> The first time A starts, it should open a B process and start > communicating with it. All other times an A instance starts it should > simply talk with the B that already is open.
B should write its process id to a location known by both applications. When A starts, it should read that PID from the file and attempt to communicate with the process having that PID. When B starts, it should also check for the file. If it's found and if the PID in it is present in the process table, then B should exit. Otherwise, it should start normally and write its own PID to the file. -- http://mail.python.org/mailman/listinfo/python-list
