~justin-fathomdb/nova/justinsb-openstack-api-volumes

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<title>Twisted Documentation: Dynamic URL Dispatch</title>

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<h1 class="title">Dynamic URL Dispatch</h1>

In the <a href="static-dispatch.html" shape="rect">previous example</a> 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 <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.html" title="twisted.web.resource">resource</a></code> APIs.

<code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.server.Site.html" title="twisted.web.server.Site">Site</a></code> (the object which

associates a listening server port with the HTTP implementation), <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.Resource.html" title="twisted.web.resource.Resource">Resource</a></code> (a convenient base class

to use when defining custom pages), and <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.internet.reactor.html" title="twisted.internet.reactor">reactor</a></code> (the object which implements the Twisted

main loop) return once again:

<pre class="python">1

from twisted.web.server import Site

from twisted.web.resource import Resource

from twisted.internet import reactor

</pre>

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,

<code>/2009</code> will render a calendar for 2009. First, here's a resource

that renders a calendar for the year passed to its initializer:

<pre class="python">1

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),)

</pre>

Pretty simple - not all that different from the first dynamic resource

demonstrated in <a href="dynamic-content.html" shape="rect">Generating a Page

Dynamically</a>. Now here's the resource that handles URLs with a year in them

by creating a suitable instance of this <code>YearPage</code> class:

<pre class="python">1

class Calendar(Resource):

def getChild(self, name, request):

return YearPage(int(name))

</pre>

By implementing <code class="API"><a href="http://twistedmatrix.com/documents/10.0.0/api/twisted.web.resource.Resource.getChild.html" title="twisted.web.resource.Resource.getChild">getChild</a></code> here, we've just defined

how Twisted Web should find children of <code>Calendar</code> instances when

it's resolving an URL into a resource. This implementation defines all integers

as the children of <code>Calendar</code> (and punts on error handling, more on

that later).

All that's left is to create a <code>Site</code> using this resource as its

root and then start the reactor:

root = Calendar()

factory = Site(root)

reactor.listenTCP(8880, factory)

reactor.run()

</pre>

And that's all. Any resource-based dynamic URL handling is going to look

basically like <code>Calendar.getPage</code>. Here's the full example code:

<pre class="python"> 1

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from calendar import calendar

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class YearPage(Resource):

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def __init__(self, year):

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Resource.__init__(self)

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self.year = year

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def render_GET(self, request):

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class Calendar(Resource):

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return YearPage(int(name))

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root = Calendar()

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factory = Site(root)

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reactor.listenTCP(8880, factory)

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reactor.run()

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</pre>

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