How to avoid TclError if I want to update the results obtained from entries instantly?

Question

I want to add two numbers and add them and update the result instantly without using a button. I have written this code using after() to do that. from tkinter import *

root = Tk()
root.geometry("400x400")

label1 = Label(root, text="1st number:")
label1.grid(row=0, column=0)

label2 = Label(root, text="2nd number:")
label2.grid(row=1, column=0)

first_no = IntVar()
second_no = IntVar()

entry1 = Entry(root, textvariable=first_no)
entry1.grid(row=0, column=1)

entry2 = Entry(root, textvariable=second_no)
entry2.grid(row=1, column=1)


def auto():
    try:
        S = first_no.get() + second_no.get()
        label3.config(text="Sum:  " + str(S))
        # call again after 100 ms
        root.after(100, auto)
    except TclError:
        print("there is an Error")

label3 = Label(root)
label3.grid(row=3, column=1)

auto()

root.mainloop()

The code works well. However, if we delete the numbers in the entries using the delete or backspace keyboards this error raises: _tkinter.TclError: expected floating-point number but got "", and if I enter new values the code does not work anymore. I wondered to know how I avoid this problem??

Answer 1

I found the solution. I added another root.after(100, auto) under exception TclError