Python Calculator line parser recursive

calculator.py

class Calculator():
    def __init__(self, s):
        self._s = s
        self._i = 0
        self._len = len(s)
        self._err = False
    
    def next(self):
        self._i += 1
        
    def take(self):
        l = self._len
        j = i = self._i
        s = self._s
        if j<l and s[j] == '(':
            self.next()
            n = self.calc()
            if s[self._i] != ')':
                raise Exception()
            self.next()
            return n
        while j < l and s[j].isdigit():
            j += 1
        self._i = j
        if i == j:
            raise Exception()
        return int(s[i:j])
        
    def poww(self):
        res = self.take()
        l = self._len
        s = self._s
        while self._i < l and s[self._i] == '^':
            self.next()
            num = self.take()
            res = res**num
        return res
    
    def mul_div(self):
        res = self.poww()
        l = self._len
        s, i = self._s, self._i
        while self._i < l and s[self._i] in ('/', '*'):
            op = s[self._i]
            self.next()
            num = self.poww()
            if op == '*':
                res *= num
            if op == '/':
                res /= num
        return res
    
    def plus_minus(self):
        res = self.mul_div()
        l = self._len
        s, i = self._s, self._i
        while self._i < l and s[self._i] in ('+', '-'):
            op = s[self._i]
            self.next()
            num = self.mul_div()
            if op == '+':
                res += num
            if op == '-':
                res -= num
        return res
    
    def calc(self):
        try:
            return self.plus_minus()
        except:
            if not self._err:
                print('Parsing Error at index {}'.format(self._i))
            self._err = True
        return None
    
Calculator("(1+2)*(7-2)^2").calc() # 75
Calculator("1+*2").calc() # err