Text in tkinter

Question

I want that when the "Start" button is pressed, it executes code and counts from 3 (3... 2... 1... Ready!), with delay between each and printing the numbers in the program window. I used tkinter. But I can't get the countdown to appear when I press the "Start" button. And I don't know how to add the code that is executed after pressing the button.

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import tkinter as tk
from tkinter import ttk
import time
class Aplicacion:
    def __init__(self,master):
        self.master=master
        self.master.title('Title')
        self.master.geometry('290x50')
        self.inicializar_gui()
    def inicializar_gui(self):
        lbl_bienvenido=tk.Label(self.master,text='Hi!',font=('Helvetica',10))
        lbl_bienvenido.place(x=0,y=0)
        btn_login=tk.Button(self.master,text='Start')
        btn_login['command']=self.comando
        btn_login.place(x=10,y=23)
    def comando(self):
        entry = ttk.Entry(state=tk.DISABLED, takefocus=False)
        entry.place(x=63, y=25)
        entry.insert(0, "1...")
        # print("3")
        # time.sleep(1)
        # print("2")
        # time.sleep(1)
        # print("1")
        # time.sleep(1)
        # print("Ready!")
def main ():
    root = tk.Tk()
    ventana = Aplicacion(root)
    root.mainloop()

if __name__ == "__main__":
    main()

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