python, what would i put in class mainwindow to display clock? import tkinter as tk import time class Clock(): def __init__(self): self.label = tk.Label(text="", font=('Helvetica', 48), fg='red') self.label.pack() self.update_clock() def update_clock(self): now = time.strftime("%H:%M:%S") self.label.configure(text=now) self.root.after(1000, self.update_clock) class mainwindow(): def __init__(self): self.root = tk.Tk() self.root.mainloop() app = mainwindow()