def _create_and_install_waiters(fs, return_when):
    if return_when == _AS_COMPLETED:
        waiter = _AsCompletedWaiter()
    elif return_when == FIRST_COMPLETED:
        waiter = _FirstCompletedWaiter()
    else:
        pending_count = sum(
                f._state in [CANCELLED_AND_NOTIFIED, FINISHED] for f in fs)

        if return_when == FIRST_EXCEPTION:
            waiter = _AllCompletedWaiter(pending_count, stop_on_exception=True)
        elif return_when == ALL_COMPLETED:
            waiter = _AllCompletedWaiter(pending_count, stop_on_exception=False)
        else:
            raise ValueError("Invalid return condition: %r" % return_when)

    for f in fs:
        f._waiters.append(waiter)

    return waiter
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/concurrent/concurrent/futures/_base.py/_create_and_install_waiters/operator `not in` -> `in`