I agree with jmj's solution, you would want to send a signal of some sort to Thread B from A when some event occurs in A. A queue is one way to do it, but keep in mind that there are numerous ways to communicate between threads/processes (queue, pipe, exit status, TCP/UDP message, etc.). I believe one of the first couple chapters in O'Reilly's "Programming Python" book discusses most of these methods. Choose the simplest one that meets your needs.
-- http://mail.python.org/mailman/listinfo/python-list
