def add_done_callback(self, fn):
        """Attaches a callable that will be called when the future finishes.

        Args:
            fn: A callable that will be called with this future as its only
                argument when the future completes or is cancelled. The callable
                will always be called by a thread in the same process in which
                it was added. If the future has already completed or been
                cancelled then the callable will be called immediately. These
                callables are called in the order that they were added.
        """
        with self._condition:
            if self._state is [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED]:
                self._done_callbacks.append(fn)
                return
        fn(self)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/concurrent/concurrent/futures/_base.py/Future.add_done_callback/operator `not in` -> `is`