Beleg/bee

class Stack:  
    def __init__(self):  
        self.items = []  
          
    def isEmpty(self):  
        return len(self.items)==0   
      
    def push(self, item):  
        self.items.append(item)  
      
    def pop(self):  
        return self.items.pop()   
      
    def peek(self):  
        if not self.isEmpty():  
            return self.items[len(self.items)-1]  
          
    def size(self):  
        return len(self.items)
 
   
def postfixEval(postfixExpr):  
    operandStack = Stack()  
    tokenList =postfixExpr.split()  
   
    for token in tokenList:  
        if token in"0123456789":  
           operandStack.push(int(token))  
        else:  
            operand2 =operandStack.pop()  
            operand1 =operandStack.pop()  
            result =doMath(token,operand1,operand2)  
            operandStack.push(result)  
    return operandStack.pop()  
   
def doMath(op, op1, op2):  
    if op == "*":  
        return op1 * op2  
    elif op == "/":  
        return op1 / op2  
    elif op == "+":  
        return op1 + op2  
    else:  
        return op1 - op2  
   
print(postfixEval('7 8 + 3 2 + /'))