def error_future(self):
        """
        Return a future which will receive the next XML stream error as
        exception.

        It is safe to cancel the future at any time.
        """
        fut = asyncio.Future(loop=self._loop)
        self._error_futures.append(fut)
        return fut
Return a future which will receive the next XML stream error as
        exception.

        It is safe to cancel the future at any time.