I don't see any obvious spots where the program might go into an infinite loop and without more information it is hard to tell where to start.

A general strategy for debugging these sorts of problems is to put print statements in the code saying "I got here" and then run it to see if you got there. If you got there, check later in the program, if not, check earlier. This will allow you to soon find the pathological code.

To help us solve your problem, you might also describe how the code hangs. Is any output produced? Did you try -w to catch typos?

-Mark