Is len O(n) or O(1) ?

[process]

Python uses arrays for lists right?

def quicksort(lista):
    if lista == []:
        lista
    else:
        return quicksort([x for x in lista[1:] if x < lista[0]]) +
[lista[0]] + \
               quicksort([x for x in lista[1:] if x >= lista[0]])

or

def quicksort(lista):
    if len(lista) == 0
        lista
    else:
        return quicksort([x for x in lista[1:] if x < lista[0]]) +
[lista[0]] + \
               quicksort([x for x in lista[1:] if x >= lista[0]])

wait first one raises TypeError unsupported operand types.