# Dynamic URL Dispatch

In the previous example we covered how to statically configure Twisted Web to serve different content at different URLs. The goal of this example is to show you how to do this dynamically instead. Reading the previous installment if you haven’t already is suggested in order to get an overview of how URLs are treated when using Twisted Web’s `resource` APIs.

`Site` (the object which associates a listening server port with the HTTP implementation), `Resource` (a convenient base class to use when defining custom pages), `reactor` (the object which implements the Twisted main loop), and `endpoints` return once again:

    from twisted.web.server import Site
    from twisted.web.resource import Resource
    from twisted.internet import reactor, endpoints

With that out of the way, here’s the interesting part of this example. We’re going to define a resource which renders a whole-year calendar. The year it will render the calendar for will be the year in the request URL. So, for example, `/2009` will render a calendar for 2009. First, here’s a resource that renders a calendar for the year passed to its initializer:

    from calendar import calendar

    class YearPage(Resource):
        def __init__(self, year):
            Resource.__init__(self)
            self.year = year

        def render_GET(self, request):
            cal = calendar(self.year)
            return (b"<!DOCTYPE html><html><head><meta charset='utf-8'>"
                    b"<title></title></head><body><pre>" + cal.encode('utf-8') + b"</pre>")

Pretty simple - not all that different from the first dynamic resource demonstrated in Generating a Page Dynamically . Now here’s the resource that handles URLs with a year in them by creating a suitable instance of this `YearPage` class:

    class Calendar(Resource):
      def getChild(self, name, request):
          return YearPage(int(name))

By implementing `getChild` here, we’ve just defined how Twisted Web should find children of `Calendar` instances when it’s resolving an URL into a resource. This implementation defines all integers as the children of `Calendar` (and punts on error handling, more on that later).

All that’s left is to create a `Site` using this resource as its root and then start the reactor:

    root = Calendar()
    factory = Site(root)
    endpoint = endpoints.TCP4ServerEndpoint(reactor, 8880)
    endpoint.listen(factory)
    reactor.run()

And that’s all. Any resource-based dynamic URL handling is going to look basically like `Calendar.getChild` . Here’s the full example code:

    from twisted.web.server import Site
    from twisted.web.resource import Resource
    from twisted.internet import reactor, endpoints

    from calendar import calendar

    class YearPage(Resource):
        def __init__(self, year):
            Resource.__init__(self)
            self.year = year

        def render_GET(self, request):
            cal = calendar(self.year)
            return (b"<!DOCTYPE html><html><head><meta charset='utf-8'>"
                    b"<title></title></head><body><pre>" + cal.encode('utf-8') + b"</pre>")

    class Calendar(Resource):
      def getChild(self, name, request):
          return YearPage(int(name))

    root = Calendar()
    factory = Site(root)
    endpoint = endpoints.TCP4ServerEndpoint(reactor, 8880)
    endpoint.listen(factory)
    reactor.run()