The Hand of FuManChu

Gordon Tillman has a wiki page up on how to mix Django content into a CherryPy site. It's easy and probably works, but please don't do it anymore.

We're officially going to deprecate the wsgiapp Tool because 1) it doesn't conform to the WSGI spec (and cannot be fixed to do so), and 2) there's a better way to mix content in a CherryPy site: tree.graft.

The tree.graft(app, script_name) method is the proper way to add Django or other WSGI content to an existing CherryPy site. Instead of nesting the two frameworks, we branch instead. To take Gordon's example, instead of:

class DjangoApp(object):
    _cp_config = {
        'tools.wsgiapp.on': True,
        'tools.wsgiapp.app': AdminMediaHandler(WSGIHandler()),
}
...
cherrypy.tree.mount(DjangoApp(), '/')

You should always write this instead:

cherrypy.tree.graft(AdminMediaHandler(WSGIHandler()), '/')

Look, if you nest the one inside the other, CherryPy's going to do an awful lot of HTTP request parsing that is going to be completely redundant, since Django's going to do it again anyway. And this code is not very fast. Your site is going to crawl. That's strike one for nesting.

Strike two is the "always on" nature of nesting as opposed to branching. When you write your request/response cycle like an onion, every component which could possibly play a part in the request has to be called, even if just to reply "I'm not involved in this one". Given the slowness of Python function calls, this is rarely a good thing. If you thought your site was crawling before... This was a major design flaw of CherryPy 2, and is a major reason CherryPy 3 is 3x faster: the old Filters were called all the time, even if you didn't need them; the new Tools are only called when they're applicable.

Strike three against the nested approach is that it's always easier to traverse a tree of siblings than it is to traverse a nested set; programmers, for some reason, like to hide information from you, including how their site components go together. The branched version will be much easier to reason about, statically analyze, and write inspection tools for.

So please, use tree.graft, and stop using the wsgiapp Tool in CherryPy 3. We're going to formally deprecate it soon.