async def wait_changed(self):
if not self.is_complete():<EOL><INDENT>waiter = self._loop.create_future()<EOL>self._waiters.append(waiter)<EOL>await waiter<EOL><DEDENT>
Waits until the result set changes. Possible changes can be a result
being added or the result set becoming complete. If the result set is
already completed, this method returns immediately.