You can do this for testing purposes, but once the proc works you should move it out of the page. Once defined, the proc probably will remain in the thread's interp, so as long as that interp remains alive, the proc you define in one page will be there if the same thread processes a different request. So it would be bad if this proc was overwriting a proc that was defined at startup, if the proc was used on more than the one page you redefine it on.