Python中 传递值 与 传递引用 的区别

class NodeList(object):
    def __init__(self, val):
        self.val = val
        self.next = None

# 遍历链表
def traverse_nodes(head):

    tmp = head
    while tmp:
        print("节点id为:", id(tmp), "节点的值为:", tmp.val, )
        tmp = tmp.next

# 创建链表
def create_node_list():

    head = NodeList(0);
    left_p = head
    print("头节点id:",id(head), "当前节点id:",id(left_p), "当前节点值:", left_p.val)

    left_p.next = NodeList(1);
    left_p = left_p.next
    print("头节点id:",id(head), "当前节点id:",id(left_p), "当前节点值:", left_p.val)    

    left_p.next = NodeList(2);
    left_p = left_p.next
    print("头节点id:",id(head), "当前节点id:",id(left_p), "当前节点值:", left_p.val)

    left_p.next = NodeList(3);
    left_p = left_p.next
    print("头节点id:",id(head), "当前节点id:",id(left_p), "当前节点值:", left_p.val)

    return head

def main():
    # 创建链表
    print("==>创建链表函数中:")
    head = create_node_list()

    print("==>在遍历函数中:")
    traverse_nodes(head)

if __name__ == '__main__':
    main()