import tkinter as tk
import datetime
import time

class Application(tk.Frame):
    def __init__(self, master=None):
        super().__init__(master)
        self.master = master
        self.pack()
        self.seconds_left = 0
        self._timer_on = False
        self.create_widgets()

    def create_widgets(self):
        self.button = tk.Button(self, text="開始", fg="red",command=self.start)
        self.button.pack()

    def start(self):
        self.pop = tk.Toplevel()
        self.label = tk.Label(self.pop, text="00:00:00")
        self.label.pack()
        self.start_button()

    def countdown(self):
        self.label['text'] = self.convert_seconds_left_to_time()
        if self.seconds_left:
            self.seconds_left -= 1
            self._timer_on = self.after(1000, self.countdown)
        else:
            self._timer_on = False

    def start_button(self):
        self.seconds_left = 90
        self.stop_timer()                           
        self.countdown()                            
        
        a = 0
        
        while a <100:
            a = a + 1
            time.sleep(0.1)
            
    def stop_timer(self):
        if self._timer_on:
            self.after_cancel(self._timer_on)
            self._timer_on = False

    def convert_seconds_left_to_time(self):
        return datetime.timedelta(seconds=self.seconds_left)


root = tk.Tk()
app = Application(master=root)
app.mainloop()

小弟想請教的是
我toplevel明明放在前面
為什麼它會執行while的東西後 才跳出視窗倒數呢
而且整個程式會當掉 變成沒有回應