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<div class="section" id="session-basics">
<h1>Session Basics<a class="headerlink" href="#session-basics" title="Permalink to this headline">ΒΆ</a></h1>
<p>Sessions are the most complicated topic covered in this series of examples,
and because of that it is going to take a few examples to cover all of the
different aspects. This first example demonstrates the very basics of the
Twisted Web session API: how to get the session object for the current request
and how to prematurely expire a session.</p>
<p>Before diving into the APIs, let’s look at the big picture of
sessions in Twisted Web. Sessions are represented by instances
of <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.server.Session.html">Session</a> . The <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.server.Site.html">Site</a> creates a new instance
of <code class="docutils literal"><span class="pre">Session</span></code> the first time an application asks for it for
a particular session. <code class="docutils literal"><span class="pre">Session</span></code> instances are kept on
the <code class="docutils literal"><span class="pre">Site</span></code> instance until they expire (due to inactivity or
because they are explicitly expired). Each time after the first that a
particular session’s <code class="docutils literal"><span class="pre">Session</span></code> object is requested, it is
retrieved from the <code class="docutils literal"><span class="pre">Site</span></code> .</p>
<p>With the conceptual underpinnings of the upcoming API in place, here comes
the example. This will be a very simple <a class="reference internal" href="rpy-scripts.html"><em>rpy script</em></a> which tells a user what its unique session identifier is and lets it
prematurely expire the session.</p>
<p>First, we’ll import <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.resource.Resource.html">Resource</a> so we can define a couple of
subclasses of it:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">twisted.web.resource</span> <span class="kn">import</span> <span class="n">Resource</span>
</pre></div>
</div>
<p>Next we’ll define the resource which tells the client what its session
identifier is. This is done easily by first getting the session object
using <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.server.Request.getSession.html">Request.getSession</a> and
then getting the session object’s uid attribute:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">ShowSession</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">render_GET</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">request</span><span class="p">):</span>
<span class="k">return</span> <span class="s">'Your session id is: '</span> <span class="o">+</span> <span class="n">request</span><span class="o">.</span><span class="n">getSession</span><span class="p">()</span><span class="o">.</span><span class="n">uid</span>
</pre></div>
</div>
<p>To let the client expire its own session before it times out, we’ll define
another resource which expires whatever session it is requested with. This is
done using the <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.server.Session.expire.html">Session.expire</a>
method:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">ExpireSession</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">render_GET</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">request</span><span class="p">):</span>
<span class="n">request</span><span class="o">.</span><span class="n">getSession</span><span class="p">()</span><span class="o">.</span><span class="n">expire</span><span class="p">()</span>
<span class="k">return</span> <span class="s">'Your session has been expired.'</span>
</pre></div>
</div>
<p>Finally, to make the example an rpy script, we’ll make an instance
of <code class="docutils literal"><span class="pre">ShowSession</span></code> and give it an instance
of <code class="docutils literal"><span class="pre">ExpireSession</span></code> as a child using <a class="api reference external" href="https://twistedmatrix.com/documents/16.0.0/api/twisted.web.resource.Resource.putChild.html">Resource.putChild</a> :</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">resource</span> <span class="o">=</span> <span class="n">ShowSession</span><span class="p">()</span>
<span class="n">resource</span><span class="o">.</span><span class="n">putChild</span><span class="p">(</span><span class="s">"expire"</span><span class="p">,</span> <span class="n">ExpireSession</span><span class="p">())</span>
</pre></div>
</div>
<p>And that is the complete example. You can fire this up and load the top
page. You’ll see a (rather opaque) session identifier that remains the same
across reloads (at least until you flush the <code class="docutils literal"><span class="pre">TWISTED_SESSION</span></code> cookie
from your browser or enough time passes). You can then visit
the <code class="docutils literal"><span class="pre">expire</span></code> child and go back to the top page and see that you have
a new session.</p>
<p>Here’s the complete source for the example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">twisted.web.resource</span> <span class="kn">import</span> <span class="n">Resource</span>
<span class="k">class</span> <span class="nc">ShowSession</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">render_GET</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">request</span><span class="p">):</span>
<span class="k">return</span> <span class="s">'Your session id is: '</span> <span class="o">+</span> <span class="n">request</span><span class="o">.</span><span class="n">getSession</span><span class="p">()</span><span class="o">.</span><span class="n">uid</span>
<span class="k">class</span> <span class="nc">ExpireSession</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">render_GET</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">request</span><span class="p">):</span>
<span class="n">request</span><span class="o">.</span><span class="n">getSession</span><span class="p">()</span><span class="o">.</span><span class="n">expire</span><span class="p">()</span>
<span class="k">return</span> <span class="s">'Your session has been expired.'</span>
<span class="n">resource</span> <span class="o">=</span> <span class="n">ShowSession</span><span class="p">()</span>
<span class="n">resource</span><span class="o">.</span><span class="n">putChild</span><span class="p">(</span><span class="s">"expire"</span><span class="p">,</span> <span class="n">ExpireSession</span><span class="p">())</span>
</pre></div>
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