[mod_python] How to terminate responce?

Hi,

With PSP, how to terminate current response?

I want to check some condition, if it's satisfied, I'll continue, 
otherwise I'll finish current page. To finish current page, is there
some function like "req.end()"?

For example, the PSP script is as follows:

<%
if xx != 0:
   req.end(); 

...
%>

Actually, there isn't a function "req.end()". I've try to use
"sys.exit()" instead, but this one will cause a exception. 
I want to finish the page normally, not a exception.
Can you give me some hints?

Clark