def add_idle(self, callback, *args, **kwds):
self.idlers.append((callback, args, kwds))<EOL>
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.