future.py 文件源码

def set_exception(self, exception):
        " Mark the future done and set an exception. "
        if self._done:
            raise InvalidStateError('Future result has been set already.')

        self._exception = exception
        self._done = True

        if self.done_callbacks:
            self._call_callbacks()
        else:
            # When an exception is set on a 'Future' object, but there
            # is no callback set to handle it, print the exception.
            # -- Uncomment for debugging. --

            # import traceback, sys
            # print(''.join(traceback.format_stack()), file=sys.__stderr__)
            # print('Uncollected error: %r' % (exception, ), file=sys.__stderr__)
            pass