Why are CherryPy object attributes persistent between requests?

Question

I was writing debugging methods for my CherryPy application. The code in question was (very) basically equivalent to this:

import cherrypy

class Page:
    def index(self):
        try:
            self.body += 'okay'
        except AttributeError:
            self.body = 'okay'
        return self.body
    index.exposed = True

cherrypy.quickstart(Page(), config='root.conf')

I was surprised to notice that from request to request, the output of self.body grew. When I visited the page from one client, and then from another concurrently-open client, and then refreshed the browsers for both, the output was an ever-increasing string of "okay"s. In my debugging method, I was also recording user-specific information (i.e. session data) and that, too, showed up in both users' output.

I'm assuming that's because the python module is loaded into working memory instead of being re-run for every request.

My question is this: How does that work? How is it that self.debug is preserved from request to request, but cherrypy.session and cherrypy.response aren't?

And is there any way to set an object attribute that will only be used for the current request? I know I can overwrite self.body per every request, but it seems a little ad-hoc. Is there a standard or built-in way of doing it in CherryPy?

(second question moved to How does CherryPy caching work?)

Answer 1

synthesizerpatel's analysis is correct, but if you really want to store some data per request, then store it as an attribute on cherrypy.request, not in the session. The cherrypy.request and .response objects are new for each request, so there's no fear that any of their attributes will persist across requests. That is the canonical way to do it. Just make sure you're not overwriting any of cherrypy's internal attributes! cherrypy.request.body, for example, is already reserved for handing you, say, a POSTed JSON request body.

For all the details of exactly how the scoping works, the best source is the source code.