I have installed xidlehook in arch linux via AUR and it seems as though the comment here:
https://github.com/quantopian/PenguinDome/blob/master/client/plugins/screenlock.py#L125
reflects a perhaps-out-of-date version of xidlehook.

My usage of xidlehook only uses a duration, command and canceller:
--timer <duration> <command> <canceller>