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You want to add the same GET/POST parameter to each controller method, but using **kwargs on every controller method is cumbersome. Imagine you want to be able to change the “skin” variable on any controller.
Using CherryPy filters you can intercept the request before it reaches the controller method and add/remove parameters from the request object. You could then, for example, put this request into the session.
So the way to go about this is:
Write a CherryPy filter.
Append the filter to a controller.
Important
Note that the filter will be also active for all sub-controllers inside that controller!
from cherrypy.filters.basefilter import BaseFilter from cherrypy import request, session class SkinFilter(BaseFilter): """If the request parameters contain a "skin" variable, pull it out of the request and put it into the session. """ __detected_skin = None def before_request_body(self): try: if "skin" in request.params: skin = request.params.pop("skin") if skin is not None: self.__detected_skin = skin except Exception, exc: log.warning("Error in %s:\n%s", self.__class__.__name__, exc) def before_main(self): if self.__detected_skin is not None: session['skin'] = self.__detected_skin
Top activate the filter, you have to add it to the _cp_filters attribute (a list) of your root controller:
class Root(controllers.RootController): # attach cherrypy filters _cp_filters = [SkinFilter()] ...
The filter can also be attached to non-root controllers so only parts of your application are affected by the filter.