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Your banner tells us that you are running a Python 3-based Sage. sagenb (the classical notebook) is NOT compatible/supportable with Python 3. This incompatibility has been known and published for a long time, and this classicalnotebook has been deprecated for a while...
If you want to use a Python 3-based Sage, you have to use the Jupyter notebook (or another interface, such sage-shell-mode for emacs, or the JupyterLab notebook (optional package)).
If you insist on the classical Sage notebook, you have to install a Python 2-based Sage. As far as I can tell, in has been announced that 9.1 would be the last Sage version to support Python 2. Furthermore, I do not know if precompiled Python 2-based package(s) exist(s) for which distribution(s). Last but not least, choosing to stay with Python 2-based Sage entails staying with (at best) Sage 9.1. Since Sage 9.2, the Python 2-specific code is being pruned from Sage source...
BTW : in 9.3.beta2, notebook() no longer exists...
HTH,
