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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> Filtering and Buffering — Mako 1.1.0 Documentation </title> <!-- begin iterate through site-imported + sphinx environment css_files --> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/changelog.css" type="text/css" /> <link rel="stylesheet" href="_static/sphinx_paramlinks.css" type="text/css" /> <link rel="stylesheet" href="_static/docs.css" type="text/css" /> <!-- end iterate through site-imported + sphinx environment css_files --> <!-- begin layout.mako headers --> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" /> <link rel="top" title="Mako 1.1.0 Documentation" href="index.html" /> <link rel="next" title="The Unicode Chapter" href="unicode.html" /> <link rel="prev" title="Inheritance" href="inheritance.html" /> <!-- end layout.mako headers --> </head> <body> <div id="docs-container"> <div id="docs-header"> <h1>Mako 1.1.0 Documentation</h1> <div id="docs-search"> Search: <form class="search" action="search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Search" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <div id="docs-version-header"> Release: <span class="version-num">1.1.0</span> </div> </div> <div id="docs-top-navigation"> <div id="docs-top-page-control" class="docs-navigation-links"> <ul> <li>Prev: <a href="inheritance.html" title="previous chapter">Inheritance</a> </li> <li>Next: <a href="unicode.html" title="next chapter">The Unicode Chapter</a> </li> <li> <a href="index.html">Table of Contents</a> | <a href="genindex.html">Index</a> </li> </ul> </div> <div id="docs-navigation-banner"> <a href="index.html">Mako 1.1.0 Documentation</a> » Filtering and Buffering <h2> Filtering and Buffering </h2> </div> </div> <div id="docs-body-container"> <div id="docs-sidebar"> <div id="sidebar-banner"> </div> <h3><a href="index.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Filtering and Buffering</a><ul> <li><a class="reference internal" href="#expression-filtering">Expression Filtering</a><ul> <li><a class="reference internal" href="#the-default-filters-argument">The <code class="docutils literal notranslate"><span class="pre">default_filters</span></code> Argument</a></li> <li><a class="reference internal" href="#turning-off-filtering-with-the-n-filter">Turning off Filtering with the <code class="docutils literal notranslate"><span class="pre">n</span></code> Filter</a></li> </ul> </li> <li><a class="reference internal" href="#filtering-defs-and-blocks">Filtering Defs and Blocks</a></li> <li><a class="reference internal" href="#buffering">Buffering</a></li> <li><a class="reference internal" href="#decorating">Decorating</a></li> </ul> </li> </ul> <h4>Previous Topic</h4> <p> <a href="inheritance.html" title="previous chapter">Inheritance</a> </p> <h4>Next Topic</h4> <p> <a href="unicode.html" title="next chapter">The Unicode Chapter</a> </p> <h4>Quick Search</h4> <p> <form class="search" action="search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Search" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </p> </div> <div id="docs-body" class="withsidebar" > <div class="section" id="filtering-and-buffering"> <span id="filtering-toplevel"></span><h1>Filtering and Buffering<a class="headerlink" href="#filtering-and-buffering" title="Permalink to this headline">¶</a></h1> <div class="section" id="expression-filtering"> <span id="id1"></span><h2>Expression Filtering<a class="headerlink" href="#expression-filtering" title="Permalink to this headline">¶</a></h2> <p>As described in the chapter <a class="reference internal" href="syntax.html"><span class="std std-ref">Syntax</span></a>, the “<code class="docutils literal notranslate"><span class="pre">|</span></code>” operator can be applied to a “<code class="docutils literal notranslate"><span class="pre">${}</span></code>” expression to apply escape filters to the output:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="s2">"this is some text"</span> <span class="o">|</span> <span class="n">u</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>The above expression applies URL escaping to the expression, and produces <code class="docutils literal notranslate"><span class="pre">this+is+some+text</span></code>.</p> <p>The built-in escape flags are:</p> <ul> <li><p><code class="docutils literal notranslate"><span class="pre">u</span></code> : URL escaping, provided by <code class="docutils literal notranslate"><span class="pre">urllib.quote_plus(string.encode('utf-8'))</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">h</span></code> : HTML escaping, provided by <code class="docutils literal notranslate"><span class="pre">markupsafe.escape(string)</span></code></p> <div class="versionadded"> <p><span class="versionmodified added">New in version 0.3.4: </span>Prior versions use <code class="docutils literal notranslate"><span class="pre">cgi.escape(string,</span> <span class="pre">True)</span></code>.</p> </div> </li> <li><p><code class="docutils literal notranslate"><span class="pre">x</span></code> : XML escaping</p></li> <li><p><code class="docutils literal notranslate"><span class="pre">trim</span></code> : whitespace trimming, provided by <code class="docutils literal notranslate"><span class="pre">string.strip()</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">entity</span></code> : produces HTML entity references for applicable strings, derived from <code class="docutils literal notranslate"><span class="pre">htmlentitydefs</span></code></p></li> <li><p><code class="docutils literal notranslate"><span class="pre">unicode</span></code> (<code class="docutils literal notranslate"><span class="pre">str</span></code> on Python 3): produces a Python unicode string (this function is applied by default)</p></li> <li><p><code class="docutils literal notranslate"><span class="pre">decode.<some</span> <span class="pre">encoding></span></code>: decode input into a Python unicode with the specified encoding</p></li> <li><p><code class="docutils literal notranslate"><span class="pre">n</span></code> : disable all default filtering; only filters specified in the local expression tag will be applied.</p></li> </ul> <p>To apply more than one filter, separate them by a comma:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="s2">" <tag>some value</tag> "</span> <span class="o">|</span> <span class="n">h</span><span class="p">,</span><span class="n">trim</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>The above produces <code class="docutils literal notranslate"><span class="pre">&lt;tag&gt;some</span> <span class="pre">value&lt;/tag&gt;</span></code>, with no leading or trailing whitespace. The HTML escaping function is applied first, the “trim” function second.</p> <p>Naturally, you can make your own filters too. A filter is just a Python function that accepts a single string argument, and returns the filtered result. The expressions after the <code class="docutils literal notranslate"><span class="pre">|</span></code> operator draw upon the local namespace of the template in which they appear, meaning you can define escaping functions locally:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%!</span> <span class="k">def</span> <span class="nf">myescape</span><span class="p">(</span><span class="n">text</span><span class="p">):</span> <span class="k">return</span> <span class="s2">"<TAG>"</span> <span class="o">+</span> <span class="n">text</span> <span class="o">+</span> <span class="s2">"</TAG>"</span> <span class="cp">%></span><span class="x"></span> <span class="x">Here's some tagged text: </span><span class="cp">${</span><span class="s2">"text"</span> <span class="o">|</span> <span class="n">myescape</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>Or from any Python module:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%!</span> <span class="kn">import</span> <span class="nn">myfilters</span> <span class="cp">%></span><span class="x"></span> <span class="x">Here's some tagged text: </span><span class="cp">${</span><span class="s2">"text"</span> <span class="o">|</span> <span class="n">myfilters</span><span class="o">.</span><span class="n">tagfilter</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>A page can apply a default set of filters to all expression tags using the <code class="docutils literal notranslate"><span class="pre">expression_filter</span></code> argument to the <code class="docutils literal notranslate"><span class="pre">%page</span></code> tag:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%</span><span class="nb">page</span> <span class="na">expression_filter=</span><span class="s">"h"</span><span class="cp">/></span><span class="x"></span> <span class="x">Escaped text: </span><span class="cp">${</span><span class="s2">"<html>some html</html>"</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>Result:</p> <div class="highlight-html notranslate"><div class="highlight"><pre><span></span>Escaped text: <span class="ni">&lt;</span>html<span class="ni">&gt;</span>some html<span class="ni">&lt;</span>/html<span class="ni">&gt;</span></pre></div> </div> <div class="section" id="the-default-filters-argument"> <span id="filtering-default-filters"></span><h3>The <code class="docutils literal notranslate"><span class="pre">default_filters</span></code> Argument<a class="headerlink" href="#the-default-filters-argument" title="Permalink to this headline">¶</a></h3> <p>In addition to the <code class="docutils literal notranslate"><span class="pre">expression_filter</span></code> argument, the <code class="docutils literal notranslate"><span class="pre">default_filters</span></code> argument to both <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code></a> and <a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><code class="xref py py-class docutils literal notranslate"><span class="pre">TemplateLookup</span></code></a> can specify filtering for all expression tags at the programmatic level. This array-based argument, when given its default argument of <code class="docutils literal notranslate"><span class="pre">None</span></code>, will be internally set to <code class="docutils literal notranslate"><span class="pre">["unicode"]</span></code> (or <code class="docutils literal notranslate"><span class="pre">["str"]</span></code> on Python 3), except when <code class="docutils literal notranslate"><span class="pre">disable_unicode=True</span></code> is set in which case it defaults to <code class="docutils literal notranslate"><span class="pre">["str"]</span></code>:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">TemplateLookup</span><span class="p">(</span><span class="n">directories</span><span class="o">=</span><span class="p">[</span><span class="s1">'/tmp'</span><span class="p">],</span> <span class="n">default_filters</span><span class="o">=</span><span class="p">[</span><span class="s1">'unicode'</span><span class="p">])</span></pre></div> </div> <p>To replace the usual <code class="docutils literal notranslate"><span class="pre">unicode</span></code>/<code class="docutils literal notranslate"><span class="pre">str</span></code> function with a specific encoding, the <code class="docutils literal notranslate"><span class="pre">decode</span></code> filter can be substituted:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">TemplateLookup</span><span class="p">(</span><span class="n">directories</span><span class="o">=</span><span class="p">[</span><span class="s1">'/tmp'</span><span class="p">],</span> <span class="n">default_filters</span><span class="o">=</span><span class="p">[</span><span class="s1">'decode.utf8'</span><span class="p">])</span></pre></div> </div> <p>To disable <code class="docutils literal notranslate"><span class="pre">default_filters</span></code> entirely, set it to an empty list:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">TemplateLookup</span><span class="p">(</span><span class="n">directories</span><span class="o">=</span><span class="p">[</span><span class="s1">'/tmp'</span><span class="p">],</span> <span class="n">default_filters</span><span class="o">=</span><span class="p">[])</span></pre></div> </div> <p>Any string name can be added to <code class="docutils literal notranslate"><span class="pre">default_filters</span></code> where it will be added to all expressions as a filter. The filters are applied from left to right, meaning the leftmost filter is applied first.</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">Template</span><span class="p">(</span><span class="n">templatetext</span><span class="p">,</span> <span class="n">default_filters</span><span class="o">=</span><span class="p">[</span><span class="s1">'unicode'</span><span class="p">,</span> <span class="s1">'myfilter'</span><span class="p">])</span></pre></div> </div> <p>To ease the usage of <code class="docutils literal notranslate"><span class="pre">default_filters</span></code> with custom filters, you can also add imports (or other code) to all templates using the <code class="docutils literal notranslate"><span class="pre">imports</span></code> argument:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">TemplateLookup</span><span class="p">(</span><span class="n">directories</span><span class="o">=</span><span class="p">[</span><span class="s1">'/tmp'</span><span class="p">],</span> <span class="n">default_filters</span><span class="o">=</span><span class="p">[</span><span class="s1">'unicode'</span><span class="p">,</span> <span class="s1">'myfilter'</span><span class="p">],</span> <span class="n">imports</span><span class="o">=</span><span class="p">[</span><span class="s1">'from mypackage import myfilter'</span><span class="p">])</span></pre></div> </div> <p>The above will generate templates something like this:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># ....</span> <span class="kn">from</span> <span class="nn">mypackage</span> <span class="kn">import</span> <span class="n">myfilter</span> <span class="k">def</span> <span class="nf">render_body</span><span class="p">(</span><span class="n">context</span><span class="p">):</span> <span class="n">context</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">myfilter</span><span class="p">(</span><span class="nb">unicode</span><span class="p">(</span><span class="s2">"some text"</span><span class="p">)))</span></pre></div> </div> </div> <div class="section" id="turning-off-filtering-with-the-n-filter"> <span id="expression-filtering-nfilter"></span><h3>Turning off Filtering with the <code class="docutils literal notranslate"><span class="pre">n</span></code> Filter<a class="headerlink" href="#turning-off-filtering-with-the-n-filter" title="Permalink to this headline">¶</a></h3> <p>In all cases the special <code class="docutils literal notranslate"><span class="pre">n</span></code> filter, used locally within an expression, will <strong>disable</strong> all filters declared in the <code class="docutils literal notranslate"><span class="pre"><%page></span></code> tag as well as in <code class="docutils literal notranslate"><span class="pre">default_filters</span></code>. Such as:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="s1">'myexpression'</span> <span class="o">|</span> <span class="n">n</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>will render <code class="docutils literal notranslate"><span class="pre">myexpression</span></code> with no filtering of any kind, and:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="s1">'myexpression'</span> <span class="o">|</span> <span class="n">n</span><span class="p">,</span><span class="n">trim</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>will render <code class="docutils literal notranslate"><span class="pre">myexpression</span></code> using the <code class="docutils literal notranslate"><span class="pre">trim</span></code> filter only.</p> <p>Including the <code class="docutils literal notranslate"><span class="pre">n</span></code> filter in a <code class="docutils literal notranslate"><span class="pre"><%page></span></code> tag will only disable <code class="docutils literal notranslate"><span class="pre">default_filters</span></code>. In effect this makes the filters from the tag replace default filters instead of adding to them. For example:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%</span><span class="nb">page</span> <span class="na">expression_filter=</span><span class="s">"n, json.dumps"</span><span class="cp">/></span><span class="x"></span> <span class="x">data = {a: </span><span class="cp">${</span><span class="mi">123</span><span class="cp">}</span><span class="x">, b: </span><span class="cp">${</span><span class="s2">"123"</span><span class="cp">}</span><span class="x">};</span></pre></div> </div> <p>will suppress turning the values into strings using the default filter, so that <code class="docutils literal notranslate"><span class="pre">json.dumps</span></code> (which requires <code class="docutils literal notranslate"><span class="pre">imports=["import</span> <span class="pre">json"]</span></code> or something equivalent) can take the value type into account, formatting numbers as numeric literals and strings as string literals.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 1.0.14: </span>The <code class="docutils literal notranslate"><span class="pre">n</span></code> filter can now be used in the <code class="docutils literal notranslate"><span class="pre"><%page></span></code> tag.</p> </div> </div> </div> <div class="section" id="filtering-defs-and-blocks"> <h2>Filtering Defs and Blocks<a class="headerlink" href="#filtering-defs-and-blocks" title="Permalink to this headline">¶</a></h2> <p>The <code class="docutils literal notranslate"><span class="pre">%def</span></code> and <code class="docutils literal notranslate"><span class="pre">%block</span></code> tags have an argument called <code class="docutils literal notranslate"><span class="pre">filter</span></code> which will apply the given list of filter functions to the output of the <code class="docutils literal notranslate"><span class="pre">%def</span></code>:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"foo()"</span> <span class="na">filter=</span><span class="s">"h, trim"</span><span class="cp">></span><span class="x"></span> <span class="x"> <b>this is bold</b></span> <span class="cp"></%</span><span class="nb">def</span><span class="cp">></span><span class="x"></span></pre></div> </div> <p>When the <code class="docutils literal notranslate"><span class="pre">filter</span></code> attribute is applied to a def as above, the def is automatically <strong>buffered</strong> as well. This is described next.</p> </div> <div class="section" id="buffering"> <h2>Buffering<a class="headerlink" href="#buffering" title="Permalink to this headline">¶</a></h2> <p>One of Mako’s central design goals is speed. To this end, all of the textual content within a template and its various callables is by default piped directly to the single buffer that is stored within the <a class="reference internal" href="runtime.html#mako.runtime.Context" title="mako.runtime.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">Context</span></code></a> object. While this normally is easy to miss, it has certain side effects. The main one is that when you call a def using the normal expression syntax, i.e. <code class="docutils literal notranslate"><span class="pre">${somedef()}</span></code>, it may appear that the return value of the function is the content it produced, which is then delivered to your template just like any other expression substitution, except that normally, this is not the case; the return value of <code class="docutils literal notranslate"><span class="pre">${somedef()}</span></code> is simply the empty string <code class="docutils literal notranslate"><span class="pre">''</span></code>. By the time you receive this empty string, the output of <code class="docutils literal notranslate"><span class="pre">somedef()</span></code> has been sent to the underlying buffer.</p> <p>You may not want this effect, if for example you are doing something like this:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="s2">" results "</span> <span class="o">+</span> <span class="n">somedef</span><span class="p">()</span> <span class="o">+</span> <span class="s2">" more results "</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>If the <code class="docutils literal notranslate"><span class="pre">somedef()</span></code> function produced the content “<code class="docutils literal notranslate"><span class="pre">somedef's</span> <span class="pre">results</span></code>”, the above template would produce this output:</p> <div class="highlight-html notranslate"><div class="highlight"><pre><span></span>somedef's results results more results</pre></div> </div> <p>This is because <code class="docutils literal notranslate"><span class="pre">somedef()</span></code> fully executes before the expression returns the results of its concatenation; the concatenation in turn receives just the empty string as its middle expression.</p> <p>Mako provides two ways to work around this. One is by applying buffering to the <code class="docutils literal notranslate"><span class="pre">%def</span></code> itself:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"somedef()"</span> <span class="na">buffered=</span><span class="s">"True"</span><span class="cp">></span><span class="x"></span> <span class="x"> somedef's results</span> <span class="cp"></%</span><span class="nb">def</span><span class="cp">></span><span class="x"></span></pre></div> </div> <p>The above definition will generate code similar to this:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">somedef</span><span class="p">():</span> <span class="n">context</span><span class="o">.</span><span class="n">push_buffer</span><span class="p">()</span> <span class="k">try</span><span class="p">:</span> <span class="n">context</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"somedef's results"</span><span class="p">)</span> <span class="k">finally</span><span class="p">:</span> <span class="n">buf</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">pop_buffer</span><span class="p">()</span> <span class="k">return</span> <span class="n">buf</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span></pre></div> </div> <p>So that the content of <code class="docutils literal notranslate"><span class="pre">somedef()</span></code> is sent to a second buffer, which is then popped off the stack and its value returned. The speed hit inherent in buffering the output of a def is also apparent.</p> <p>Note that the <code class="docutils literal notranslate"><span class="pre">filter</span></code> argument on <code class="docutils literal notranslate"><span class="pre">%def</span></code> also causes the def to be buffered. This is so that the final content of the <code class="docutils literal notranslate"><span class="pre">%def</span></code> can be delivered to the escaping function in one batch, which reduces method calls and also produces more deterministic behavior for the filtering function itself, which can possibly be useful for a filtering function that wishes to apply a transformation to the text as a whole.</p> <p>The other way to buffer the output of a def or any Mako callable is by using the built-in <code class="docutils literal notranslate"><span class="pre">capture</span></code> function. This function performs an operation similar to the above buffering operation except it is specified by the caller.</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="s2">" results "</span> <span class="o">+</span> <span class="n">capture</span><span class="p">(</span><span class="n">somedef</span><span class="p">)</span> <span class="o">+</span> <span class="s2">" more results "</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>Note that the first argument to the <code class="docutils literal notranslate"><span class="pre">capture</span></code> function is <strong>the function itself</strong>, not the result of calling it. This is because the <code class="docutils literal notranslate"><span class="pre">capture</span></code> function takes over the job of actually calling the target function, after setting up a buffered environment. To send arguments to the function, just send them to <code class="docutils literal notranslate"><span class="pre">capture</span></code> instead:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="n">capture</span><span class="p">(</span><span class="n">somedef</span><span class="p">,</span> <span class="mi">17</span><span class="p">,</span> <span class="s1">'hi'</span><span class="p">,</span> <span class="n">use_paging</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>The above call is equivalent to the unbuffered call:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">${</span><span class="n">somedef</span><span class="p">(</span><span class="mi">17</span><span class="p">,</span> <span class="s1">'hi'</span><span class="p">,</span> <span class="n">use_paging</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span><span class="cp">}</span><span class="x"></span></pre></div> </div> </div> <div class="section" id="decorating"> <h2>Decorating<a class="headerlink" href="#decorating" title="Permalink to this headline">¶</a></h2> <div class="versionadded"> <p><span class="versionmodified added">New in version 0.2.5.</span></p> </div> <p>Somewhat like a filter for a <code class="docutils literal notranslate"><span class="pre">%def</span></code> but more flexible, the <code class="docutils literal notranslate"><span class="pre">decorator</span></code> argument to <code class="docutils literal notranslate"><span class="pre">%def</span></code> allows the creation of a function that will work in a similar manner to a Python decorator. The function can control whether or not the function executes. The original intent of this function is to allow the creation of custom cache logic, but there may be other uses as well.</p> <p><code class="docutils literal notranslate"><span class="pre">decorator</span></code> is intended to be used with a regular Python function, such as one defined in a library module. Here we’ll illustrate the python function defined in the template for simplicities’ sake:</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%!</span> <span class="k">def</span> <span class="nf">bar</span><span class="p">(</span><span class="n">fn</span><span class="p">):</span> <span class="k">def</span> <span class="nf">decorate</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">):</span> <span class="n">context</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"BAR"</span><span class="p">)</span> <span class="n">fn</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">)</span> <span class="n">context</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"BAR"</span><span class="p">)</span> <span class="k">return</span> <span class="s1">''</span> <span class="k">return</span> <span class="n">decorate</span> <span class="cp">%></span><span class="x"></span> <span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"foo()"</span> <span class="na">decorator=</span><span class="s">"bar"</span><span class="cp">></span><span class="x"></span> <span class="x"> this is foo</span> <span class="cp"></%</span><span class="nb">def</span><span class="cp">></span><span class="x"></span> <span class="cp">${</span><span class="n">foo</span><span class="p">()</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>The above template will return, with more whitespace than this, <code class="docutils literal notranslate"><span class="pre">"BAR</span> <span class="pre">this</span> <span class="pre">is</span> <span class="pre">foo</span> <span class="pre">BAR"</span></code>. The function is the render callable itself (or possibly a wrapper around it), and by default will write to the context. To capture its output, use the <a class="reference internal" href="namespaces.html#mako.runtime.capture" title="mako.runtime.capture"><code class="xref py py-func docutils literal notranslate"><span class="pre">capture()</span></code></a> callable in the <code class="docutils literal notranslate"><span class="pre">mako.runtime</span></code> module (available in templates as just <code class="docutils literal notranslate"><span class="pre">runtime</span></code>):</p> <div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%!</span> <span class="k">def</span> <span class="nf">bar</span><span class="p">(</span><span class="n">fn</span><span class="p">):</span> <span class="k">def</span> <span class="nf">decorate</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">):</span> <span class="k">return</span> <span class="s2">"BAR"</span> <span class="o">+</span> <span class="n">runtime</span><span class="o">.</span><span class="n">capture</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="n">fn</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">)</span> <span class="o">+</span> <span class="s2">"BAR"</span> <span class="k">return</span> <span class="n">decorate</span> <span class="cp">%></span><span class="x"></span> <span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"foo()"</span> <span class="na">decorator=</span><span class="s">"bar"</span><span class="cp">></span><span class="x"></span> <span class="x"> this is foo</span> <span class="cp"></%</span><span class="nb">def</span><span class="cp">></span><span class="x"></span> <span class="cp">${</span><span class="n">foo</span><span class="p">()</span><span class="cp">}</span><span class="x"></span></pre></div> </div> <p>The decorator can be used with top-level defs as well as nested defs, and blocks too. Note that when calling a top-level def from the <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code></a> API, i.e. <code class="docutils literal notranslate"><span class="pre">template.get_def('somedef').render()</span></code>, the decorator has to write the output to the <code class="docutils literal notranslate"><span class="pre">context</span></code>, i.e. as in the first example. The return value gets discarded.</p> </div> </div> </div> </div> <div id="docs-bottom-navigation" class="docs-navigation-links"> Previous: <a href="inheritance.html" title="previous chapter">Inheritance</a> Next: <a href="unicode.html" title="next chapter">The Unicode Chapter</a> <div id="docs-copyright"> © Copyright the Mako authors and contributors. 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