Мне нужно чтобы в модуле tkinter, при вводе в калькуляторе буквы и другие символы не вводились кроме цифр и знаков действий

import tkinter as tk
from tkinter import messagebox

def add_digit(digit):
    value = calc.get()
    if value[0] == '0' and len(value) == 1:
        value = value[1:]
    calc.delete(0, tk.END)
    calc.insert(0, value + digit)


def add_operation(operation):
    value = calc.get()
    if value[-1] in '-+/*':
        value = value[:-1]
    calc.delete(0, tk.END)
    calc.insert(0, value + operation)


def calculate():
    value = calc.get()
    if value[-1] in '+-*/':
        value = value + value[:-1]
    elif '+' in value or '-' in value or '*' in value or '/' in value:
        value = calc.get()
    calc.delete(0, tk.END)
    try:
        calc.insert(0, eval(value))
    except (NameError,SyntaxError):
        messagebox.showinfo('внимание','Нужно вводить другие цифры' ,'Вы ввели другие символы')
        calc.insert(0,0)
    except ZeroDivisionError:
        messagebox.showinfo('внимание','на ноль делить нельзя')
        calc.insert(0, 0)



def clear():
    calc.delete(0, tk.END)
    calc.insert(0, 0)

def press_key(event):
    print(repr(event.char))
    if event.char.isdigit():
        add_digit(event.char)
    elif event.char in '+-/*':
        add_operation(event.char)
    elif event.char == '\r':
        calculate()
def make_digit_button(digit):
    return tk.Button(text=digit, bd=5, font=('Arial', 13), command=lambda: add_digit(digit))


def make_operation_button(operation):
    return tk.Button(text=operation, bd=5, font=('Arial', 13), fg='red', command=lambda: add_operation(operation))


def make_calc_button(operation):
    return tk.Button(text=operation, bd=5, font=('Arial', 13), fg='red', command=calculate)


def make_clear_button(operation):
    return tk.Button(text=operation, bd=5, font=('Arial', 13), fg='red', command=clear)





root = tk.Tk()
root.title('калькулятор')
root['bg'] = '#33ffe6'
root.geometry(f"350x300+100+200")
root.bind('<Key>', press_key)
calc = tk.Entry(root, justify=tk.RIGHT, font=('Arial', 15), width=15)
calc.insert(0, '0')
calc.grid(row=0, column=0, columnspan=4, stick='we', padx=5)
make_digit_button('1').grid(row=1, column=0, stick='wens', padx=5, pady=5)
make_digit_button('2').grid(row=1, column=1, stick='wens', padx=5, pady=5)
make_digit_button('3').grid(row=1, column=2, stick='wens', padx=5, pady=5)
make_digit_button('4').grid(row=2, column=0, stick='wens', padx=5, pady=5)
make_digit_button('5').grid(row=2, column=1, stick='wens', padx=5, pady=5)
make_digit_button('6').grid(row=2, column=2, stick='wens', padx=5, pady=5)
make_digit_button('7').grid(row=3, column=0, stick='wens', padx=5, pady=5)
make_digit_button('8').grid(row=3, column=1, stick='wens', padx=5, pady=5)
make_digit_button('9').grid(row=3, column=2, stick='wens', padx=5, pady=5)
make_digit_button('0').grid(row=4, column=0, stick='wens', padx=5, pady=5)
make_operation_button('+').grid(row=1, column=3, stick='wens', padx=5, pady=5)
make_operation_button('-').grid(row=2, column=3, stick='wens', padx=5, pady=5)
make_operation_button('/').grid(row=3, column=3, stick='wens', padx=5, pady=5)
make_operation_button('*').grid(row=4, column=3, stick='wens', padx=5, pady=5)
make_calc_button('=').grid(row=4, column=2, stick='wens', padx=5, pady=5)
make_clear_button('C').grid(row=4, column=1, stick='wens', padx=5, pady=5)
root.grid_columnconfigure(0, minsize=70)
root.grid_columnconfigure(1, minsize=70)
root.grid_columnconfigure(2, minsize=70)
root.grid_columnconfigure(3, minsize=70)
root.grid_rowconfigure(1, minsize=60)
root.grid_rowconfigure(2, minsize=60)
root.grid_rowconfigure(3, minsize=60)
root.grid_rowconfigure(4, minsize=60)

root.mainloop()

И если можно, пожалуйста код с объяснением