[Twisted-web] Implement "Page Not Found "

[Tsai Li Ming]

Dear All

How do I implement a 404 Page Not Found using twisted web for those 
resources that I did not add using putChild?

class Server(resource.Resource):
     def getChild(self, name, request):
         if name == '':
             return self
         return Resource.getChild(self, name, request)

Thanks,
-Liming