Basic Calculator II

class Solution:
    def calculate(self, s: str) -> int:

        s = s + "+"
        num = 0
        previous_num = 0
        current_num = 0
        prev_operator = "+"
        result = 0

        for i in range(len(s)):
            if s[i].isnumeric():
                current_num = current_num*10 + int(s[i])
            elif s[i] == " ":
                continue
            # consider cases where "+-*/"
            else:
                if prev_operator == "+":
                    num = num + current_num
                    prev_num = current_num
                elif prev_operator == "-":
                    num = num - current_num
                    prev_num = -current_num
                elif prev_operator == "*":
                    num = num - prev_num + prev_num*current_num
                    prev_num = prev_num*current_num
                else:
                    num = num - prev_num + int(prev_num/current_num)
                    prev_num = int(prev_num/current_num)
                current_num = 0
                prev_operator = s[i]

        return num