def double(lst):# hey this is destructive!
    for i in range(len(lst)):
        lst[i] = lst[i] * 2
    print("lst:", lst)
    return None

x = [1, 2, 3]
print("Result:", double(x))
print("x:", x)

###

# Non-destructive
def double(lst):
    result = [ ]
    for i in range(len(lst)):
        result.append(lst[i] * 2)
    return result

y = [1, 2, 3]
print("Result:", double(y))
print("y:", y)