I have an app that is centered around IPython running in qt (https://github.com/neuropy/neuropy/blob/master/neuropy/main.py). Yesterday I updated IPython from git, and have had to change a few things since the refactoring about 3 months ago, which split a kernel client off of the kernel manager (see #3011). In the process, I came across the error in the title. This error only happens when I try to create a normal two-process app, but not when creating an inprocess app, ie, it happens with QtKernelManager, but not with QtInProcessKernelManager. I think a BlockingKernelClient happens to be the default for QtKernelClient, which may be due to #3222. Not sure how to fix this in IPython, but to get around it, I set the client_factory to QtKernelClient, and then calling QtKernelManager.client() works fine. My minimalist example is in this gist: https://gist.github.com/mspacek/6018206

Can this be fixed so that setting up the 2-process app doesn't require the extra step of changing the client_factory?