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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>The Zope 3 Component Architecture (Socket Example) — zope.configuration 4.0 documentation</title> <link rel="stylesheet" href="_static/default.css" type="text/css" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '', VERSION: '4.0', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="_static/jquery.js"></script> <script type="text/javascript" src="_static/underscore.js"></script> <script type="text/javascript" src="_static/doctools.js"></script> <link rel="top" title="zope.configuration 4.0 documentation" href="index.html" /> <link rel="next" title="Events" href="event.html" /> <link rel="prev" title="Zope Component Architecture" href="narr.html" /> </head> <body> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="event.html" title="Events" accesskey="N">next</a> |</li> <li class="right" > <a href="narr.html" title="Zope Component Architecture" accesskey="P">previous</a> |</li> <li><a href="index.html">zope.configuration 4.0 documentation</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="the-zope-3-component-architecture-socket-example"> <h1>The Zope 3 Component Architecture (Socket Example)<a class="headerlink" href="#the-zope-3-component-architecture-socket-example" title="Permalink to this headline">¶</a></h1> <p>The component architecture provides an application framework that provides its functionality through loosely-connected components. A <em>component</em> can be any Python object and has a particular purpose associated with it. Thus, in a component-based applications you have many small component in contrast to classical object-oriented development, where you have a few big objects.</p> <p>Components communicate via specific APIs, which are formally defined by interfaces, which are provided by the <cite>zope.interface</cite> package. <em>Interfaces</em> describe the methods and properties that a component is expected to provide. They are also used as a primary mean to provide developer-level documentation for the components. For more details about interfaces see <cite>zope/interface/README.txt</cite>.</p> <p>The two main types of components are <em>adapters</em> and <em>utilities</em>. They will be discussed in detail later in this document. Both component types are managed by the <em>site manager</em>, with which you can register and access these components. However, most of the site manager’s functionality is hidden behind the component architecture’s public API, which is documented in <cite>IComponentArchitecture</cite>.</p> <div class="section" id="adapters"> <h2>Adapters<a class="headerlink" href="#adapters" title="Permalink to this headline">¶</a></h2> <p>Adapters are a well-established pattern. An <em>adapter</em> uses an object providing one interface to produce an object that provides another interface. Here an example: Imagine that you purchased an electric shaver in the US, and thus you require the US socket type. You are now traveling in Germany, where another socket style is used. You will need a device, an adapter, that converts from the German to the US socket style.</p> <p>The functionality of adapters is actually natively provided by the <cite>zope.interface</cite> package and is thus well documented there. The <cite>human.txt</cite> file provides a gentle introduction to adapters, whereby <cite>adapter.txt</cite> is aimed at providing a comprehensive insight into adapters, but is too abstract for many as an initial read. Thus, we will only explain adapters in the context of the component architecture’s API.</p> <p>So let’s say that we have a German socket:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.interface</span> <span class="kn">import</span> <span class="n">Interface</span><span class="p">,</span> <span class="n">implements</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">IGermanSocket</span><span class="p">(</span><span class="n">Interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">Socket</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="s">'<instance of </span><span class="si">%s</span><span class="s">>'</span> <span class="o">%</span><span class="bp">self</span><span class="o">.</span><span class="n">__class__</span><span class="o">.</span><span class="n">__name__</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">GermanSocket</span><span class="p">(</span><span class="n">Socket</span><span class="p">):</span> <span class="gp">... </span> <span class="sd">"""German wall socket."""</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IGermanSocket</span><span class="p">)</span> </pre></div> </div> <p>and we want to convert it to an US socket</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">IUSSocket</span><span class="p">(</span><span class="n">Interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> </pre></div> </div> <p>so that our shaver can be used in Germany. So we go to a German electronics store to look for an adapter that we can plug in the wall:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">GermanToUSSocketAdapter</span><span class="p">(</span><span class="n">Socket</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">)</span> <span class="gp">... </span> <span class="n">__used_for__</span> <span class="o">=</span> <span class="n">IGermanSocket</span> <span class="gp">...</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">socket</span><span class="p">):</span> <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">context</span> <span class="o">=</span> <span class="n">socket</span> </pre></div> </div> <p>Note that I could have called the passed in socket any way I like, but <cite>context</cite> is the standard name accepted.</p> <div class="section" id="single-adapters"> <h3>Single Adapters<a class="headerlink" href="#single-adapters" title="Permalink to this headline">¶</a></h3> <p>Before we can use the adapter, we have to buy it and make it part of our inventory. In the component architecture we do this by registering the adapter with the framework, more specifically with the global site manager:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">zope.component</span> <span class="gp">>>> </span><span class="n">gsm</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getGlobalSiteManager</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerAdapter</span><span class="p">(</span><span class="n">GermanToUSSocketAdapter</span><span class="p">,</span> <span class="p">(</span><span class="n">IGermanSocket</span><span class="p">,),</span> <span class="n">IUSSocket</span><span class="p">)</span> </pre></div> </div> <p><cite>zope.component</cite> is the component architecture API that is being presented by this file. You registered an adapter from <cite>IGermanSocket</cite> to <cite>IUSSocket</cite> having no name (thus the empty string).</p> <p>Anyways, you finally get back to your hotel room and shave, since you have not been able to shave in the plane. In the bathroom you discover a socket:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">bathroomDE</span> <span class="o">=</span> <span class="n">GermanSocket</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">IGermanSocket</span><span class="o">.</span><span class="n">providedBy</span><span class="p">(</span><span class="n">bathroomDE</span><span class="p">)</span> <span class="go">True</span> </pre></div> </div> <p>You now insert the adapter in the German socket</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">bathroomUS</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAdapter</span><span class="p">(</span><span class="n">bathroomDE</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">''</span><span class="p">)</span> </pre></div> </div> <p>so that the socket now provides the US version:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">IUSSocket</span><span class="o">.</span><span class="n">providedBy</span><span class="p">(</span><span class="n">bathroomUS</span><span class="p">)</span> <span class="go">True</span> </pre></div> </div> <p>Now you can insert your shaver and get on with your day.</p> <p>After a week you travel for a couple of days to the Prague and you notice that the Czech have yet another socket type:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">ICzechSocket</span><span class="p">(</span><span class="n">Interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">CzechSocket</span><span class="p">(</span><span class="n">Socket</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">ICzechSocket</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">czech</span> <span class="o">=</span> <span class="n">CzechSocket</span><span class="p">()</span> </pre></div> </div> <p>You try to find an adapter for your shaver in your bag, but you fail, since you do not have one:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAdapter</span><span class="p">(</span><span class="n">czech</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">''</span><span class="p">)</span> \ <span class="gp">... </span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ComponentLookupError</span>: <span class="n">(<instance of CzechSocket>,</span> <span class="go"> <InterfaceClass __builtin__.IUSSocket>,</span> <span class="go"> '')</span> </pre></div> </div> <p>or the more graceful way:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">marker</span> <span class="o">=</span> <span class="nb">object</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">socket</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">queryAdapter</span><span class="p">(</span><span class="n">czech</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">''</span><span class="p">,</span> <span class="n">marker</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">socket</span> <span class="ow">is</span> <span class="n">marker</span> <span class="go">True</span> </pre></div> </div> <p>In the component architecture API any <cite>get*</cite> method will fail with a specific exception, if a query failed, whereby methods starting with <cite>query*</cite> will always return a <cite>default</cite> value after a failure.</p> </div> <div class="section" id="named-adapters"> <h3>Named Adapters<a class="headerlink" href="#named-adapters" title="Permalink to this headline">¶</a></h3> <p>You are finally back in Germany. You also brought your DVD player and a couple DVDs with you, which you would like to watch. Your shaver was able to convert automatically from 110 volts to 240 volts, but your DVD player cannot. So you have to buy another adapter that also handles converting the voltage and the frequency of the AC current:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">GermanToUSSocketAdapterAndTransformer</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">)</span> <span class="gp">... </span> <span class="n">__used_for__</span> <span class="o">=</span> <span class="n">IGermanSocket</span> <span class="gp">...</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">socket</span><span class="p">):</span> <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">context</span> <span class="o">=</span> <span class="n">socket</span> </pre></div> </div> <p>Now, we need a way to keep the two adapters apart. Thus we register them with a name:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerAdapter</span><span class="p">(</span><span class="n">GermanToUSSocketAdapter</span><span class="p">,</span> <span class="gp">... </span> <span class="p">(</span><span class="n">IGermanSocket</span><span class="p">,),</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'shaver'</span><span class="p">,)</span> <span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerAdapter</span><span class="p">(</span><span class="n">GermanToUSSocketAdapterAndTransformer</span><span class="p">,</span> <span class="gp">... </span> <span class="p">(</span><span class="n">IGermanSocket</span><span class="p">,),</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'dvd'</span><span class="p">)</span> </pre></div> </div> <p>Now we simply look up the adapters using their labels (called <em>name</em>):</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">socket</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAdapter</span><span class="p">(</span><span class="n">bathroomDE</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'shaver'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">socket</span><span class="o">.</span><span class="n">__class__</span> <span class="ow">is</span> <span class="n">GermanToUSSocketAdapter</span> <span class="go">True</span> <span class="gp">>>> </span><span class="n">socket</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAdapter</span><span class="p">(</span><span class="n">bathroomDE</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'dvd'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">socket</span><span class="o">.</span><span class="n">__class__</span> <span class="ow">is</span> <span class="n">GermanToUSSocketAdapterAndTransformer</span> <span class="go">True</span> </pre></div> </div> <p>Clearly, we do not have an adapter for the MP3 player</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAdapter</span><span class="p">(</span><span class="n">bathroomDE</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'mp3'</span><span class="p">)</span> \ <span class="gp">... </span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ComponentLookupError</span>: <span class="n">(<instance of GermanSocket>,</span> <span class="go"> <InterfaceClass __builtin__.IUSSocket>,</span> <span class="go"> 'mp3')</span> </pre></div> </div> <p>but you could use the ‘dvd’ adapter in this case of course. ;)</p> <p>Sometimes you want to know all adapters that are available. Let’s say you want to know about all the adapters that convert a German to a US socket type:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">sockets</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAdapters</span><span class="p">((</span><span class="n">bathroomDE</span><span class="p">,),</span> <span class="n">IUSSocket</span><span class="p">))</span> <span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">sockets</span><span class="p">)</span> <span class="go">3</span> <span class="gp">>>> </span><span class="n">names</span> <span class="o">=</span> <span class="p">[</span><span class="n">name</span> <span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">socket</span> <span class="ow">in</span> <span class="n">sockets</span><span class="p">]</span> <span class="gp">>>> </span><span class="n">names</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">names</span> <span class="go">[u'', u'dvd', u'shaver']</span> </pre></div> </div> <p><cite>zope.component.getAdapters()</cite> returns a list of tuples. The first entry of the tuple is the name of the adapter and the second is the adapter itself.</p> </div> <div class="section" id="multi-adapters"> <h3>Multi-Adapters<a class="headerlink" href="#multi-adapters" title="Permalink to this headline">¶</a></h3> <p>After watching all the DVDs you brought at least twice, you get tired of them and you want to listen to some music using your MP3 player. But darn, the MP3 player plug has a ground pin and all the adapters you have do not support that:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">IUSGroundedSocket</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> </pre></div> </div> <p>So you go out another time to buy an adapter. This time, however, you do not buy yet another adapter, but a piece that provides the grounding plug:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">IGrounder</span><span class="p">(</span><span class="n">Interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">Grounder</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IGrounder</span><span class="p">)</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="s">'<instance of Grounder>'</span> </pre></div> </div> <p>Then together they will provided a grounded us socket:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">GroundedGermanToUSSocketAdapter</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IUSGroundedSocket</span><span class="p">)</span> <span class="gp">... </span> <span class="n">__used_for__</span> <span class="o">=</span> <span class="p">(</span><span class="n">IGermanSocket</span><span class="p">,</span> <span class="n">IGrounder</span><span class="p">)</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">socket</span><span class="p">,</span> <span class="n">grounder</span><span class="p">):</span> <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">socket</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">grounder</span> <span class="o">=</span> <span class="n">socket</span><span class="p">,</span> <span class="n">grounder</span> </pre></div> </div> <p>You now register the combination, so that you know you can create a <cite>IUSGroundedSocket</cite>:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerAdapter</span><span class="p">(</span><span class="n">GroundedGermanToUSSocketAdapter</span><span class="p">,</span> <span class="gp">... </span> <span class="p">(</span><span class="n">IGermanSocket</span><span class="p">,</span> <span class="n">IGrounder</span><span class="p">),</span> <span class="n">IUSGroundedSocket</span><span class="p">,</span> <span class="s">'mp3'</span><span class="p">)</span> </pre></div> </div> <p>Given the grounder</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">grounder</span> <span class="o">=</span> <span class="n">Grounder</span><span class="p">()</span> </pre></div> </div> <p>and a German socket</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">livingroom</span> <span class="o">=</span> <span class="n">GermanSocket</span><span class="p">()</span> </pre></div> </div> <p>we can now get a grounded US socket:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">socket</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getMultiAdapter</span><span class="p">((</span><span class="n">livingroom</span><span class="p">,</span> <span class="n">grounder</span><span class="p">),</span> <span class="gp">... </span> <span class="n">IUSGroundedSocket</span><span class="p">,</span> <span class="s">'mp3'</span><span class="p">)</span> </pre></div> </div> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">socket</span><span class="o">.</span><span class="n">__class__</span> <span class="ow">is</span> <span class="n">GroundedGermanToUSSocketAdapter</span> <span class="go">True</span> <span class="gp">>>> </span><span class="n">socket</span><span class="o">.</span><span class="n">socket</span> <span class="ow">is</span> <span class="n">livingroom</span> <span class="go">True</span> <span class="gp">>>> </span><span class="n">socket</span><span class="o">.</span><span class="n">grounder</span> <span class="ow">is</span> <span class="n">grounder</span> <span class="go">True</span> </pre></div> </div> <p>Of course, you do not have a ‘dvd’ grounded US socket available:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getMultiAdapter</span><span class="p">((</span><span class="n">livingroom</span><span class="p">,</span> <span class="n">grounder</span><span class="p">),</span> <span class="gp">... </span> <span class="n">IUSGroundedSocket</span><span class="p">,</span> <span class="s">'dvd'</span><span class="p">)</span> \ <span class="gp">... </span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ComponentLookupError</span>: <span class="n">((<instance of GermanSocket>,</span> <span class="go"> <instance of Grounder>),</span> <span class="go"> <InterfaceClass __builtin__.IUSGroundedSocket>,</span> <span class="go"> 'dvd')</span> </pre></div> </div> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">socket</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">queryMultiAdapter</span><span class="p">(</span> <span class="gp">... </span> <span class="p">(</span><span class="n">livingroom</span><span class="p">,</span> <span class="n">grounder</span><span class="p">),</span> <span class="n">IUSGroundedSocket</span><span class="p">,</span> <span class="s">'dvd'</span><span class="p">,</span> <span class="n">marker</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">socket</span> <span class="ow">is</span> <span class="n">marker</span> <span class="go">True</span> </pre></div> </div> <p>Again, you might want to read <cite>adapter.txt</cite> in <cite>zope.interface</cite> for a more comprehensive coverage of multi-adapters.</p> </div> </div> <div class="section" id="subscribers"> <h2>Subscribers<a class="headerlink" href="#subscribers" title="Permalink to this headline">¶</a></h2> <p>While subscribers are directly supported by the adapter registry and are adapters for all theoretical purposes, practically it might be better to think of them as separate components. Subscribers are particularly useful for events.</p> <p>Let’s say one of our adapters overheated and caused a small fire:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">IFire</span><span class="p">(</span><span class="n">Interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">Fire</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IFire</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">fire</span> <span class="o">=</span> <span class="n">Fire</span><span class="p">()</span> </pre></div> </div> <p>We want to use all available objects to put out the fire:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">IFireExtinguisher</span><span class="p">(</span><span class="n">Interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">extinguish</span><span class="p">():</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">FireExtinguisher</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">fire</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">extinguish</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="s">"Place extinguish code here."</span> <span class="gp">... </span> <span class="k">print</span> <span class="s">'Used '</span> <span class="o">+</span> <span class="bp">self</span><span class="o">.</span><span class="n">__class__</span><span class="o">.</span><span class="n">__name__</span> <span class="o">+</span> <span class="s">'.'</span> </pre></div> </div> <p>Here some specific methods to put out the fire:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">PowderExtinguisher</span><span class="p">(</span><span class="n">FireExtinguisher</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerSubscriptionAdapter</span><span class="p">(</span><span class="n">PowderExtinguisher</span><span class="p">,</span> <span class="gp">... </span> <span class="p">(</span><span class="n">IFire</span><span class="p">,),</span> <span class="n">IFireExtinguisher</span><span class="p">)</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">Blanket</span><span class="p">(</span><span class="n">FireExtinguisher</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerSubscriptionAdapter</span><span class="p">(</span><span class="n">Blanket</span><span class="p">,</span> <span class="p">(</span><span class="n">IFire</span><span class="p">,),</span> <span class="n">IFireExtinguisher</span><span class="p">)</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">SprinklerSystem</span><span class="p">(</span><span class="n">FireExtinguisher</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerSubscriptionAdapter</span><span class="p">(</span><span class="n">SprinklerSystem</span><span class="p">,</span> <span class="gp">... </span> <span class="p">(</span><span class="n">IFire</span><span class="p">,),</span> <span class="n">IFireExtinguisher</span><span class="p">)</span> </pre></div> </div> <p>Now let use all these things to put out the fire:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">extinguishers</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">subscribers</span><span class="p">((</span><span class="n">fire</span><span class="p">,),</span> <span class="n">IFireExtinguisher</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">extinguishers</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span> <span class="gp">>>> </span><span class="k">for</span> <span class="n">extinguisher</span> <span class="ow">in</span> <span class="n">extinguishers</span><span class="p">:</span> <span class="gp">... </span> <span class="n">extinguisher</span><span class="o">.</span><span class="n">extinguish</span><span class="p">()</span> <span class="go">Used Blanket.</span> <span class="go">Used PowderExtinguisher.</span> <span class="go">Used SprinklerSystem.</span> </pre></div> </div> <p>If no subscribers are found for a particular object, then an empty list is returned:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">subscribers</span><span class="p">((</span><span class="nb">object</span><span class="p">(),),</span> <span class="n">IFireExtinguisher</span><span class="p">)</span> <span class="go">[]</span> </pre></div> </div> </div> <div class="section" id="utilities"> <h2>Utilities<a class="headerlink" href="#utilities" title="Permalink to this headline">¶</a></h2> <p>Utilities are the second type of component, the component architecture implements. <em>Utilities</em> are simply components that provide an interface. When you register an utility, you always register an instance (in contrast to a factory for adapters) since the initialization and setup process of a utility might be complex and is not well defined. In some ways a utility is much more fundamental than an adapter, because an adapter cannot be used without another component, but a utility is always self-contained. I like to think of utilities as the foundation of your application and adapters as components extending beyond this foundation.</p> <p>Back to our story...</p> <p>After your vacation is over you fly back home to Tampa, Florida. But it is August now, the middle of the Hurricane season. And, believe it or not, you are worried that you will not be able to shave when the power goes out for several days. (You just hate wet shavers.)</p> <p>So you decide to go to your favorite hardware store and by a Diesel-powered electric generator. The generator provides of course a US-style socket:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Generator</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">)</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="s">'<instance of Generator>'</span> <span class="gp">>>> </span><span class="n">generator</span> <span class="o">=</span> <span class="n">Generator</span><span class="p">()</span> </pre></div> </div> <p>Like for adapters, we now have to add the newly-acquired generator to our inventory by registering it as a utility:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerUtility</span><span class="p">(</span><span class="n">generator</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">)</span> </pre></div> </div> <p>We can now get the utility using</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">utility</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getUtility</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">utility</span> <span class="ow">is</span> <span class="n">generator</span> <span class="go">True</span> </pre></div> </div> <p>As you can see, it is very simple to register and retrieve utilities. If a utility does not exist for a particular interface, such as the German socket, then the lookup fails</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getUtility</span><span class="p">(</span><span class="n">IGermanSocket</span><span class="p">)</span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ComponentLookupError</span>: <span class="n">(<InterfaceClass __builtin__.IGermanSocket>, '')</span> </pre></div> </div> <p>or more gracefully when specifying a default value:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">default</span> <span class="o">=</span> <span class="nb">object</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">utility</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">queryUtility</span><span class="p">(</span><span class="n">IGermanSocket</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="n">default</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">utility</span> <span class="ow">is</span> <span class="n">default</span> <span class="go">True</span> </pre></div> </div> <p>Note: The only difference between <cite>getUtility()</cite> and <cite>queryUtility()</cite> is the fact that you can specify a default value for the latter function, so that it will never cause a <cite>ComponentLookupError</cite>.</p> <div class="section" id="named-utilities"> <h3>Named Utilities<a class="headerlink" href="#named-utilities" title="Permalink to this headline">¶</a></h3> <p>It is often desirable to have several utilities providing the same interface per site. This way you can implement any sort of registry using utilities. For this reason, utilities – like adapters – can be named.</p> <p>In the context of our story, we might want to do the following: You really do not trust gas stations either. What if the roads are blocked after a hurricane and the gas stations run out of oil. So you look for another renewable power source. Then you think about solar panels! After a storm there is usually very nice weather, so why not? Via the Web you order a set of 110V/120W solar panels that provide a regular US-style socket as output:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">SolarPanel</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="n">implements</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">)</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="s">'<instance of Solar Panel>'</span> <span class="gp">>>> </span><span class="n">panel</span> <span class="o">=</span> <span class="n">SolarPanel</span><span class="p">()</span> </pre></div> </div> <p>Once it arrives, we add it to our inventory:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerUtility</span><span class="p">(</span><span class="n">panel</span><span class="p">,</span> <span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'Solar Panel'</span><span class="p">)</span> </pre></div> </div> <p>You can now access the solar panel using</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">utility</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getUtility</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'Solar Panel'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">utility</span> <span class="ow">is</span> <span class="n">panel</span> <span class="go">True</span> </pre></div> </div> <p>Of course, if a utility is not available, then the lookup will simply fail</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getUtility</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'Wind Mill'</span><span class="p">)</span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ComponentLookupError</span>: <span class="n">(<InterfaceClass __builtin__.IUSSocket>, 'Wind Mill')</span> </pre></div> </div> <p>or more gracefully when specifying a default value:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">default</span> <span class="o">=</span> <span class="nb">object</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">utility</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">queryUtility</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">,</span> <span class="s">'Wind Mill'</span><span class="p">,</span> <span class="gp">... </span> <span class="n">default</span><span class="o">=</span><span class="n">default</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">utility</span> <span class="ow">is</span> <span class="n">default</span> <span class="go">True</span> </pre></div> </div> <p>Now you want to look at all the utilities you have for a particular kind. The following API function will return a list of name/utility pairs:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">utils</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getUtilitiesFor</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">))</span> <span class="gp">>>> </span><span class="n">utils</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">utils</span> <span class="go">[(u'', <instance of Generator>),</span> <span class="go"> (u'Solar Panel', <instance of Solar Panel>)]</span> </pre></div> </div> <p>Another method of looking up all utilities is by using <cite>getAllUtilitiesRegisteredFor(iface)</cite>. This function will return an iterable of utilities (without names); however, it will also return overridden utilities. If you are not using multiple site managers, you will not actually need this method.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">utils</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getAllUtilitiesRegisteredFor</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">))</span> <span class="gp">>>> </span><span class="n">utils</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">utils</span> <span class="go">[<instance of Generator>, <instance of Solar Panel>]</span> </pre></div> </div> </div> <div class="section" id="factories"> <h3>Factories<a class="headerlink" href="#factories" title="Permalink to this headline">¶</a></h3> <p>A <em>factory</em> is a special kind of utility that exists to create other components. A factory is always identified by a name. It also provides a title and description and is able to tell the developer what interfaces the created object will provide. The advantage of using a factory to create an object instead of directly instantiating a class or executing any other callable is that we can refer to the factory by name. As long as the name stays fixed, the implementation of the callable can be renamed or moved without a breakage in code.</p> <p>Let’s say that our solar panel comes in parts and they have to be assembled. This assembly would be done by a factory, so let’s create one for the solar panel. To do this, we can use a standard implementation of the <cite>IFactory</cite> interface:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.factory</span> <span class="kn">import</span> <span class="n">Factory</span> <span class="gp">>>> </span><span class="n">factory</span> <span class="o">=</span> <span class="n">Factory</span><span class="p">(</span><span class="n">SolarPanel</span><span class="p">,</span> <span class="gp">... </span> <span class="s">'Solar Panel'</span><span class="p">,</span> <span class="gp">... </span> <span class="s">'This factory creates a solar panel.'</span><span class="p">)</span> </pre></div> </div> <p>Optionally, I could have also specified the interfaces that the created object will provide, but the factory class is smart enough to determine the implemented interface from the class. We now register the factory:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.interfaces</span> <span class="kn">import</span> <span class="n">IFactory</span> <span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerUtility</span><span class="p">(</span><span class="n">factory</span><span class="p">,</span> <span class="n">IFactory</span><span class="p">,</span> <span class="s">'SolarPanel'</span><span class="p">)</span> </pre></div> </div> <p>We can now get a list of interfaces the produced object will provide:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">ifaces</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getFactoryInterfaces</span><span class="p">(</span><span class="s">'SolarPanel'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">IUSSocket</span> <span class="ow">in</span> <span class="n">ifaces</span> <span class="go">True</span> </pre></div> </div> <p>By the way, this is equivalent to</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">ifaces2</span> <span class="o">=</span> <span class="n">factory</span><span class="o">.</span><span class="n">getInterfaces</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">ifaces</span> <span class="ow">is</span> <span class="n">ifaces2</span> <span class="go">True</span> </pre></div> </div> <p>Of course you can also just create an object:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">panel</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">createObject</span><span class="p">(</span><span class="s">'SolarPanel'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">panel</span><span class="o">.</span><span class="n">__class__</span> <span class="ow">is</span> <span class="n">SolarPanel</span> <span class="go">True</span> </pre></div> </div> <p>Note: Ignore the first argument (<cite>None</cite>) for now; it is the context of the utility lookup, which is usually an optional argument, but cannot be in this case, since all other arguments beside the <cite>name</cite> are passed in as arguments to the specified callable.</p> <p>Once you register several factories</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">gsm</span><span class="o">.</span><span class="n">registerUtility</span><span class="p">(</span><span class="n">Factory</span><span class="p">(</span><span class="n">Generator</span><span class="p">),</span> <span class="n">IFactory</span><span class="p">,</span> <span class="s">'Generator'</span><span class="p">)</span> </pre></div> </div> <p>you can also determine, which available factories will create objects providing a certain interface:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">factories</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getFactoriesFor</span><span class="p">(</span><span class="n">IUSSocket</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">factories</span> <span class="o">=</span> <span class="p">[(</span><span class="n">name</span><span class="p">,</span> <span class="n">factory</span><span class="o">.</span><span class="n">__class__</span><span class="p">)</span> <span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">factory</span> <span class="ow">in</span> <span class="n">factories</span><span class="p">]</span> <span class="gp">>>> </span><span class="n">factories</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">factories</span> <span class="go">[(u'Generator', <class 'zope.component.factory.Factory'>),</span> <span class="go"> (u'SolarPanel', <class 'zope.component.factory.Factory'>)]</span> </pre></div> </div> </div> </div> <div class="section" id="site-managers"> <h2>Site Managers<a class="headerlink" href="#site-managers" title="Permalink to this headline">¶</a></h2> <p>Why do we need site managers? Why is the component architecture API not sufficient? Some applications, including Zope 3, have a concept of locations. It is often desirable to have different configurations for these location; this can be done by overwriting existing or adding new component registrations. Site managers in locations below the root location, should be able to delegate requests to their parent locations. The root site manager is commonly known as <em>global site manager</em>, since it is always available. You can always get the global site manager using the API:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">gsm</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getGlobalSiteManager</span><span class="p">()</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component</span> <span class="kn">import</span> <span class="n">globalSiteManager</span> <span class="gp">>>> </span><span class="n">gsm</span> <span class="ow">is</span> <span class="n">globalSiteManager</span> <span class="go">True</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.interfaces</span> <span class="kn">import</span> <span class="n">IComponentLookup</span> <span class="gp">>>> </span><span class="n">IComponentLookup</span><span class="o">.</span><span class="n">providedBy</span><span class="p">(</span><span class="n">gsm</span><span class="p">)</span> <span class="go">True</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.interfaces</span> <span class="kn">import</span> <span class="n">IComponents</span> <span class="gp">>>> </span><span class="n">IComponents</span><span class="o">.</span><span class="n">providedBy</span><span class="p">(</span><span class="n">gsm</span><span class="p">)</span> <span class="go">True</span> </pre></div> </div> <p>You can also lookup at site manager in a given context. The only requirement is that the context can be adapted to a site manager. So let’s create a special site manager:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.globalregistry</span> <span class="kn">import</span> <span class="n">BaseGlobalComponents</span> <span class="gp">>>> </span><span class="n">sm</span> <span class="o">=</span> <span class="n">BaseGlobalComponents</span><span class="p">()</span> </pre></div> </div> <p>Now we create a context that adapts to the site manager via the <cite>__conform__</cite> method as specified in PEP 246.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Context</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">sm</span><span class="p">):</span> <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">sm</span> <span class="o">=</span> <span class="n">sm</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__conform__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">interface</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="n">interface</span><span class="o">.</span><span class="n">isOrExtends</span><span class="p">(</span><span class="n">IComponentLookup</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">sm</span> </pre></div> </div> <p>We now instantiate the <cite>Context</cite> with our special site manager:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">Context</span><span class="p">(</span><span class="n">sm</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">sm</span> <span class="ow">is</span> <span class="n">sm</span> <span class="go">True</span> </pre></div> </div> <p>We can now ask for the site manager of this context:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">lsm</span> <span class="o">=</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">getSiteManager</span><span class="p">(</span><span class="n">context</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">lsm</span> <span class="ow">is</span> <span class="n">sm</span> <span class="go">True</span> </pre></div> </div> <p>The site manager instance <cite>lsm</cite> is formally known as a <em>local site manager</em> of <cite>context</cite>.</p> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="index.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">The Zope 3 Component Architecture (Socket Example)</a><ul> <li><a class="reference internal" href="#adapters">Adapters</a><ul> <li><a class="reference internal" href="#single-adapters">Single Adapters</a></li> <li><a class="reference internal" href="#named-adapters">Named Adapters</a></li> <li><a class="reference internal" href="#multi-adapters">Multi-Adapters</a></li> </ul> </li> <li><a class="reference internal" href="#subscribers">Subscribers</a></li> <li><a class="reference internal" href="#utilities">Utilities</a><ul> <li><a class="reference internal" href="#named-utilities">Named Utilities</a></li> <li><a class="reference internal" href="#factories">Factories</a></li> </ul> </li> <li><a class="reference internal" 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