出现了Attribute Error，请问怎么处理？语言- python

在写二叉树计算器时出现了AttributeError:NoneType object has no attribute'setRootVal'如图

错误行代码如下

请问应该怎么修改？

def BinaryTree(r):
    def __init__(self,rootObj):
        self.key = rootObj
        self.leftChild = None
        self.rightChild = None
    def inserttLeft(self,newNode):
        if self.leftChild == None:
            self.leftChild = BinaryTree(newNode)
        else:
            t = BinaryTree(newNode)
            t.leftChild = self.leftChild
            self.leftChild = t
    def insertRight(self,newNode):
        if self.rightChild == None:
            self.rightChild = BinaryTree(newNode)
        else:
            t = BinaryTree(newNode)
            t.rightChild = self.rightChild
            self.rightChild = t
    def getRightChild(self):
        return self.rightChild
    def getLeftChild(self):
        return self.leftChild
    def setRootVal(self,obj):
        self.key = obj
    def getRootVal(self):
        return self.key
def buildParseTree(fpexp):
    fplist = fpexp.split()
    pStack = Stack()
    eTree = BinaryTree('')
    pStack.push(eTree)
    currentTree = eTree
    for i in fplist:
        if i == '(':
            currentTree.insertLeft('')
            pStack.push(currentTree)
            currentTree = currentTree.getLeftChild()
        elif i not in ['+','-','*','/']:
            if not None:
                currentTree.setRootVal(int(i))
            parent = pStack.pop()
            currentTree = parent
        elif i in ['+','-','*','/']:
            currentTree.setRootVal(i)
            currentTree.insertRight('')
            pStack.push(currentTree)
            currentTree = currentTree.getRightChild()
        elif i == ')':
            currentTree = pStack.pop()
        else:
            raise ValueError
    return eTree

x = input()
buildParseTree(x)

原因
报错：AttributeError:NoneType object has no attribute'setRootVal'
意思是你里面有一个None也就是空值，但是你调用的它的setRootVal

解决方法
在你报错的第49行原先代码前多加个判断：

if not None:
   # 你的代码

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