Hi all, To reproduce this issue, be on cython 0.22 and IPython 3.0 and run the following notebook: http://nbviewer.ipython.org/gist/ngoldbaum/855a629d997aa7959254 Googling the error returns some several year old discussions in IPython related to the autoreload magic and I'm not sure if that is a red herring here: http://mail.scipy.org/pipermail/ipython-dev/2012-May/009288.html For how I'm working around this by calling cython at the command line in my notebook and then loading the annotated HTML with an IFrame. Thanks for your help!