Design an Expression Tree With Evaluate Function

ExpressionTree.py

from typing import List

class TreeNode(object):

    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None
        return
        
    def evaluate(self) -> int:
        if self.val.isdigit():
            return int(self.val)
        elif self.val == "+":
            return self.left.evaluate() + self.right.evaluate()
        elif self.val == "-":
            return self.left.evaluate() - self.right.evaluate()
        elif self.val == "*":
            return self.left.evaluate() * self.right.evaluate()
        elif self.val == "/":
            return self.left.evaluate() // self.right.evaluate()
        else:
            pass

class TreeBuilder(object):
    @staticmethod
    def build(postfix: List[str]) -> TreeNode:
        stack = []
        for token in postfix:
            t = TreeNode(token)
            if not token.isdigit():
                t.right = stack.pop()
                t.left = stack.pop()
            stack.append(t)
        return stack.pop()
		
t = TreeBuilder.build(["3","4","+","2","*","7","/"])
print(t.evaluate()) # 2

t = TreeBuilder.build(["4","5","2","7","+","-","*"])
print(t.evaluate()) # -16

t = TreeBuilder.build(["4","2","+","3","5","1","-","*","+"])
print(t.evaluate()) # 18

t = TreeBuilder.build(["100","200","+","2","/","5","*","7","+"])
print(t.evaluate()) # 757