'Add an idle callback.
An idle callback can return True, False or None.  These mean:
- None: remove the callback (don\'t reschedule)
- False: the callback did no work; reschedule later
- True: the callback did some work; reschedule soon
If the callback raises an exception, the traceback is logged and
the callback is removed.'

def add_idle(self, callback, *args, **kwds):

    self.idlers.append((callback, args, kwds))
