From the command line enter (in some cases you have to preced the command with sudo):

$ pip install isbnlib


$ easy_install isbnlib


$ pip install isbnlib-3.9.1.tar.gz

(first you have to download the file!)

If you use linux systems, you can install using your distribution package manager (all major distributions have packages python-isbnlib and python3-isbnlib), however (usually) are very old and don’t work well anymore!