[Python] doubly Linked list iterator python

I am constructing a doubly linked list and I am struggling on construct a doubly linked list iterator method in PYTHON.

This is my code so far

class DoubleListNode:
def __init__(self,data):
self.data=data
self.prev = None
self.next= None

class ListIterator:
def __init__(self):
self._current = self.head

def __iter__(self):
return self

def next(self):
if self.size == 0 :
raise StopIteration
else:
item = self._current.data
self._current=self._current.next
return item

class DoublyLinkedList:
def __init__(self):
self.head= None
self.tail= None
self.size = 0

def add(self,data):
newnode= DoubleListNode(data)
self.size+=1
if self.head is None:
self.head = newnode
self.tail = self.head
elif data < self.head.data: # before head
newnode.next = self.head
self.head.prev= newnode
self.head= newnode
elif data > self.tail.data: # at the end
newnode.prev= self.tail
self.tail.next= newnode
self.tail=newnode
else:
curNode = self.head
while curNode is not None and curNode.data < data:
curNode=curNode.next
newnode.next= curNode
newnode.prev=curNode.prev
curNode.prev.next= newnode
curNode.prev=newnode

def remove(self,data):
curNode=self.head
while curNode is not None and curNode.data!= data:
curNode= curNode.next
if curNode is not None:
self.size -= 1
if curNode is self.head:
self.head= curNode.next
else:
curNode.prev.next=curNode.next
if curNode is self.tail:
self.tail=curNode.prev
else:
curNode.next.prev=curNode.prev


When I run a test it said TypeError: iteration over non-sequence. Did I do something wrong ?

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