Can not create a new Label in Tkinter

In this program, I have simulated a failure in a connection. At first, a "Connecting..." label is displayed. After the failure, the label will change to "Connection Failed." and a try again button is displayed. When the try again button is pressed, I want to destroy the "Connection Failed." label and create a new "Connecting..." label. The destruction happens successfully but a new "Connecting..." label can not be created and I can not see that. I also tried to modify the "Connection Failed." text to "Connecting..." using the config method but it does not work either. It is weird...

import time
import tkinter as tk
import signal

signal.signal(signal.SIGINT, signal.SIG_DFL)
# Create main window
root = tk.Tk()

screen_width = root.winfo_screenwidth()
screen_height = root.winfo_screenheight()
root.geometry(f"{screen_width}x{screen_height}")
is_connection_done = tk.StringVar(value="")
try_again_button = None
connecting_message = None

def connect():
    global try_again_button, connecting_message, root
    print('Trying to connect')
    if try_again_button:
        try_again_button.destroy()
        try_again_button = None
        connecting_message.destroy()
        connecting_message = tk.Label(root, text="Connecting...")
        connecting_message.pack()
        

    time.sleep(2)
    is_connection_done.set("failed")
    
connecting_message = tk.Label(root, text="Connecting...")
connecting_message.pack()
connection_event_id = root.after(1000, connect)

while True:
    is_connection_done.set("")
    root.wait_variable(is_connection_done)
    if is_connection_done.get() == 'done':
        connecting_message.config(text='Connected Successfully!')
        break
    elif is_connection_done.get() == 'failed':
        print('Failed')
        connecting_message.config(text='Connection Failed.')
        try_again_button = tk.Button(root, text='Try Again', command=connect)
        try_again_button.pack()
        
        
# Start event loop
root.mainloop()

Since the while loop blocks root.mainloop() from executing, so tkinter mainloop cannot take control and update widgets.

You can call connecting_message.update() after connecting_message.pack() inside connect() to force the update.

However, it is not recommended to use while loop in a tkinter application. Use after() instead.

import time
import tkinter as tk
import signal

signal.signal(signal.SIGINT, signal.SIG_DFL)
# Create main window
root = tk.Tk()

screen_width = root.winfo_screenwidth()
screen_height = root.winfo_screenheight()
root.geometry(f"{screen_width}x{screen_height}")
is_connection_done = tk.StringVar(value="")

def connect():
    # hide the "Try Again" button
    try_again_button.pack_forget()
    # update label text
    connecting_message.config(text="Connecting...")
    # use after() instead of time.sleep(2)
    root.after(2000, is_connection_done.set, "failed")

connecting_message = tk.Label(root, text="Connecting...")
connecting_message.pack()
connection_event_id = root.after(1000, connect)

# create the button but initially hidden
try_again_button = tk.Button(root, text='Try Again', command=connect)

def checking():
    is_connection_done.set("")
    root.wait_variable(is_connection_done)
    if is_connection_done.get() == 'done':
        connecting_message.config(text='Connected Successfully!')
        return   # stop the checking loop
    elif is_connection_done.get() == 'failed':
        connecting_message.config(text='Connection Failed.')
        # show the "Try Again" button
        try_again_button.pack()
        root.after(100, checking) # schedule next checking

# start checking loop
checking()
# Start event loop
root.mainloop()