def recv(self, timeout=None):
        """Receive an ISOTP frame, blocking if none is available in the buffer
        for at most 'timeout' seconds."""

        try:
            return self.rx_queue.get(timeout is None or timeout > 0, timeout)
        except queue.Empty:
            return None
Receive an ISOTP frame, blocking if none is available in the buffer
        for at most 'timeout' seconds.