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 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()