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<div class="section" id="the-current-component-registry">
<h1>The current component registry<a class="headerlink" href="#the-current-component-registry" title="Permalink to this headline">¶</a></h1>
<p>There can be any number of component registries in an application. One of them
is the global component registry, and there is also the concept of a currently
used component registry. Component registries other than the global one are
associated with objects called sites. The <tt class="docutils literal"><span class="pre">zope.component.hooks</span></tt> module
provides an API to set and access the current site as well as manipulate the
adapter hook associated with it.</p>
<p>As long as we haven’t set a site, none is being considered current:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.hooks</span> <span class="kn">import</span> <span class="n">getSite</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">getSite</span><span class="p">()</span>
<span class="go">None</span>
</pre></div>
</div>
<p>We can also ask for the current component registry (aka site manager
historically); it will return the global one if no current site is set:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.hooks</span> <span class="kn">import</span> <span class="n">getSiteManager</span>
<span class="gp">>>> </span><span class="n">getSiteManager</span><span class="p">()</span>
<span class="go"><BaseGlobalComponents base></span>
</pre></div>
</div>
<p>Let’s set a site now. A site has to be an object that provides the
<tt class="docutils literal"><span class="pre">getSiteManager</span></tt> method, which is specified by
<tt class="docutils literal"><span class="pre">zope.component.interfaces.IPossibleSite</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.interface.registry</span> <span class="kn">import</span> <span class="n">Components</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Site</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="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">registry</span> <span class="o">=</span> <span class="n">Components</span><span class="p">(</span><span class="s">'components'</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">getSiteManager</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="bp">self</span><span class="o">.</span><span class="n">registry</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">zope.component.hooks</span> <span class="kn">import</span> <span class="n">setSite</span>
<span class="gp">>>> </span><span class="n">site1</span> <span class="o">=</span> <span class="n">Site</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">setSite</span><span class="p">(</span><span class="n">site1</span><span class="p">)</span>
</pre></div>
</div>
<p>After this, the newly set site is considered the currently active one:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">getSite</span><span class="p">()</span> <span class="ow">is</span> <span class="n">site1</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">getSiteManager</span><span class="p">()</span> <span class="ow">is</span> <span class="n">site1</span><span class="o">.</span><span class="n">registry</span>
<span class="go">True</span>
</pre></div>
</div>
<p>If we set another site, that one will be considered current:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">site2</span> <span class="o">=</span> <span class="n">Site</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">site2</span><span class="o">.</span><span class="n">registry</span> <span class="ow">is</span> <span class="ow">not</span> <span class="n">site1</span><span class="o">.</span><span class="n">registry</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">setSite</span><span class="p">(</span><span class="n">site2</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">getSite</span><span class="p">()</span> <span class="ow">is</span> <span class="n">site2</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">getSiteManager</span><span class="p">()</span> <span class="ow">is</span> <span class="n">site2</span><span class="o">.</span><span class="n">registry</span>
<span class="go">True</span>
</pre></div>
</div>
<p>Finally we can unset the site and the global component registry is used again:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">setSite</span><span class="p">()</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">getSite</span><span class="p">()</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="n">getSiteManager</span><span class="p">()</span>
<span class="go"><BaseGlobalComponents base></span>
</pre></div>
</div>
<div class="section" id="context-manager">
<h2>Context manager<a class="headerlink" href="#context-manager" title="Permalink to this headline">¶</a></h2>
<p>There also is a context manager for setting the site, which is especially
useful when writing tests:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">zope.component.hooks</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">getSite</span><span class="p">()</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="k">with</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">hooks</span><span class="o">.</span><span class="n">site</span><span class="p">(</span><span class="n">site2</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">getSite</span><span class="p">()</span> <span class="ow">is</span> <span class="n">site2</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">getSite</span><span class="p">()</span>
<span class="go">None</span>
</pre></div>
</div>
<p>The site is properly restored even if the body of the with statement
raises an exception:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">print</span> <span class="n">getSite</span><span class="p">()</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="k">with</span> <span class="n">zope</span><span class="o">.</span><span class="n">component</span><span class="o">.</span><span class="n">hooks</span><span class="o">.</span><span class="n">site</span><span class="p">(</span><span class="n">site2</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">getSite</span><span class="p">()</span> <span class="ow">is</span> <span class="n">site2</span>
<span class="gp">... </span> <span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s">'An error in the body'</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">An error in the body</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">getSite</span><span class="p">()</span>
<span class="go">None</span>
</pre></div>
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