StackStack

class :
    
    def __init__(self):
        self.stack = []

    def SisEmpty(self):
        return len(self.stack) == 0

    def SPush(self, val):
        self.stack.append(val)

    def SPop(self):
        if self.SisEmpty():
            return None
        else:
            return self.stack.pop()

    def SPeek(self):
        index = len(self.stack) - 1
        if self.SisEmpty():
            return None
        else:
            return self.stack[index]


## Result

if __name__ == '__main__':
    s_stack = Stack()
    s_stack.SPush(10)
    s_stack.SPush(20)
    s_stack.SPush(30)
    s_stack.SPush(40)

    print(s_stack.SisEmpty())   #false
    print(s_stack.SPeek())  #40
    print(s_stack.SPop())   #40
    print(s_stack.SPop())   #30
    print(s_stack.SPeek())  #20

convertToPostfix
# 입력받은 연산자를 후위연산자로 변환한다.

getOpPrec
#연산자의 가중치를 리턴한다.

get_postfix_exp
#후위연산자를 리턴한다.

from stack import Stack

class PostfixCalculate:
    # 원래 주어진 수식
    # origin_exp
    # 결과 (후위 수식)
    # postfix_exp

    # method
    def __init__(self, origin):
        self.origin_exp = origin
        self.postfix_exp = None

    def getOpPrec(self,op):
        if op == '*' or op == '/':
            return 5
        elif op == '+' or op == '-':
            return 3
        elif op == '(':
            return 1
        else:
            return -1   # 등록되지 않은 수식


    def convertToPostfix(self):
        exp_list = []
        operate_stack = Stack()

        #숫자와 수식을 구별한다
        for i in self.origin_exp:

            if i.isdigit():
                exp_list.append(i)
            else:
                # ( 거나 스택이 비었을 경우
                if i == '(' or operate_stack.SisEmpty():
                    operate_stack.SPush(i)
                # ) 경우 연산자를 모두 배열에 넣기
                elif i == ')':
                    operation = operate_stack.SPop()
                    exp_list.append(operation)
                # 기존의 연산자보다 비중이 높다면 그대로 유지
                elif self.getOpPrec(i) > self.getOpPrec(operate_stack.SPeek()):
                    operate_stack.SPush(i)
                # 기존의 연산자보다 비중이 같거나 낮을때
                else:

                    while not operate_stack.SisEmpty() and self.getOpPrec(i) <= self.getOpPrec(operate_stack.SPeek()):
                       operation = operate_stack.SPop()
                       exp_list.append(operation)
                    operate_stack.SPush(i)

        while not operate_stack.SisEmpty():
            op = operate_stack.SPop()
            exp_list.append(op) 
        self.postfix_exp = ''.join(exp_list)

    def get_postfix_exp(self):
        if not self.postfix_exp:
            self.convertToPostfix()

        return self.postfix_exp


if __name__ == '__main__':
    origin = input("수식을 입력해주세요: ")

    calcurate = PostfixCalculate(origin)
    calcurate.convertToPostfix()
    print("resutl:", calcurate.get_postfix_exp())