The sage kernel, by comparison, has always worked

I am having the same issue.

@librarianmage Resolved with $ pip install ipykernel

This closed issue shows how to fix the problem:

This looks like your ipykernel install is probably a bit broken. Try:

Re-installing or updating ipykernel:

pip install --upgrade ipykernel

Re-registering the ipython kernel:

python -m ipykernel install --user

There seem to be quite a few people encountering this - I'm wondering whether when euporie is installed in a virtual environment, the default ipykernel kernelspec means that the kernel gets launched from inside euporie's virtalenv, which fails.

I'll do some testing

I think this is caused by an issue in jupyter_client (although it can be worked-around using the steps above). I've reported it upstream.

This closed issue shows how to fix the problem:

This looks like your ipykernel install is probably a bit broken. Try:
Re-installing or updating ipykernel:

pip install --upgrade ipykernel

Re-registering the ipython kernel:

python -m ipykernel install --user

I had this problem and these steps fixed it.

I think they should be put in the install instructions in the README until the issue is fixed.

I think they should be put in the install instructions in the README until the issue is fixed.

This is a good idea - I'll add something