When we change the state of the button to DISABLED, the callback continues its execution, so the state of the button is not actually changed until the system is idle, which means it has to wait for time.sleep() to complete.

However, we can force Tkinter to update all the pending GUI updates to execute at a specific moment, as shown in the following script:

import time
import tkinter as tk

class App(tk.Tk):
    def __init__(self):
        super().__init__()
        self.button = tk.Button(self, command=self.start_action,
                                text="Wait 1 second")
        self.button.pack(padx=30, pady=20)

    def start_action(self):
        self.button.config(state=tk.DISABLED)
        self.update_idletasks()
        time.sleep(1)
        self.button.config(state=tk.NORMAL)

if __name__ == "__main__":
    app = App()
    app.mainloop()