.append(xs[n]), but have no idea what n += 2 means here.
Any help will be appreciated. Thanks
 
     
    