lst = [1, 2, 3]
for i, x in enumerate(lst):
     lst[i]=x*2

def list_function(x):
    x[:] = [i * 2 for i in x]
    return x

map(sum, zip(* [x]*2))

>>> a = [1, 2, 3]
>>> print map((2).__mul__, a)
[2, 4, 6]