If library contains function like

function(*variable_arguments, __helper_functions)

import failed with

[ ERROR ] Adding keyword 'function' to library 'Library' failed: ValueError: Function has keyword-only arguments or annotations, use getfullargspec() API which can support them

Robot Framework 3.0.2
Python 3.5.2
Ubuntu 16.04 / x86_64 / Linux 4.4.0

UPDATE by @pekkaklarck: The above problem that keyword-only arguments prevented using keywords altogether was fixed in RF 3.0.3 by #2627. This issue now covers making it possible to actually use those keyword-only arguments.