Stylized line drawing of mark playing the flute

Basic page routing with CherryPy

My last CherryPy post covered how to set up a very basic site using the quickstart() function. This time, I'm going to go into some basic details on page handling..

The first thing we're going to do is define a class for handling the root of our site.

class Root:    def index(self):        return "This is the root" = Trueif __name__ == "__main__":    root = Root()    cherrypy.tree.mount(root, '/')    cherrypy.engine.start()    cherrypy.engine.block()

There's a lot going on in the above so let's break it down starting with the code that's actually running the site.

First we create an instance of the Root() class and mount it at the url '/'. Then we start the cherrypy engine. The default behavior in this case is for the site to run on port 8080 so our site is running on https://localhost:8080.

Hitting that url is going to call the index() of the Root() class. Note the = True line below the method. That's important because, without it, the method can't be called from outside the class.

Now let's add another url route.

if __name__ == "__main__":    root = Root()    root.names = NamesPage()    cherrypy.tree.mount(root, '/')    cherrypy.engine.start()    cherrypy.engine.block()

See the line starting with root.names =? That's going to set up a handler for the url https://localhost:8080/names.

Let's look at the definition of the NamesPage() class. The simplest would be something just like the Root() class.

class NamesPage:    def index(self):        return "This is the root" = True

But what if we also wanted to handle the url https://localhost:8080/names/help?

class NamesPage:    def index(self):        return "This is the names index" = True    def help(self):        return "This is the help page" = True

You can see how the first part of the request URI maps to the index method of the page handler class. The next part of the request URI maps to any method in the routing class with a matching name.

The next neat bit about routing comes into play when the last part of the URI doesn't match any defined methods. For example, how do we handle the url https://localhost:8080/names/mark?

As the NamesPage() class stands now, we'll end up with a 404 exception. But, by using the default() method in the NamesPage() class, we can handle it in a very cool way.

class NamesPage:    def default(self, name=None):       return "Hello " + name = True    def help(self):        return "This is the help page" = True

With this definition of NamesPage(), everything that comes after "/names/" (except for help/) gets passed as an argument to the default() method.

The above is a pretty simple summary. There's a lot more that can be done as you can see from the PageHandlers documentation.