How do you terminate/break/abort a Python console/sys.stdin readline()?

In thread, I have a loop that reads input from the user console. The main thread is busy with a Tkinter mainloop(). How do I terminate this program?

while True:
    ln = sys.stdin.readline()
    try:
        ln = ln[:-1]  # Remove LF from line
        if len(ln)==0: continue  # Ignore blank lines
        ...and so on

The main thead calls startGUI() which contains a tk.mainloop() call. When I press the X close button on the window (this is Linux), Tkinter closes the window and mainloop() returns. I then try to close stdin hoping that sys.stdin will close and cause sys.stdin.readline() will terminate with a nice EOF allowing my stdinLoop thread terminate.

# Start up the GUI window
startGUI()  # Doesn't return until GUI window is closed, tk.mainloop is called here
#
# Wait for stdinLoop thread to finish
sys.stdin.close()  # Hopefully cause stdinTh to close
print("waiting for stdinTh to join")
stdinTh.join()
print("joined stdinTh")

The sys.stdin.realine() never returns after the sys.stdin.close(). (The stdinTh.join() was there to synchronize the closing.)

I think Python readline() is doing something clever (in something called NetCommand) that doesn't return cleanly when stdin is closed.

Does Python think it is evil to have both a Tkinter GUI and use stdin interactively?

I tried using sys.stdin.read(1), but is seems buffer up a line and returns the whole line -- rather than reading one byte/char as I thought a read(1) would.