Currently, the dependency on pyyaml is a bit schyzophrenic:

• it's in requirements.txt, which doesn't really explain what's what and is not used for normal installations
• it's in the setup_requires of setup.py, which is for build-time dependencies

This means it will not work by default, the install will work then the import will fail when trying to load the yaml file.

Packaging thingies apparently have support for optional extras which can be opted in: https://setuptools.pypa.io/en/latest/userguide/dependency_management.html#optional-dependencies