I’m inclined to reject the bug: http://docs.python.org/distutils/apiref#distutils.core.setup clearly says that the argument should be a dictionary.  The code in pyreadline should set it to an empty dict instead of None.  While it can be argued that providing clearly helpful messages is a service for our users, especially given that people writing setup scripts may be beginners, it seems to me that adding type checking would not be the Python way.  Raymond, what do you think?