It's an IDLE IDE problem as lilspikey mentioned rather than Python itself. From what I can tell, IDLE listens on a fixed port on localhost in order to communica

It's an IDLE IDE problem as lilspikey mentioned rather than Python itself. From what I can tell, IDLE listens on a fixed port on localhost in order to communicate with the actual Python interpreter, so starting multiple IDLEs may not work. If you run multiple instances of just "python" from the shell (assuming UNIX), there is no problem. GIL is not involved here, it only comes into play when you have multiple threads in a single process. I don't use IDLE, but http://mail.python.org/pipermail/patches/2006-July/020329.html http://mail.python.org/pipermail/patches/2006-July/020329.ht... suggests there's some "-n" switch you can IDLE with that alleviates the problem somehow.