swap nodes in pairs

def swapPairs(self, head):
        if head == None or head.next == None:
            return head
        first,second = head,head.next
        while second != None:
            first.next = second.next
            second.next = first
            if first == head:
                head = second
                last = first
            else:
                last.next = second
            last = first
            first = first.next
            if first != None:
                second = first.next
            else:
                break
        return head