Python中 传递值 和 传递引用 的区别解析

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 headdef 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()