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<?xml version="1.0"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="en"><head><title>Twisted Documentation: The Twisted Plugin System</title><link href="../howto/stylesheet.css" type="text/css" rel="stylesheet" /></head><body bgcolor="white"><h1 class="title">The Twisted Plugin System</h1><div class="toc"><ol><li><a href="#auto0">Writing Extensible Programs</a></li><li><a href="#auto1">Extending an Existing Program</a></li><li><a href="#auto2">Alternate Plugin Packages</a></li><li><a href="#auto3">Plugin Caching</a></li></ol></div><div class="content"><span></span><p>The purpose of this guide is to describe the preferred way to
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="en"><head><title>Twisted Documentation: The Twisted Plugin System</title><link href="../howto/stylesheet.css" type="text/css" rel="stylesheet" /></head><body bgcolor="white"><h1 class="title">The Twisted Plugin System</h1><div class="toc"><ol><li><a href="#auto0">Writing Extensible Programs</a></li><li><a href="#auto1">Extending an Existing Program</a></li><li><a href="#auto2">Alternate Plugin Packages</a></li><li><a href="#auto3">Plugin Caching</a></li><li><a href="#auto4">Further Reading</a></li></ol></div><div class="content"><span></span><p>The purpose of this guide is to describe the preferred way to
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write extensible Twisted applications (and consequently, also to
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describe how to extend applications written in such a way). This
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extensibility is achieved through the definition of one or more
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run, or re-discovered each time the program starts up, or they
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can be polled for repeatedly at runtime (allowing the discovery
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of new plugins installed after the program has started).</li></ul><h2>Writing Extensible Programs<a name="auto0"></a></h2><p>Taking advantage of <code class="API">twisted.plugin</code> is
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a two step process:</p><ol><li>Define an interface which plugins will be required to
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implement. This is done using the <code class="API">zope.interface</code> package in the same way one
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would define an interface for any other purpose.</li><li>At one or more places in your program, invoke <code class="API">twisted.plugin.getPlugins</code> and iterate over
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its result.</li></ol><p>As an example of the first step, consider the following
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interface definition for a physical modelling system.</p><pre class="python">
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a two step process:</p><ol><li><p>
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Define an interface which plugins will be required to implement.
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This is done using the <code class="API">zope.interface</code>
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package in the same way one would define an interface for any other
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A convention for defining interfaces is do so in a file named like
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<em>ProjectName/projectname/iprojectname.py</em>. The rest of this
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document will follow that convention: consider the following
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interface definition be in <code>Matsim/matsim/imatsim.py</code>, an
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interface definition module for a hypothetical material simulation
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At one or more places in your program, invoke <code class="API">twisted.plugin.getPlugins</code> and iterate over its
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As an example of the first step, consider the following interface
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definition for a physical modelling system.
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</p><pre class="python">
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<span class="py-src-keyword">from</span> <span class="py-src-variable">zope</span>.<span class="py-src-variable">interface</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">Interface</span>, <span class="py-src-variable">Attribute</span>
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<span class="py-src-keyword">class</span> <span class="py-src-identifier">IMaterial</span>(<span class="py-src-parameter">Interface</span>):
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<span class="py-src-variable">self</span>.<span class="py-src-variable">dielectricConstant</span> = <span class="py-src-variable">dielectricConstant</span>
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<span class="py-src-keyword">def</span> <span class="py-src-identifier">yieldStress</span>(<span class="py-src-parameter">self</span>, <span class="py-src-parameter">temperature</span>):
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<span class="py-src-keyword">return</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">_yieldStressFactory</span> * <span class="py-src-variable">temperature</span>
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<span class="py-src-keyword">return</span> <span class="py-src-variable">self</span>.<span class="py-src-variable">_yieldStressFactor</span> * <span class="py-src-variable">temperature</span>
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<span class="py-src-variable">steelPlate</span> = <span class="py-src-variable">SimpleMaterial</span>(<span class="py-src-number">2.06842719e11</span>, <span class="py-src-number">2.7</span> + <span class="py-src-number">0.2j</span>)
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<span class="py-src-variable">brassPlate</span> = <span class="py-src-variable">SimpleMaterial</span>(<span class="py-src-number">1.03421359e11</span>, <span class="py-src-number">1.4</span> + <span class="py-src-number">0.5j</span>)
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<span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">plugin</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">IPlugin</span>, <span class="py-src-variable">getPlugin</span>
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<span class="py-src-variable">list</span>(<span class="py-src-variable">getPlugin</span>(<span class="py-src-variable">IPlugin</span>))
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</pre><p>As mentioned, it is normal for exceptions to be raised
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<strong>once</strong> here if plugins have been removed.</p></div><p><a href="../howto/index.html">Index</a></p><span class="version">Version: 2.4.0</span></body></html>
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<strong>once</strong> here if plugins have been removed.</p><h2>Further Reading<a name="auto4"></a></h2><ul><li><a href="components.html">Components: Interfaces and Adapters</a></li></ul></div><p><a href="../howto/index.html">Index</a></p><span class="version">Version: 2.5.0</span></body></html>
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