I can get a similar error from time to time, just try it a couple of times and I believe you should hit it too. When that error isn't thrown IDLE prints the traceback of a SystemExit exception inside IDLE right before closing, so it may be hard to notice. The error I am able to get (using 3.1rc2+ r73431): *** Internal Error: rpc.py:SocketIO.localcall() Object: stderr Method: <bound method PseudoFile.write of <idlelib.PyShell.PseudoFile object at 0x8b6084c>> Args: ('SystemExit: None\n',) Traceback (most recent call last): File "/home/gpolo/python-dev/py3k/Lib/idlelib/rpc.py", line 188, in localcall ret = method(*args, **kwargs) File "/home/gpolo/python-dev/py3k/Lib/idlelib/PyShell.py", line 1231, in write self.shell.write(s, self.tags) File "/home/gpolo/python-dev/py3k/Lib/idlelib/PyShell.py", line 1214, in write self.text.mark_gravity("iomark", "left") AttributeError: 'NoneType' object has no attribute 'mark_gravity' I'm not sure if it can't happen in python-trunk too, I see it throws an exception when leaving IDLE but till now I never got an error message after IDLE (almost) exited.