Şöyle yapabilirsiniz:
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import tkinter as tk
import threading
root = tk.Tk()
entry = tk.Entry(master=root)
entry.grid(row=0, column=0)
def f():
button = tk.Button(master=root, text="Button")
while True:
if entry.get() == "":
button.grid_forget()
else:
button.grid(row=1, column=0)
t1 = threading.Thread(target=f)
t1.daemon = True
t1.start()
t1.join(1)
t2 = threading.Thread(target=root.mainloop)
t2.run()