iostream.py 文件源码

def _set_read_callback(self, callback):
        assert self._read_callback is None, "Already reading"
        assert self._read_future is None, "Already reading"
        if callback is not None:
            self._read_callback = stack_context.wrap(callback)
        else:
            self._read_future = TracebackFuture()
        return self._read_future