RIP (for now) Calibre in Debian
The current purge of all Python2 related packages has a direct impact on Calibre. The latest version of Calibre requires Python modules that are not (anymore) available for Python 2, which means
that Calibre >= 4.0 will for the foreseeable future not be available in Debian Update 20191028: Calibre 4.2 based on Python2 is in Debian/unstable.
I just have uploaded a version of 3.48 which is the last version that can run on Debian. From now on until upstream Calibre switches to Python 3, this will be the last version of Calibre in Debian.
In case you need newer features (including the occasional security fixes), I recommend switching to the upstream installer which is rather clean (installing into
/opt/calibre, creating some links to the startup programs, and installing completions for zsh and bash. It also prepares an uninstaller that reverts these changes.