class Stack:
    def __init__(self):
        self.items = []

    def isEmpty(self):
        return self.items == []

    def push(self, item):
        self.items.append(item)

    def pop(self):
        return self.items.pop()

    def peek(self):
        return self.items[len(self.items)-1]

    def 
 
size(self):
        return len(self.items)

def infixToPostfix(infixexpr):
    '''
中綴轉字尾
:param infixexpr:
:return:
    '''
prec = {}
    prec['*'] = 3
prec['/'] = 3
prec['+'] = 2
prec['-'] = 2
prec['('] = 1
opStack = Stack()
    postfixList = []
    # tokenList = infixexpr.split()
    # print(tokenList)
 
for token in infixexpr:
        if token in '0123456789':
            postfixList.append(token)
        elif token == '(':
            opStack.push(token)
        elif token == ')':
            topToken = opStack.pop()
            while topToken != '(':
                postfixList.append(topToken)
                topToken = opStack.pop()
        else
 
:
            while (not opStack.isEmpty()) and \
                    (prec[opStack.peek()] >= prec[token]):
                print(opStack)
                postfixList.append(opStack.pop())
            opStack.push(token)

    while not opStack.isEmpty():
        postfixList.append(opStack.pop())
    return ''.join(postfixList)



def postfixEval(postfixExpr):
    operandStack = Stack()
    # tokenList = postfixExpr.split()
for token in postfixExpr:
        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