Я делаю калькулятор на Python, и он показывает ошибку при вычислении выражений со скобками

Он показывает эту ошибку при вычислении выражений со скобками типа-> 86 * 4 (3 + 5) 88:

TypeError: объект int не вызывается

когда я не использую кнопки калькулятора и не набираю текст с помощью кнопок на клавиатуре, он не показывает никаких ошибок, но при нажатии равно дает неправильный ответ.

Пожалуйста, проверьте мой код и укажите на ошибку.

from tkinter import *

cal = Tk()
cal.title("Smart Calculator")

txtDisplay = Entry(cal, font=('arial', 20, 'bold'), bd=30, insertwidth=4, 
bg = "powder blue", justify='right')

class Calculator:

    def __init__(self):
        self.result = 0
        self.current = 0
        self.operator = ""

    def btnClick(self, num):
            self.operator = self.operator + str(num)
            txtDisplay.delete(0, END)
            txtDisplay.insert(0, self.operator)
            self.expOutput(self.operator)

    def expOutput(self, operator):
        try:
            self.result = str(eval(operator))
            txtDisplay.delete(0, END)
            txtDisplay.insert(0, string=self.operator + " = " + self.result)
            self.current = 0
        except SyntaxError:
            txtDisplay.delete(0, END)
            txtDisplay.insert(0, self.operator)

    def oprtrClick(self, op):
        if self.current is 0:
            self.current = 1
            self.operator = self.operator + op
            txtDisplay.delete(0, END)
            txtDisplay.insert(0, string=self.operator)
        else:
            self.operator = self.operator + op
            self.expOutput(self.operator)

    def equals(self):
        self.operator = self.result
        txtDisplay.delete(0, END)
        txtDisplay.insert(0, string=self.operator)

    def clear(self):
        self.__init__()
        txtDisplay.delete(0, END)

    def delete(self):
        self.operator = self.operator[: -1]
        txtDisplay.delete(0, END)
        txtDisplay.insert(0, string=self.operator)

smartCal = Calculator()

btn0 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 
'bold'), text = "0",bg = "powder blue", command=lambda: smartCal.btnClick(0))


btn1 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 
'bold'), text = "1",
          bg = "powder blue", command=lambda: smartCal.btnClick(1))

btn2 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 
'bold'), text = "2",bg = "powder blue", command=lambda: smartCal.btnClick(2))


btn3 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 
'bold'), text = "3",
          bg = "powder blue", command=lambda: smartCal.btnClick(3))

btn4 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "4",
          bg = "powder blue", command=lambda: smartCal.btnClick(4))

btn5 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "5",
          bg = "powder blue", command=lambda: smartCal.btnClick(5))

btn6 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "6",
          bg = "powder blue", command=lambda: smartCal.btnClick(6))

btn7 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "7",
          bg = "powder blue", command=lambda: smartCal.btnClick(7))

btn8 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "8",
          bg = "powder blue", command=lambda: smartCal.btnClick(8))

btn9 = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "9",
          bg = "powder blue", command=lambda: smartCal.btnClick(9))

btnDecimal = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = ".",
               bg = "powder blue", command=lambda: smartCal.btnClick("."))

btnLeftParen = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "(",
               bg = "powder blue", command=lambda: smartCal.btnClick("("))

btnRightParen = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = ")",
               bg = "powder blue", command=lambda: smartCal.btnClick(")"))

Add_btn = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "+",
             bg = "powder blue", command=lambda: smartCal.oprtrClick("+"))

Sub_btn = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "-",
             bg = "powder blue", command=lambda: smartCal.oprtrClick("-"))

Mul_btn = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "*",
             bg = "powder blue", command=lambda: smartCal.oprtrClick("*"))

Div_btn = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "/",
             bg = "powder blue", command=lambda: smartCal.oprtrClick("/"))

btnEquals = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = " = ",
               bg = "powder blue", command=smartCal.equals)

btnClear = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "C",
              bg = "powder blue", command=smartCal.clear)

btnBackspace = Button(cal, padx=16, pady=16, bd=8, fg = "black", font=('arial', 20, 'bold'), text = "⌫",
              bg = "powder blue", command=smartCal.delete)

# ~*~*~Positioning~*~*~

txtDisplay.grid(columnspan=4)
# =========ROW1================== #
btn7.grid(row=1, column=0)
btn8.grid(row=1, column=1)
btn9.grid(row=1, column=2)
Add_btn.grid(row=1, column=3)
# =========ROW2================== #
btn4.grid(row=2, column=0)
btn5.grid(row=2, column=1)
btn6.grid(row=2, column=2)
Sub_btn.grid(row=2, column=3)
# =========ROW3================== #
btn1.grid(row=3, column=0)
btn2.grid(row=3, column=1)
btn3.grid(row=3, column=2)
Mul_btn.grid(row=3, column=3)
# =========ROW4================== #
btn0.grid(row=4, column=0)
btnClear.grid(row=4, column=1)
btnEquals.grid(row=4, column=2)
Div_btn.grid(row=4, column=3)
# =========ROW5================== #
btnDecimal.grid(row=5, column=0)
btnLeftParen.grid(row=5, column=1)
btnRightParen.grid(row=5, column=2)
btnBackspace.grid(row=5, column=3)

cal.mainloop()