I am developing a Python 2.7.1 / Tkinter 8.4 app on Windows XP that checks several lines of input from a RS-232 port. However, if no input arrives it will sit in a loop for ever. 
I am trying to implement an ‘Abandon Test’ button on the GUI but because the main thread  is busy waiting for input it doesn’t appear to every check if a button has been pressed.
I have tried update_idletasks() and time.sleep(1) with no success. 
Any suggestions?
Tk is single-threaded, so if the main thread is busy the GUI will freeze. One solution is to use a separate thread to do the reading, so when the read blocks your main thread can continue. When you get a line of input you can push it on a queue which is monitored by the main thread. 
The other way is to figure out how to do a non-blocking read on your serial port. If there is data, read it. If not, return to the main event loop. You then need to configure the event loop to poll your port every few hundred milliseconds or so, depending on your performance needs.
How can I monitor Tkinter buttons when Python is busy?