Because of how the version is managed (https://github.com/rasbt/watermark/blob/master/setup.py#L12), setup.py will fail if there are any mandatory dependencies that are not installed. This means that it cannot run setup.py to get the install_requires unless all of the install_requires are already installed!

This is discussed as option 6 of https://packaging.python.org/guides/single-sourcing-package-version/.

This doesn't show up in CI because ipython is installed separately before watermark is installed.

See here for an example: https://travis-ci.org/github/rasbt/watermark/jobs/739884501