为什么我在尝试打印单链表中的元素时会得到这个永不结束的循环

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

def has_cycle(head):
    if head is None or head.next is None:
        return False
    
    slow = head
    fast = head.next
    
    while slow != fast:
        if fast is None or fast.next is None:
            return False
        slow = slow.next
        fast = fast.next.next
    
    return True

def print_linked_list(head):
    if head is None:
        return
    
    current = head
    while current is not None:
        print(current.val)
        current = current.next

# 创建一个有循环的链表
node1 = ListNode(1)
node2 = ListNode(2)
node3 = ListNode(3)
node4 = ListNode(4)
node5 = ListNode(5)

node1.next = node2
node2.next = node3
node3.next = node4
node4.next = node5
node5.next = node2  # 循环引用

if has_cycle(node1):
    print("链表中存在循环")
else:
    print("链表中不存在循环")

# 打印链表元素（注意：如果链表中存在循环，将陷入无限循环）
print_linked_list(node1)