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Mako 1.1.0 Documentation
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<h1>Mako 1.1.0 Documentation</h1>
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Inheritance
<h2>
Inheritance
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<h3><a href="index.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Inheritance</a><ul>
<li><a class="reference internal" href="#nesting-blocks">Nesting Blocks</a></li>
<li><a class="reference internal" href="#rendering-a-named-block-multiple-times">Rendering a Named Block Multiple Times</a></li>
<li><a class="reference internal" href="#but-what-about-defs">But what about Defs?</a></li>
<li><a class="reference internal" href="#using-the-next-namespace-to-produce-content-wrapping">Using the <code class="docutils literal notranslate"><span class="pre">next</span></code> Namespace to Produce Content Wrapping</a></li>
<li><a class="reference internal" href="#using-the-parent-namespace-to-augment-defs">Using the <code class="docutils literal notranslate"><span class="pre">parent</span></code> Namespace to Augment Defs</a></li>
<li><a class="reference internal" href="#using-include-with-template-inheritance">Using <code class="docutils literal notranslate"><span class="pre"><%include></span></code> with Template Inheritance</a></li>
<li><a class="reference internal" href="#inheritable-attributes">Inheritable Attributes</a></li>
</ul>
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<div class="section" id="inheritance">
<span id="inheritance-toplevel"></span><h1>Inheritance<a class="headerlink" href="#inheritance" title="Permalink to this headline">¶</a></h1>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Most of the inheritance examples here take advantage of a feature that’s
new in Mako as of version 0.4.1 called the “block”. This tag is very similar to
the “def” tag but is more streamlined for usage with inheritance. Note that
all of the examples here which use blocks can also use defs instead. Contrasting
usages will be illustrated.</p>
</div>
<p>Using template inheritance, two or more templates can organize
themselves into an <strong>inheritance chain</strong>, where content and
functions from all involved templates can be intermixed. The
general paradigm of template inheritance is this: if a template
<code class="docutils literal notranslate"><span class="pre">A</span></code> inherits from template <code class="docutils literal notranslate"><span class="pre">B</span></code>, then template <code class="docutils literal notranslate"><span class="pre">A</span></code> agrees
to send the executional control to template <code class="docutils literal notranslate"><span class="pre">B</span></code> at runtime
(<code class="docutils literal notranslate"><span class="pre">A</span></code> is called the <strong>inheriting</strong> template). Template <code class="docutils literal notranslate"><span class="pre">B</span></code>,
the <strong>inherited</strong> template, then makes decisions as to what
resources from <code class="docutils literal notranslate"><span class="pre">A</span></code> shall be executed.</p>
<p>In practice, it looks like this. Here’s a hypothetical inheriting
template, <code class="docutils literal notranslate"><span class="pre">index.html</span></code>:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## index.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.html"</span><span class="cp">/></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is some header content</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x">this is the body content.</span></pre></div>
</div>
<p>And <code class="docutils literal notranslate"><span class="pre">base.html</span></code>, the inherited template:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## base.html</span><span class="x"></span>
<span class="x"><html></span>
<span class="x"> <body></span>
<span class="x"> <div class="header"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">/></span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> <div class="footer"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"footer"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is the footer</span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </body></span>
<span class="x"></html></span></pre></div>
</div>
<p>Here is a breakdown of the execution:</p>
<ol class="arabic">
<li><p>When <code class="docutils literal notranslate"><span class="pre">index.html</span></code> is rendered, control immediately passes to
<code class="docutils literal notranslate"><span class="pre">base.html</span></code>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">base.html</span></code> then renders the top part of an HTML document,
then invokes the <code class="docutils literal notranslate"><span class="pre"><%block</span> <span class="pre">name="header"></span></code> block. It invokes the
underlying <code class="docutils literal notranslate"><span class="pre">header()</span></code> function off of a built-in namespace
called <code class="docutils literal notranslate"><span class="pre">self</span></code> (this namespace was first introduced in the
<a class="reference internal" href="namespaces.html"><span class="doc">Namespaces chapter</span></a> in <a class="reference internal" href="namespaces.html#namespace-self"><span class="std std-ref">self</span></a>). Since
<code class="docutils literal notranslate"><span class="pre">index.html</span></code> is the topmost template and also defines a block
called <code class="docutils literal notranslate"><span class="pre">header</span></code>, it’s this <code class="docutils literal notranslate"><span class="pre">header</span></code> block that ultimately gets
executed – instead of the one that’s present in <code class="docutils literal notranslate"><span class="pre">base.html</span></code>.</p></li>
<li><p>Control comes back to <code class="docutils literal notranslate"><span class="pre">base.html</span></code>. Some more HTML is
rendered.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">base.html</span></code> executes <code class="docutils literal notranslate"><span class="pre">self.body()</span></code>. The <code class="docutils literal notranslate"><span class="pre">body()</span></code>
function on all template-based namespaces refers to the main
body of the template, therefore the main body of
<code class="docutils literal notranslate"><span class="pre">index.html</span></code> is rendered.</p></li>
<li><p>When <code class="docutils literal notranslate"><span class="pre"><%block</span> <span class="pre">name="header"></span></code> is encountered in <code class="docutils literal notranslate"><span class="pre">index.html</span></code>
during the <code class="docutils literal notranslate"><span class="pre">self.body()</span></code> call, a conditional is checked – does the
current inherited template, i.e. <code class="docutils literal notranslate"><span class="pre">base.html</span></code>, also define this block? If yes,
the <code class="docutils literal notranslate"><span class="pre"><%block></span></code> is <strong>not</strong> executed here – the inheritance
mechanism knows that the parent template is responsible for rendering
this block (and in fact it already has). In other words a block
only renders in its <em>basemost scope</em>.</p></li>
<li><p>Control comes back to <code class="docutils literal notranslate"><span class="pre">base.html</span></code>. More HTML is rendered,
then the <code class="docutils literal notranslate"><span class="pre"><%block</span> <span class="pre">name="footer"></span></code> expression is invoked.</p></li>
<li><p>The <code class="docutils literal notranslate"><span class="pre">footer</span></code> block is only defined in <code class="docutils literal notranslate"><span class="pre">base.html</span></code>, so being
the topmost definition of <code class="docutils literal notranslate"><span class="pre">footer</span></code>, it’s the one that
executes. If <code class="docutils literal notranslate"><span class="pre">index.html</span></code> also specified <code class="docutils literal notranslate"><span class="pre">footer</span></code>, then
its version would <strong>override</strong> that of the base.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">base.html</span></code> finishes up rendering its HTML and the template
is complete, producing:</p>
<div class="highlight-html notranslate"><div class="highlight"><pre><span></span><span class="p"><</span><span class="nt">html</span><span class="p">></span>
<span class="p"><</span><span class="nt">body</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"header"</span><span class="p">></span>
this is some header content
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
this is the body content.
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"footer"</span><span class="p">></span>
this is the footer
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"></</span><span class="nt">body</span><span class="p">></span>
<span class="p"></</span><span class="nt">html</span><span class="p">></span></pre></div>
</div>
</li>
</ol>
<p>…and that is template inheritance in a nutshell. The main idea
is that the methods that you call upon <code class="docutils literal notranslate"><span class="pre">self</span></code> always
correspond to the topmost definition of that method. Very much
the way <code class="docutils literal notranslate"><span class="pre">self</span></code> works in a Python class, even though Mako is
not actually using Python class inheritance to implement this
functionality. (Mako doesn’t take the “inheritance” metaphor too
seriously; while useful to setup some commonly recognized
semantics, a textual template is not very much like an
object-oriented class construct in practice).</p>
<div class="section" id="nesting-blocks">
<h2>Nesting Blocks<a class="headerlink" href="#nesting-blocks" title="Permalink to this headline">¶</a></h2>
<p>The named blocks defined in an inherited template can also be nested within
other blocks. The name given to each block is globally accessible via any inheriting
template. We can add a new block <code class="docutils literal notranslate"><span class="pre">title</span></code> to our <code class="docutils literal notranslate"><span class="pre">header</span></code> block:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## base.html</span><span class="x"></span>
<span class="x"><html></span>
<span class="x"> <body></span>
<span class="x"> <div class="header"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> <h2></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"title"</span><span class="cp">/></span><span class="x"></span>
<span class="x"> </h2></span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> <div class="footer"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"footer"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is the footer</span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </body></span>
<span class="x"></html></span></pre></div>
</div>
<p>The inheriting template can name either or both of <code class="docutils literal notranslate"><span class="pre">header</span></code> and <code class="docutils literal notranslate"><span class="pre">title</span></code>, separately
or nested themselves:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## index.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.html"</span><span class="cp">/></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is some header content</span>
<span class="x"> </span><span class="cp">${</span><span class="n">parent</span><span class="o">.</span><span class="n">header</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"title"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is the title</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x">this is the body content.</span></pre></div>
</div>
<p>Note when we overrode <code class="docutils literal notranslate"><span class="pre">header</span></code>, we added an extra call <code class="docutils literal notranslate"><span class="pre">${parent.header()}</span></code> in order to invoke
the parent’s <code class="docutils literal notranslate"><span class="pre">header</span></code> block in addition to our own. That’s described in more detail below,
in <a class="reference internal" href="#parent-namespace"><span class="std std-ref">Using the parent Namespace to Augment Defs</span></a>.</p>
</div>
<div class="section" id="rendering-a-named-block-multiple-times">
<h2>Rendering a Named Block Multiple Times<a class="headerlink" href="#rendering-a-named-block-multiple-times" title="Permalink to this headline">¶</a></h2>
<p>Recall from the section <a class="reference internal" href="defs.html#blocks"><span class="std std-ref">Using Blocks</span></a> that a named block is just like a <code class="docutils literal notranslate"><span class="pre"><%def></span></code>,
with some different usage rules. We can call one of our named sections distinctly, for example
a section that is used more than once, such as the title of a page:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="x"><html></span>
<span class="x"> <head></span>
<span class="x"> <title></span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">title</span><span class="p">()</span><span class="cp">}</span><span class="x"></title></span>
<span class="x"> </head></span>
<span class="x"> <body></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> <h2></span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"title"</span><span class="cp">/></span><span class="x"></h2></span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> </body></span>
<span class="x"></html></span></pre></div>
</div>
<p>Where above an inheriting template can define <code class="docutils literal notranslate"><span class="pre"><%block</span> <span class="pre">name="title"></span></code> just once, and it will be
used in the base template both in the <code class="docutils literal notranslate"><span class="pre"><title></span></code> section as well as the <code class="docutils literal notranslate"><span class="pre"><h2></span></code>.</p>
</div>
<div class="section" id="but-what-about-defs">
<h2>But what about Defs?<a class="headerlink" href="#but-what-about-defs" title="Permalink to this headline">¶</a></h2>
<p>The previous example used the <code class="docutils literal notranslate"><span class="pre"><%block></span></code> tag to produce areas of content
to be overridden. Before Mako 0.4.1, there wasn’t any such tag – instead
there was only the <code class="docutils literal notranslate"><span class="pre"><%def></span></code> tag. As it turns out, named blocks and defs are
largely interchangeable. The def simply doesn’t call itself automatically,
and has more open-ended naming and scoping rules that are more flexible and similar
to Python itself, but less suited towards layout. The first example from
this chapter using defs would look like:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## index.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.html"</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">"header()"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is some header content</span>
<span class="cp"></%</span><span class="nb">def</span><span class="cp">></span><span class="x"></span>
<span class="x">this is the body content.</span></pre></div>
</div>
<p>And <code class="docutils literal notranslate"><span class="pre">base.html</span></code>, the inherited template:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## base.html</span><span class="x"></span>
<span class="x"><html></span>
<span class="x"> <body></span>
<span class="x"> <div class="header"></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">header</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> <div class="footer"></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">footer</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </body></span>
<span class="x"></html></span>
<span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"header()"</span><span class="cp">/></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"footer()"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is the footer</span>
<span class="cp"></%</span><span class="nb">def</span><span class="cp">></span><span class="x"></span></pre></div>
</div>
<p>Above, we illustrate that defs differ from blocks in that their definition
and invocation are defined in two separate places, instead of at once. You can <em>almost</em> do exactly what a
block does if you put the two together:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="x"><div class="header"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"header()"</span><span class="cp">></%</span><span class="nb">def</span><span class="cp">>${</span><span class="bp">self</span><span class="o">.</span><span class="n">header</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"></div></span></pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre"><%block></span></code> is obviously more streamlined than the <code class="docutils literal notranslate"><span class="pre"><%def></span></code> for this kind
of usage. In addition,
the above “inline” approach with <code class="docutils literal notranslate"><span class="pre"><%def></span></code> does not work with nesting:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="x"><head></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"header()"</span><span class="cp">></span><span class="x"></span>
<span class="x"> <title></span>
<span class="x"> ## this won't work !</span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"title()"</span><span class="cp">></span><span class="x">default title</span><span class="cp"></%</span><span class="nb">def</span><span class="cp">>${</span><span class="bp">self</span><span class="o">.</span><span class="n">title</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> </title></span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">def</span><span class="cp">>${</span><span class="bp">self</span><span class="o">.</span><span class="n">header</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"></head></span></pre></div>
</div>
<p>Where above, the <code class="docutils literal notranslate"><span class="pre">title()</span></code> def, because it’s a def within a def, is not part of the
template’s exported namespace and will not be part of <code class="docutils literal notranslate"><span class="pre">self</span></code>. If the inherited template
did define its own <code class="docutils literal notranslate"><span class="pre">title</span></code> def at the top level, it would be called, but the “default title”
above is not present at all on <code class="docutils literal notranslate"><span class="pre">self</span></code> no matter what. For this to work as expected
you’d instead need to say:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="x"><head></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"header()"</span><span class="cp">></span><span class="x"></span>
<span class="x"> <title></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">title</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> </title></span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">def</span><span class="cp">>${</span><span class="bp">self</span><span class="o">.</span><span class="n">header</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">def</span> <span class="na">name=</span><span class="s">"title()"</span><span class="cp">/></span><span class="x"></span>
<span class="x"></head></span></pre></div>
</div>
<p>That is, <code class="docutils literal notranslate"><span class="pre">title</span></code> is defined outside of any other defs so that it is in the <code class="docutils literal notranslate"><span class="pre">self</span></code> namespace.
It works, but the definition needs to be potentially far away from the point of render.</p>
<p>A named block is always placed in the <code class="docutils literal notranslate"><span class="pre">self</span></code> namespace, regardless of nesting,
so this restriction is lifted:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## base.html</span><span class="x"></span>
<span class="x"><head></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> <title></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"title"</span><span class="cp">/></span><span class="x"></span>
<span class="x"> </title></span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"></head></span></pre></div>
</div>
<p>The above template defines <code class="docutils literal notranslate"><span class="pre">title</span></code> inside of <code class="docutils literal notranslate"><span class="pre">header</span></code>, and an inheriting template can define
one or both in <strong>any</strong> configuration, nested inside each other or not, in order for them to be used:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## index.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.html"</span><span class="cp">/></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"title"</span><span class="cp">></span><span class="x"></span>
<span class="x"> the title</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> the header</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span></pre></div>
</div>
<p>So while the <code class="docutils literal notranslate"><span class="pre"><%block></span></code> tag lifts the restriction of nested blocks not being available externally,
in order to achieve this it <em>adds</em> the restriction that all block names in a single template need
to be globally unique within the template, and additionally that a <code class="docutils literal notranslate"><span class="pre"><%block></span></code> can’t be defined
inside of a <code class="docutils literal notranslate"><span class="pre"><%def></span></code>. It’s a more restricted tag suited towards a more specific use case than <code class="docutils literal notranslate"><span class="pre"><%def></span></code>.</p>
</div>
<div class="section" id="using-the-next-namespace-to-produce-content-wrapping">
<h2>Using the <code class="docutils literal notranslate"><span class="pre">next</span></code> Namespace to Produce Content Wrapping<a class="headerlink" href="#using-the-next-namespace-to-produce-content-wrapping" title="Permalink to this headline">¶</a></h2>
<p>Sometimes you have an inheritance chain that spans more than two
templates. Or maybe you don’t, but you’d like to build your
system such that extra inherited templates can be inserted in
the middle of a chain where they would be smoothly integrated.
If each template wants to define its layout just within its main
body, you can’t just call <code class="docutils literal notranslate"><span class="pre">self.body()</span></code> to get at the
inheriting template’s body, since that is only the topmost body.
To get at the body of the <em>next</em> template, you call upon the
namespace <code class="docutils literal notranslate"><span class="pre">next</span></code>, which is the namespace of the template
<strong>immediately following</strong> the current template.</p>
<p>Lets change the line in <code class="docutils literal notranslate"><span class="pre">base.html</span></code> which calls upon
<code class="docutils literal notranslate"><span class="pre">self.body()</span></code> to instead call upon <code class="docutils literal notranslate"><span class="pre">next.body()</span></code>:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## base.html</span><span class="x"></span>
<span class="x"><html></span>
<span class="x"> <body></span>
<span class="x"> <div class="header"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">/></span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </span><span class="cp">${</span><span class="nb">next</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> <div class="footer"></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"footer"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is the footer</span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"> </div></span>
<span class="x"> </body></span>
<span class="x"></html></span></pre></div>
</div>
<p>Lets also add an intermediate template called <code class="docutils literal notranslate"><span class="pre">layout.html</span></code>,
which inherits from <code class="docutils literal notranslate"><span class="pre">base.html</span></code>:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## layout.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.html"</span><span class="cp">/></span><span class="x"></span>
<span class="x"><ul></span>
<span class="x"> </span><span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"toolbar"</span><span class="cp">></span><span class="x"></span>
<span class="x"> <li>selection 1</li></span>
<span class="x"> <li>selection 2</li></span>
<span class="x"> <li>selection 3</li></span>
<span class="x"> </span><span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x"></ul></span>
<span class="x"><div class="mainlayout"></span>
<span class="x"> </span><span class="cp">${</span><span class="nb">next</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"></div></span></pre></div>
</div>
<p>And finally change <code class="docutils literal notranslate"><span class="pre">index.html</span></code> to inherit from
<code class="docutils literal notranslate"><span class="pre">layout.html</span></code> instead:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## index.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"layout.html"</span><span class="cp">/></span>
<span class="cp">## .. rest of template</span><span class="x"></span></pre></div>
</div>
<p>In this setup, each call to <code class="docutils literal notranslate"><span class="pre">next.body()</span></code> will render the body
of the next template in the inheritance chain (which can be
written as <code class="docutils literal notranslate"><span class="pre">base.html</span> <span class="pre">-></span> <span class="pre">layout.html</span> <span class="pre">-></span> <span class="pre">index.html</span></code>). Control
is still first passed to the bottommost template <code class="docutils literal notranslate"><span class="pre">base.html</span></code>,
and <code class="docutils literal notranslate"><span class="pre">self</span></code> still references the topmost definition of any
particular def.</p>
<p>The output we get would be:</p>
<div class="highlight-html notranslate"><div class="highlight"><pre><span></span><span class="p"><</span><span class="nt">html</span><span class="p">></span>
<span class="p"><</span><span class="nt">body</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"header"</span><span class="p">></span>
this is some header content
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"><</span><span class="nt">ul</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 1<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 2<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 3<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"></</span><span class="nt">ul</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"mainlayout"</span><span class="p">></span>
this is the body content.
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"footer"</span><span class="p">></span>
this is the footer
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"></</span><span class="nt">body</span><span class="p">></span>
<span class="p"></</span><span class="nt">html</span><span class="p">></span></pre></div>
</div>
<p>So above, we have the <code class="docutils literal notranslate"><span class="pre"><html></span></code>, <code class="docutils literal notranslate"><span class="pre"><body></span></code> and
<code class="docutils literal notranslate"><span class="pre">header</span></code>/<code class="docutils literal notranslate"><span class="pre">footer</span></code> layout of <code class="docutils literal notranslate"><span class="pre">base.html</span></code>, we have the
<code class="docutils literal notranslate"><span class="pre"><ul></span></code> and <code class="docutils literal notranslate"><span class="pre">mainlayout</span></code> section of <code class="docutils literal notranslate"><span class="pre">layout.html</span></code>, and the
main body of <code class="docutils literal notranslate"><span class="pre">index.html</span></code> as well as its overridden <code class="docutils literal notranslate"><span class="pre">header</span></code>
def. The <code class="docutils literal notranslate"><span class="pre">layout.html</span></code> template is inserted into the middle of
the chain without <code class="docutils literal notranslate"><span class="pre">base.html</span></code> having to change anything.
Without the <code class="docutils literal notranslate"><span class="pre">next</span></code> namespace, only the main body of
<code class="docutils literal notranslate"><span class="pre">index.html</span></code> could be used; there would be no way to call
<code class="docutils literal notranslate"><span class="pre">layout.html</span></code>’s body content.</p>
</div>
<div class="section" id="using-the-parent-namespace-to-augment-defs">
<span id="parent-namespace"></span><h2>Using the <code class="docutils literal notranslate"><span class="pre">parent</span></code> Namespace to Augment Defs<a class="headerlink" href="#using-the-parent-namespace-to-augment-defs" title="Permalink to this headline">¶</a></h2>
<p>Lets now look at the other inheritance-specific namespace, the
opposite of <code class="docutils literal notranslate"><span class="pre">next</span></code> called <code class="docutils literal notranslate"><span class="pre">parent</span></code>. <code class="docutils literal notranslate"><span class="pre">parent</span></code> is the
namespace of the template <strong>immediately preceding</strong> the current
template. What’s useful about this namespace is that
defs or blocks can call upon their overridden versions.
This is not as hard as it sounds and
is very much like using the <code class="docutils literal notranslate"><span class="pre">super</span></code> keyword in Python. Lets
modify <code class="docutils literal notranslate"><span class="pre">index.html</span></code> to augment the list of selections provided
by the <code class="docutils literal notranslate"><span class="pre">toolbar</span></code> function in <code class="docutils literal notranslate"><span class="pre">layout.html</span></code>:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## index.html</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"layout.html"</span><span class="cp">/></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> this is some header content</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"toolbar"</span><span class="cp">></span>
<span class="cp">## call the parent's toolbar first</span><span class="x"></span>
<span class="x"> </span><span class="cp">${</span><span class="n">parent</span><span class="o">.</span><span class="n">toolbar</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"> <li>selection 4</li></span>
<span class="x"> <li>selection 5</li></span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span>
<span class="x">this is the body content.</span></pre></div>
</div>
<p>Above, we implemented a <code class="docutils literal notranslate"><span class="pre">toolbar()</span></code> function, which is meant
to override the definition of <code class="docutils literal notranslate"><span class="pre">toolbar</span></code> within the inherited
template <code class="docutils literal notranslate"><span class="pre">layout.html</span></code>. However, since we want the content
from that of <code class="docutils literal notranslate"><span class="pre">layout.html</span></code> as well, we call it via the
<code class="docutils literal notranslate"><span class="pre">parent</span></code> namespace whenever we want it’s content, in this case
before we add our own selections. So the output for the whole
thing is now:</p>
<div class="highlight-html notranslate"><div class="highlight"><pre><span></span><span class="p"><</span><span class="nt">html</span><span class="p">></span>
<span class="p"><</span><span class="nt">body</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"header"</span><span class="p">></span>
this is some header content
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"><</span><span class="nt">ul</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 1<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 2<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 3<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 4<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"><</span><span class="nt">li</span><span class="p">></span>selection 5<span class="p"></</span><span class="nt">li</span><span class="p">></span>
<span class="p"></</span><span class="nt">ul</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"mainlayout"</span><span class="p">></span>
this is the body content.
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"footer"</span><span class="p">></span>
this is the footer
<span class="p"></</span><span class="nt">div</span><span class="p">></span>
<span class="p"></</span><span class="nt">body</span><span class="p">></span>
<span class="p"></</span><span class="nt">html</span><span class="p">></span></pre></div>
</div>
<p>and you’re now a template inheritance ninja!</p>
</div>
<div class="section" id="using-include-with-template-inheritance">
<h2>Using <code class="docutils literal notranslate"><span class="pre"><%include></span></code> with Template Inheritance<a class="headerlink" href="#using-include-with-template-inheritance" title="Permalink to this headline">¶</a></h2>
<p>A common source of confusion is the behavior of the <code class="docutils literal notranslate"><span class="pre"><%include></span></code> tag,
often in conjunction with its interaction within template inheritance.
Key to understanding the <code class="docutils literal notranslate"><span class="pre"><%include></span></code> tag is that it is a <em>dynamic</em>, e.g.
runtime, include, and not a static include. The <code class="docutils literal notranslate"><span class="pre"><%include></span></code> is only processed
as the template renders, and not at inheritance setup time. When encountered,
the referenced template is run fully as an entirely separate template with no
linkage to any current inheritance structure.</p>
<p>If the tag were on the other hand a <em>static</em> include, this would allow source
within the included template to interact within the same inheritance context
as the calling template, but currently Mako has no static include facility.</p>
<p>In practice, this means that <code class="docutils literal notranslate"><span class="pre"><%block></span></code> elements defined in an <code class="docutils literal notranslate"><span class="pre"><%include></span></code>
file will not interact with corresponding <code class="docutils literal notranslate"><span class="pre"><%block></span></code> elements in the calling
template.</p>
<p>A common mistake is along these lines:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## partials.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> Global Header</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span>
<span class="cp">## parent.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">include</span> <span class="na">file=</span><span class="s">"partials.mako"</span><span class="cp">></span>
<span class="cp">## child.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"parent.mako"</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> Custom Header</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span></pre></div>
</div>
<p>Above, one might expect that the <code class="docutils literal notranslate"><span class="pre">"header"</span></code> block declared in <code class="docutils literal notranslate"><span class="pre">child.mako</span></code>
might be invoked, as a result of it overriding the same block present in
<code class="docutils literal notranslate"><span class="pre">parent.mako</span></code> via the include for <code class="docutils literal notranslate"><span class="pre">partials.mako</span></code>. But this is not the case.
Instead, <code class="docutils literal notranslate"><span class="pre">parent.mako</span></code> will invoke <code class="docutils literal notranslate"><span class="pre">partials.mako</span></code>, which then invokes
<code class="docutils literal notranslate"><span class="pre">"header"</span></code> in <code class="docutils literal notranslate"><span class="pre">partials.mako</span></code>, and then is finished rendering. Nothing
from <code class="docutils literal notranslate"><span class="pre">child.mako</span></code> will render; there is no interaction between the <code class="docutils literal notranslate"><span class="pre">"header"</span></code>
block in <code class="docutils literal notranslate"><span class="pre">child.mako</span></code> and the <code class="docutils literal notranslate"><span class="pre">"header"</span></code> block in <code class="docutils literal notranslate"><span class="pre">partials.mako</span></code>.</p>
<p>Instead, <code class="docutils literal notranslate"><span class="pre">parent.mako</span></code> must explicitly state the inheritance structure.
In order to call upon specific elements of <code class="docutils literal notranslate"><span class="pre">partials.mako</span></code>, we will call upon
it as a namespace:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## partials.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> Global Header</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span>
<span class="cp">## parent.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">namespace</span> <span class="na">name=</span><span class="s">"partials"</span> <span class="na">file=</span><span class="s">"partials.mako"</span><span class="cp">/></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> </span><span class="cp">${</span><span class="n">partials</span><span class="o">.</span><span class="n">header</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span>
<span class="cp">## child.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"parent.mako"</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"header"</span><span class="cp">></span><span class="x"></span>
<span class="x"> Custom Header</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span></pre></div>
</div>
<p>Where above, <code class="docutils literal notranslate"><span class="pre">parent.mako</span></code> states the inheritance structure that <code class="docutils literal notranslate"><span class="pre">child.mako</span></code>
is to participate within. <code class="docutils literal notranslate"><span class="pre">partials.mako</span></code> only defines defs/blocks that can be
used on a per-name basis.</p>
<p>Another scenario is below, which results in both <code class="docutils literal notranslate"><span class="pre">"SectionA"</span></code> blocks being rendered for the <code class="docutils literal notranslate"><span class="pre">child.mako</span></code> document:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## base.mako</span><span class="x"></span>
<span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"SectionA"</span><span class="cp">></span><span class="x"></span>
<span class="x"> base.mako</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span>
<span class="cp">## parent.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.mako"</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">include</span> <span class="na">file=</span><span class="s">"child.mako"</span><span class="cp">></span>
<span class="cp">## child.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"SectionA"</span><span class="cp">></span><span class="x"></span>
<span class="x"> child.mako</span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span></pre></div>
</div>
<p>The resolution is similar; instead of using <code class="docutils literal notranslate"><span class="pre"><%include></span></code>, we call upon the blocks
of <code class="docutils literal notranslate"><span class="pre">child.mako</span></code> using a namespace:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp">## parent.mako</span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"base.mako"</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">namespace</span> <span class="na">name=</span><span class="s">"child"</span> <span class="na">file=</span><span class="s">"child.mako"</span><span class="cp">></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">block</span> <span class="na">name=</span><span class="s">"SectionA"</span><span class="cp">></span><span class="x"></span>
<span class="x"> </span><span class="cp">${</span><span class="n">child</span><span class="o">.</span><span class="n">SectionA</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="cp"></%</span><span class="nb">block</span><span class="cp">></span><span class="x"></span></pre></div>
</div>
</div>
<div class="section" id="inheritable-attributes">
<span id="inheritance-attr"></span><h2>Inheritable Attributes<a class="headerlink" href="#inheritable-attributes" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="namespaces.html#mako.runtime.Namespace.attr" title="mako.runtime.Namespace.attr"><code class="xref py py-attr docutils literal notranslate"><span class="pre">attr</span></code></a> accessor of the <a class="reference internal" href="namespaces.html#mako.runtime.Namespace" title="mako.runtime.Namespace"><code class="xref py py-class docutils literal notranslate"><span class="pre">Namespace</span></code></a> object
allows access to module level variables declared in a template. By accessing
<code class="docutils literal notranslate"><span class="pre">self.attr</span></code>, you can access regular attributes from the
inheritance chain as declared in <code class="docutils literal notranslate"><span class="pre"><%!</span> <span class="pre">%></span></code> sections. Such as:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%!</span>
<span class="n">class_</span> <span class="o">=</span> <span class="s2">"grey"</span>
<span class="cp">%></span><span class="x"></span>
<span class="x"><div class="</span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">attr</span><span class="o">.</span><span class="n">class_</span><span class="cp">}</span><span class="x">"></span>
<span class="x"> </span><span class="cp">${</span><span class="bp">self</span><span class="o">.</span><span class="n">body</span><span class="p">()</span><span class="cp">}</span><span class="x"></span>
<span class="x"></div></span></pre></div>
</div>
<p>If an inheriting template overrides <code class="docutils literal notranslate"><span class="pre">class_</span></code> to be
<code class="docutils literal notranslate"><span class="pre">"white"</span></code>, as in:</p>
<div class="highlight-mako notranslate"><div class="highlight"><pre><span></span><span class="cp"><%!</span>
<span class="n">class_</span> <span class="o">=</span> <span class="s2">"white"</span>
<span class="cp">%></span><span class="x"></span>
<span class="cp"><%</span><span class="nb">inherit</span> <span class="na">file=</span><span class="s">"parent.html"</span><span class="cp">/></span><span class="x"></span>
<span class="x">This is the body</span></pre></div>
</div>
<p>you’ll get output like:</p>
<div class="highlight-html notranslate"><div class="highlight"><pre><span></span><span class="p"><</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"white"</span><span class="p">></span>
This is the body
<span class="p"></</span><span class="nt">div</span><span class="p">></span></pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><a class="reference internal" href="namespaces.html#namespace-attr-for-includes"><span class="std std-ref">Version One - Use Namespace.attr</span></a> - a more sophisticated example using
<a class="reference internal" href="namespaces.html#mako.runtime.Namespace.attr" title="mako.runtime.Namespace.attr"><code class="xref py py-attr docutils literal notranslate"><span class="pre">Namespace.attr</span></code></a>.</p>
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