在Python之前引用的局部变量

Local variable referenced before Python

我有以下代码：

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def popLast(aLinkedList):
ptr = aLinkedList
while ptr != None:
if ptr['next']['next'] == None and ptr['next'] != None:
del_node = ptr['data']
ptr['next'] = ptr['next']['next']
ptr = ptr['next']

return (del_node,ptr)

当我放

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myLinkedList = createList(['a', 'b', 0, [1, 2]])
for i in range(getLength(myLinkedList)):
(a, myLinkedList) = popLast(myLinkedList)
print(a, end =", new list:")
printList(myLinkedList)

它一直在给我

UnboundLocalError: local variable 'del_node' referenced before assignment

当我只使用popLast(myLinkedList)时，没有问题。一切正常。我不知道是不是因为我的返回元组有问题。