题解 | #四则运算#

n = input()
nums = '0123456789'
operators = '+-*/[](){}'
numstack =[] #记录数字
operatorstack = [] #纪录操作符并判断优先级

def szys(a,b,s):
    if s == '+':
        return a+b
    elif s == '-':
        return a-b
    elif s == '*':
        return a*b
    else:
        return int(a/b)
prev = ''
flag = 1
for s in n :
    if s in nums:
        if prev in operators or not prev:
            numstack.append(flag*int(s))
        else:
            numstack.append(10*numstack.pop()+flag*int(s))
    else:
        flag = 1
        if s in '+-':
            if not numstack:
                numstack.append(0)
            if not operatorstack:
                operatorstack.append(s)
            else:
                if prev in '([{' :
                    if s =="+":
                        flag = 1
                    else:
                        flag = -1
                    continue
                while operatorstack and operatorstack[-1] in '+-*/':
                    tempoperator = operatorstack.pop()
                    numb = numstack.pop()
                    numa = numstack.pop()
                    numstack.append(szys(numa,numb,tempoperator))
                operatorstack.append(s)             
        elif s in '*/':
            operatorstack.append(s)
        elif s in '([{':
            operatorstack.append('(')  
        else:
            while operatorstack[-1] != '(':
                tempoperator = operatorstack.pop()
                numb = numstack.pop()
                numa = numstack.pop()
                numstack.append(szys(numa,numb,tempoperator))
            operatorstack.pop()
    prev = s

while operatorstack:
    tempoperator = operatorstack.pop()
    numb = numstack.pop()
    numa = numstack.pop()
    numstack.append(szys(numa,numb,tempoperator))

print(numstack[0])

不用eval的做法，改了俩小时才对，写进题解里自己记录一下