无法从单链接列表中删除

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

def deleteNode(head, val):
    # 处理头节点
    if head.val == val:
        return head.next
    
    # 遍历链表，找到待删除节点的前一个节点
    prev = head
    curr = head.next
    while curr:
        if curr.val == val:
            prev.next = curr.next
            curr = None
            break
        else:
            prev = curr
            curr = curr.next
    
    return head

# 示例用法
# 创建链表：1 -> 2 -> 3 -> 4 -> None
head = ListNode(1)
head.next = ListNode(2)
head.next.next = ListNode(3)
head.next.next.next = ListNode(4)

# 删除节点值为3的节点
head = deleteNode(head, 3)

# 打印链表：1 -> 2 -> 4 -> None
curr = head
while curr:
    print(curr.val)
    curr = curr.next