from __future__ import print_function

#
# Create a GUI with a single button that causes
# the event loop to terminate.
#
try:
    import Tkinter
except ImportError:
    import tkinter as Tkinter

# Once again, our main application frame
app = Tkinter.Frame()
app.grid()

# This is the callback that will be invoked when the
# button is pushed.
def quit_cb(app=app):
    app.quit()

# This time, we add a "command" argument whose value
# is the function to call when the button is pressed.
# Note that we never call "quit_cb" directly from our
# code; we depend on Tkinter to call it at the
# appropriate time.
button = Tkinter.Button(app, text="Quit", command=quit_cb)
button.grid(row=0, column=0)
# Again, enter the event loop and wait for it to end.
app.mainloop()
print("Finished")