MarsSeed [1] filed a deletion request for python2-isbnlib-git [2]: Unneeded Python2 VCS package from 2015.
Development happens on the 'dev' branch, not on 'master'. But upstream supports Python3; AUR has both a stable and a VCS package for that. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/python2-isbnlib-git/
