교수님 ppt에 있는 코드를 복사하여 실행했는데 while문에서 'str' object has no attribute 'isTail' 에러가 발생했습니다. 제가 실행한 코드를 바탕으로 어느 부분에서 잘못 됐는지 알려주시면 감사하겠습니다.

class Node:
 nodeNext = ''
 objValue = ''
 blnHead = False
 blnTail = False
def __init__(self, objValue='', nodeNext = '', blnHead = False, blnTail = False):
 self.nodeNext = nodeNext
 self.objValue = objValue
 self.blnTail = blnTail 
 self.blnHead = blnHead
def getValue(self):
 return self.objValue
def setValue(self, objValue):
 self.objValue = objValue
def getNext(self):
 return self.nodeNext 
def setNext(self, nodeNext):
 self.nodeNext = nodeNext
def isHead(self):
 return self.blnHead
def isTail(self):
 return self.blnTail

node1 = Node(objValue='a')
nodeTail = Node(blnTail = True)
nodeHead = Node(blnHead = True, nodeNext = node1)

class SinglyLinkedList:
 nodeHead = ''
 nodeTail = ''
 size = 0
def __init__(self):
 self.nodeHead = Node(blnHead = True, nodeNext = self.nodeTail)
 self.nodeTail = Node(blnTail = True)

def insertAt(self, objInsert, idxInsert): 
 nodeNew = Node(objValue = objInsert) 
 nodePrev = self.get(idxInsert - 1) 
 nodeNext = nodePrev.getNext() 
 nodePrev.setNext(nodeNew) 
 nodeNew.setNext(nodeNext)
 self.size = self.size + 1

def removeAt(self, idxRemove):
 nodePrev = self.get(idxRemove - 1)
 nodeRemove = nodePrev.getNext()
 nodeNext = nodeRemove.getNext()
 nodePrev.setNext(nodeNext)
 self.size = self.size - 1
 return nodeRemove.getValue()

def get(self, idxRetrieve):
 nodeReturn = self.nodeHead # (nodeTail, '', False, True)
 for itr in range(idxRetrieve + 1):
  nodeReturn = nodeReturn.getNext() # nodeReturn(nodeHead's next node) = nodeTail
 return nodeReturn # nodeHead ('a', 0)

def printStatus(self):
 nodeCurrent = self.nodeHead
 while nodeCurrent.getNext().isTail() == True: # nodeHead.getNext() -> nodeNew reference.isTail()
  nodeCurrent = nodeCurrent.getNext()
  print(nodeCurrent.getValue(), end=" ")
 print("")

def getSize(self):
 return self.size

list1 = SinglyLinkedList()
list1.insertAt('a', 0)
list1.insertAt('b', 1)
list1.insertAt('d', 2)
list1.insertAt('e', 3)
list1.insertAt('f', 4)
list1.printStatus()

list1.insertAt('c', 2)
list1.printStatus()

list1.removeAt(3)
list1.printStatus()