class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

if __name__ == '__main__':  
    linklist = dummy = ListNode()    
    for x in ([2,4,3]): 
        linklist .next = ListNode(x) 
        linklist = linklist .next
    while dummy:
        print(dummy.val)
        dummy = dummy.next

这里的dummy 相当于是游标，每次使用链表都要单独创建一个游标指向链表头，不要直接使用链表，否则链表无法重新指向头结点

头结点默认为0

如果不要头结点0，可以像这样写

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

if __name__ == '__main__':  
    linklist = dummy = ListNode()    
    for x in ([2,4,3]): 
        linklist .next = ListNode(x) 
        linklist = linklist .next
    no_head = dummy.next
    while no_head:
        print(no_head.val)
        no_head = no_head.next