basic-calculator-iii.py

class Solution:
    def calculate(self, s):
        """
        :type s: str
        :rtype: int
        """
        num, stack, sign = 0, [], "+"
        s += " "
        i = 0
        while i < len(s):
            if s[i].isdigit():
                num = num * 10 + int(s[i])
            elif s[i] == "(":
                num, skip = self.calculate(s[i + 1 :])
                i += skip
            elif s[i] in "+-*/)" or i == len(s) - 1:
                if sign == "+":
                    stack.append(num)
                elif sign == "-":
                    stack.append(-num)
                elif sign == "*":
                    stack.append(stack.pop() * num)
                elif sign == "/":
                    stack.append(int(stack.pop() / num))
                if s[i] == ")":
                    return sum(stack), i + 1
                num = 0
                sign = s[i]
            i += 1
        return sum(stack)