How this Python tree expression will be solve?

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Python

DSA

trees

I want to display the inorder, preorder, and postorder and also the value of the given expression Now inorder,postorder and preorder display successfully but value of give expression is not display and still give me error.

it give me error on line 95 which is last line and I also mentioned it in below.

print(eval_Tree(root))
NameError: name 'eval_Tree' is not defined

What I have tried:

class BST:
    def __init__(self, key):
        self.key = key
        self.lchild = None
        self.rchild = None

    def insert(self, data):
        if self.key is None:
            self.key = data
            return
        if self.key == data:
            return
        if data < self.key:
            if self.lchild:
                self.lchild.insert(data)
            else:
                self.lchild = BST(data)
        else:
            if self.rchild:
                self.rchild.insert(data)
            else:
                self.rchild = BST(data)

    def preorder(self):
        print(self.key, end=" ")
        if self.lchild:
            self.lchild.preorder()
        if self.rchild:
            self.rchild.preorder()

    def inorder(self):
        if self.lchild:
            self.lchild.inorder()
        print(self.key, end=" ")
        if self.rchild:
            self.rchild.inorder()

    def postorder(self):
        if self.lchild:
            self.lchild.postorder()
        if self.rchild:
            self.rchild.postorder()
        print(self.key, end=" ")

    def eval_Tree(root):
        if root is None:
            return 0
        if root.lchild is None and root.rchild is None:
            return float(self.key)
        left_sum = eval_Tree(root.lchild)

        # evaluate right tree
        right_sum = eval_Tree(root.rchild)

        # check which operation to apply
        if root.key == '+':
            return left_sum + right_sum

        elif root.key == '-':
            return left_sum - right_sum

        elif root.key == '*':
            return left_sum * right_sum

        else:
            return left_sum / right_sum


root = BST('+')
root.lchild = BST('/')
root.lchild.lchild = BST('*')
root.lchild.lchild.lchild = BST(0)
root.lchild.lchild.rchild = BST(0)
root.lchild.rchild = BST('-')
root.lchild.rchild.lchild = BST(9)
root.lchild.rchild.rchild = BST(0)
root.rchild = BST('*')
root.rchild.lchild = BST('+')
root.rchild.lchild.lchild = BST(1)
root.rchild.lchild.rchild = BST(1)
root.rchild.rchild = BST('/')
root.rchild.rchild.lchild = BST(0)
root.rchild.rchild.rchild = BST(1)

print("Preorder")
root.preorder()
print()
print("inorder")
root.inorder()
print()
print("postorder")
root.postorder()
print()
print("Value of Given expression IS ")
print(eval_Tree(root))