Modal Window

try: #python3 imports
	import tkinter as tk
except ImportError: #python3 failed, try python2 imports
	import Tkinter as tk

class Main(tk.Frame):
	def __init__(self, master=None, **kwargs):
		tk.Frame.__init__(self, master, **kwargs)

		lbl = tk.Label(self, text="this is the main frame")
		lbl.pack()

		btn = tk.Button(self, text='click me', command=self.open_popup)
		btn.pack()

	def open_popup(self):
		print("runs before the popup")
		Popup(self)
		print("runs after the popup closes")

class Popup(tk.Toplevel):
	"""modal window requires a master"""
	def __init__(self, master, **kwargs):
		tk.Toplevel.__init__(self, master, **kwargs)

		lbl = tk.Label(self, text="this is the popup")
		lbl.pack()

		btn = tk.Button(self, text="OK", command=self.destroy)
		btn.pack()

		# The following commands keep the popup on top.
		# Remove these if you want a program with 2 responding windows.
		# These commands must be at the end of __init__
		self.transient(master) # set to be on top of the main window
		self.grab_set() # hijack all commands from the master (clicks on the main window are ignored)
		master.wait_window(self) # pause anything on the main window until this one closes

def main():
	root = tk.Tk()
	window = Main(root)
	window.pack()
	root.mainloop()

if __name__ == '__main__':
	main()