as another step to python3
Depends on #25373
CC: @bbarros50 @bhutz @sagetrac-atowsley @kcrisman @embray @jdemeyer @jm58660
Component: notebook
Author: Frédéric Chapoton, Jeroen Demeyer
Branch/Commit: 4de168d
Reviewer: Frédéric Chapoton, Jeroen Demeyer
Issue created by migration from https://trac.sagemath.org/ticket/24994