:LastChangedDate: $LastChangedDate$ :LastChangedRevision: $LastChangedRevision$ :LastChangedBy: $LastChangedBy$ Error Handling ============== In this example we'll extend dynamic dispatch to return a 404 (not found) response when a client requests a non-existent URL. As in the previous examples, we'll start with :api:`twisted.web.server.Site ` , :api:`twisted.web.resource.Resource ` , and :api:`twisted.internet.reactor ` imports: .. code-block:: python from twisted.web.server import Site from twisted.web.resource import Resource from twisted.internet import reactor Next, we'll add one more import. :api:`twisted.web.resource.NoResource ` is one of the pre-defined error resources provided by Twisted Web. It generates the necessary 404 response code and renders a simple html page telling the client there is no such resource. .. code-block:: python from twisted.web.resource import NoResource Next, we'll define a custom resource which does some dynamic URL dispatch. This example is going to be just like the :doc:`previous one ` , where the path segment is interpreted as a year; the difference is that this time we'll handle requests which don't conform to that pattern by returning the not found response: .. code-block:: python class Calendar(Resource): def getChild(self, name, request): try: year = int(name) except ValueError: return NoResource() else: return YearPage(year) Aside from including the definition of ``YearPage`` from the previous example, the only other thing left to do is the normal ``Site`` and ``reactor`` setup. Here's the complete code for this example: .. code-block:: python from twisted.web.server import Site from twisted.web.resource import Resource from twisted.internet import reactor from twisted.web.resource import NoResource from calendar import calendar class YearPage(Resource): def __init__(self, year): Resource.__init__(self) self.year = year def render_GET(self, request): return "

%s

" % (calendar(self.year),) class Calendar(Resource): def getChild(self, name, request): try: year = int(name) except ValueError: return NoResource() else: return YearPage(year) root = Calendar() factory = Site(root) reactor.listenTCP(8880, factory) reactor.run() This server hands out the same calendar views as the one from the previous installment, but it will also hand out a nice error page with a 404 response when a request is made for a URL which cannot be interpreted as a year.