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<title>Write your own filter &mdash; Pygments</title>
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</head>
<body>
<div id="content">
<h1 class="heading">Pygments</h1>
<h2 class="subheading">Write your own filter</h2>
<a id="backlink" href="index.html">&laquo; Back To Index</a>
<div class="toc">
<h2>Contents</h2>
<ul class="contents">
<li><a href="#subclassing-filters">Subclassing Filters</a></li>
<li><a href="#using-a-decorator">Using a decorator</a></li>
</ul>
</div>
<!-- -*- mode: rst -*- -->
<p><em>New in Pygments 0.7.</em></p>
<p>Writing own filters is very easy. All you have to do is to subclass
the <cite>Filter</cite> class and override the <cite>filter</cite> method. Additionally a
filter is instanciated with some keyword arguments you can use to
adjust the behavior of your filter.</p>
<div class="section" id="subclassing-filters">
<h3>Subclassing Filters</h3>
<p>As an example, we write a filter that converts all <cite>Name.Function</cite> tokens
to normal <cite>Name</cite> tokens to make the output less colorful.</p>
<div class="syntax"><pre><span class="kn">from</span> <span class="nn">pygments.util</span> <span class="kn">import</span> <span class="n">get_bool_opt</span>
<span class="kn">from</span> <span class="nn">pygments.token</span> <span class="kn">import</span> <span class="n">Name</span>
<span class="kn">from</span> <span class="nn">pygments.filter</span> <span class="kn">import</span> <span class="n">Filter</span>
<span class="k">class</span> <span class="nc">UncolorFilter</span><span class="p">(</span><span class="n">Filter</span><span class="p">):</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="o">**</span><span class="n">options</span><span class="p">):</span>
<span class="n">Filter</span><span class="o">.</span><span class="n">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">**</span><span class="n">options</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">class_too</span> <span class="o">=</span> <span class="n">get_bool_opt</span><span class="p">(</span><span class="n">options</span><span class="p">,</span> <span class="s">&#39;classtoo&#39;</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">filter</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">lexer</span><span class="p">,</span> <span class="n">stream</span><span class="p">):</span>
<span class="k">for</span> <span class="n">ttype</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">stream</span><span class="p">:</span>
<span class="k">if</span> <span class="n">ttype</span> <span class="ow">is</span> <span class="n">Name</span><span class="o">.</span><span class="n">Function</span> <span class="ow">or</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">class_too</span> <span class="ow">and</span>
<span class="n">ttype</span> <span class="ow">is</span> <span class="n">Name</span><span class="o">.</span><span class="n">Class</span><span class="p">):</span>
<span class="n">ttype</span> <span class="o">=</span> <span class="n">Name</span>
<span class="k">yield</span> <span class="n">ttype</span><span class="p">,</span> <span class="n">value</span>
</pre></div>
<p>Some notes on the <cite>lexer</cite> argument: that can be quite confusing since it doesn't
need to be a lexer instance. If a filter was added by using the <cite>add_filter()</cite>
function of lexers, that lexer is registered for the filter. In that case
<cite>lexer</cite> will refer to the lexer that has registered the filter. It <em>can</em> be used
to access options passed to a lexer. Because it could be <cite>None</cite> you always have
to check for that case if you access it.</p>
</div>
<div class="section" id="using-a-decorator">
<h3>Using a decorator</h3>
<p>You can also use the <cite>simplefilter</cite> decorator from the <cite>pygments.filter</cite> module:</p>
<div class="syntax"><pre><span class="kn">from</span> <span class="nn">pygments.util</span> <span class="kn">import</span> <span class="n">get_bool_opt</span>
<span class="kn">from</span> <span class="nn">pygments.token</span> <span class="kn">import</span> <span class="n">Name</span>
<span class="kn">from</span> <span class="nn">pygments.filter</span> <span class="kn">import</span> <span class="n">simplefilter</span>
<span class="nd">@simplefilter</span>
<span class="k">def</span> <span class="nf">uncolor</span><span class="p">(</span><span class="n">lexer</span><span class="p">,</span> <span class="n">stream</span><span class="p">,</span> <span class="n">options</span><span class="p">):</span>
<span class="n">class_too</span> <span class="o">=</span> <span class="n">get_bool_opt</span><span class="p">(</span><span class="n">options</span><span class="p">,</span> <span class="s">&#39;classtoo&#39;</span><span class="p">)</span>
<span class="k">for</span> <span class="n">ttype</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">stream</span><span class="p">:</span>
<span class="k">if</span> <span class="n">ttype</span> <span class="ow">is</span> <span class="n">Name</span><span class="o">.</span><span class="n">Function</span> <span class="ow">or</span> <span class="p">(</span><span class="n">class_too</span> <span class="ow">and</span>
<span class="n">ttype</span> <span class="ow">is</span> <span class="n">Name</span><span class="o">.</span><span class="n">Class</span><span class="p">):</span>
<span class="n">ttype</span> <span class="o">=</span> <span class="n">Name</span>
<span class="k">yield</span> <span class="n">ttype</span><span class="p">,</span> <span class="n">value</span>
</pre></div>
<p>The decorator automatically subclasses an internal filter class and uses the
decorated function for filtering.</p>
</div>
</div>
</body>
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