Python problem:

def f(l, a, b) :

l.append(a)

l = l + [b]

return l

x = [5, 9]

x = f(x, 2, 1) + x

From l.append(a) I got [5,9,2]

From l = l + [b] I got [5,9,2,1], and at here x = [5,9,2,1]

Thus f(x, 2, 1) + x is [5, 9, 2, 1, 5, 9, 2, 1] coz x is already been rewrite

But by python the result is [5, 9, 2, 1, 5, 9, 2] Why???