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The Mako Runtime Environment
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The Mako Runtime Environment
<h2>
The Mako Runtime Environment
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<h3><a href="index.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">The Mako Runtime Environment</a><ul>
<li><a class="reference internal" href="#context">Context</a><ul>
<li><a class="reference internal" href="#the-buffer">The Buffer</a></li>
<li><a class="reference internal" href="#context-variables">Context Variables</a></li>
<li><a class="reference internal" href="#context-methods-and-accessors">Context Methods and Accessors</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-loop-context">The Loop Context</a><ul>
<li><a class="reference internal" href="#iterations">Iterations</a></li>
<li><a class="reference internal" href="#cycling">Cycling</a></li>
<li><a class="reference internal" href="#parent-loops">Parent Loops</a></li>
<li><a class="reference internal" href="#migrating-legacy-templates-that-use-the-word-loop">Migrating Legacy Templates that Use the Word “loop”</a></li>
</ul>
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<li><a class="reference internal" href="#all-the-built-in-names">All the Built-in Names</a><ul>
<li><a class="reference internal" href="#reserved-names">Reserved Names</a></li>
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<li><a class="reference internal" href="#api-reference">API Reference</a></li>
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<div class="section" id="the-mako-runtime-environment">
<span id="runtime-toplevel"></span><h1>The Mako Runtime Environment<a class="headerlink" href="#the-mako-runtime-environment" title="Permalink to this headline">¶</a></h1>
<p>This section describes a little bit about the objects and
built-in functions that are available in templates.</p>
<div class="section" id="context">
<span id="id1"></span><h2>Context<a class="headerlink" href="#context" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> is the central object that is created when
a template is first executed, and is responsible for handling
all communication with the outside world. Within the template
environment, it is available via the <a class="reference internal" href="#reserved-names"><em>reserved name</em></a>
<tt class="docutils literal"><span class="pre">context</span></tt>. The <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> includes two
major components, one of which is the output buffer, which is a
file-like object such as Python’s <tt class="docutils literal"><span class="pre">StringIO</span></tt> or similar, and
the other a dictionary of variables that can be freely
referenced within a template; this dictionary is a combination
of the arguments sent to the <a class="reference internal" href="usage.html#mako.template.Template.render" title="mako.template.Template.render"><tt class="xref py py-meth docutils literal"><span class="pre">render()</span></tt></a> function and
some built-in variables provided by Mako’s runtime environment.</p>
<div class="section" id="the-buffer">
<h3>The Buffer<a class="headerlink" href="#the-buffer" title="Permalink to this headline">¶</a></h3>
<p>The buffer is stored within the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>, and writing
to it is achieved by calling the <a class="reference internal" href="#mako.runtime.Context.write" title="mako.runtime.Context.write"><tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt></a> method
– in a template this looks like <tt class="docutils literal"><span class="pre">context.write('some</span> <span class="pre">string')</span></tt>.
You usually don’t need to care about this, as all text within a template, as
well as all expressions provided by <tt class="docutils literal"><span class="pre">${}</span></tt>, automatically send
everything to this method. The cases you might want to be aware
of its existence are if you are dealing with various
filtering/buffering scenarios, which are described in
<a class="reference internal" href="filtering.html"><em>Filtering and Buffering</em></a>, or if you want to programmatically
send content to the output stream, such as within a <tt class="docutils literal"><span class="pre"><%</span> <span class="pre">%></span></tt>
block.</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="cp"><%</span>
<span class="n">context</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">"some programmatic text"</span><span class="p">)</span>
<span class="cp">%></span><span class="x"></span>
</pre></div>
</div>
<p>The actual buffer may or may not be the original buffer sent to
the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> object, as various filtering/caching
scenarios may “push” a new buffer onto the context’s underlying
buffer stack. For this reason, just stick with
<tt class="docutils literal"><span class="pre">context.write()</span></tt> and content will always go to the topmost
buffer.</p>
</div>
<div class="section" id="context-variables">
<span id="context-vars"></span><h3>Context Variables<a class="headerlink" href="#context-variables" title="Permalink to this headline">¶</a></h3>
<p>When your template is compiled into a Python module, the body
content is enclosed within a Python function called
<tt class="docutils literal"><span class="pre">render_body</span></tt>. Other top-level defs defined in the template are
defined within their own function bodies which are named after
the def’s name with the prefix <tt class="docutils literal"><span class="pre">render_</span></tt> (i.e. <tt class="docutils literal"><span class="pre">render_mydef</span></tt>).
One of the first things that happens within these functions is
that all variable names that are referenced within the function
which are not defined in some other way (i.e. such as via
assignment, module level imports, etc.) are pulled from the
<a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> object’s dictionary of variables. This is how you’re
able to freely reference variable names in a template which
automatically correspond to what was passed into the current
<a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
<ul>
<li><p class="first"><strong>What happens if I reference a variable name that is not in
the current context?</strong> - The value you get back is a special
value called <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt>, or if the <tt class="docutils literal"><span class="pre">strict_undefined=True</span></tt> flag
is used a <tt class="docutils literal"><span class="pre">NameError</span></tt> is raised. <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> is just a simple global
variable with the class <a class="reference internal" href="#mako.runtime.Undefined" title="mako.runtime.Undefined"><tt class="xref py py-class docutils literal"><span class="pre">mako.runtime.Undefined</span></tt></a>. The
<tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> object throws an error when you call <tt class="docutils literal"><span class="pre">str()</span></tt> on
it, which is what happens if you try to use it in an
expression.</p>
</li>
<li><p class="first"><strong>UNDEFINED makes it hard for me to find what name is missing</strong> - An alternative
is to specify the option <tt class="docutils literal"><span class="pre">strict_undefined=True</span></tt>
to the <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><tt class="xref py py-class docutils literal"><span class="pre">Template</span></tt></a> or <a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><tt class="xref py py-class docutils literal"><span class="pre">TemplateLookup</span></tt></a>. This will cause
any non-present variables to raise an immediate <tt class="docutils literal"><span class="pre">NameError</span></tt>
which includes the name of the variable in its message
when <a class="reference internal" href="usage.html#mako.template.Template.render" title="mako.template.Template.render"><tt class="xref py py-meth docutils literal"><span class="pre">render()</span></tt></a> is called – <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> is not used.</p>
<div class="versionadded">
<p><span>New in version 0.3.6.</span></p>
</div>
</li>
<li><p class="first"><strong>Why not just return None?</strong> Using <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt>, or
raising a <tt class="docutils literal"><span class="pre">NameError</span></tt> is more
explicit and allows differentiation between a value of <tt class="docutils literal"><span class="pre">None</span></tt>
that was explicitly passed to the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> and a value that
wasn’t present at all.</p>
</li>
<li><p class="first"><strong>Why raise an exception when you call str() on it ? Why not
just return a blank string?</strong> - Mako tries to stick to the
Python philosophy of “explicit is better than implicit”. In
this case, it’s decided that the template author should be made
to specifically handle a missing value rather than
experiencing what may be a silent failure. Since <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt>
is a singleton object just like Python’s <tt class="docutils literal"><span class="pre">True</span></tt> or <tt class="docutils literal"><span class="pre">False</span></tt>,
you can use the <tt class="docutils literal"><span class="pre">is</span></tt> operator to check for it:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="cp">%</span> <span class="k">if</span> <span class="n">someval</span> <span class="ow">is</span> <span class="n">UNDEFINED</span><span class="p">:</span><span class="x"></span>
<span class="x"> someval is: no value</span>
<span class="cp">%</span> <span class="k">else</span><span class="p">:</span><span class="x"></span>
<span class="x"> someval is: </span><span class="cp">${</span><span class="n">someval</span><span class="cp">}</span>
<span class="cp">%</span><span class="k"> endif</span><span class="x"></span>
</pre></div>
</div>
</li>
</ul>
<p>Another facet of the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> is that its dictionary of
variables is <strong>immutable</strong>. Whatever is set when
<a class="reference internal" href="usage.html#mako.template.Template.render" title="mako.template.Template.render"><tt class="xref py py-meth docutils literal"><span class="pre">render()</span></tt></a> is called is what stays. Of course, since
its Python, you can hack around this and change values in the
context’s internal dictionary, but this will probably will not
work as well as you’d think. The reason for this is that Mako in
many cases creates copies of the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> object, which
get sent to various elements of the template and inheriting
templates used in an execution. So changing the value in your
local <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> will not necessarily make that value
available in other parts of the template’s execution. Examples
of where Mako creates copies of the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> include
within top-level def calls from the main body of the template
(the context is used to propagate locally assigned variables
into the scope of defs; since in the template’s body they appear
as inlined functions, Mako tries to make them act that way), and
within an inheritance chain (each template in an inheritance
chain has a different notion of <tt class="docutils literal"><span class="pre">parent</span></tt> and <tt class="docutils literal"><span class="pre">next</span></tt>, which
are all stored in unique <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> instances).</p>
<ul>
<li><p class="first"><strong>So what if I want to set values that are global to everyone
within a template request?</strong> - All you have to do is provide a
dictionary to your <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> when the template first
runs, and everyone can just get/set variables from that. Lets
say its called <tt class="docutils literal"><span class="pre">attributes</span></tt>.</p>
<p>Running the template looks like:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">output</span> <span class="o">=</span> <span class="n">template</span><span class="o">.</span><span class="n">render</span><span class="p">(</span><span class="n">attributes</span><span class="o">=</span><span class="p">{})</span>
</pre></div>
</div>
<p>Within a template, just reference the dictionary:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="cp"><%</span>
<span class="n">attributes</span><span class="p">[</span><span class="s">'foo'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'bar'</span>
<span class="cp">%></span><span class="x"></span>
<span class="x">'foo' attribute is: </span><span class="cp">${</span><span class="n">attributes</span><span class="p">[</span><span class="s">'foo'</span><span class="p">]</span><span class="cp">}</span><span class="x"></span>
</pre></div>
</div>
</li>
<li><p class="first"><strong>Why can’t “attributes” be a built-in feature of the
Context?</strong> - This is an area where Mako is trying to make as
few decisions about your application as it possibly can.
Perhaps you don’t want your templates to use this technique of
assigning and sharing data, or perhaps you have a different
notion of the names and kinds of data structures that should
be passed around. Once again Mako would rather ask the user to
be explicit.</p>
</li>
</ul>
</div>
<div class="section" id="context-methods-and-accessors">
<h3>Context Methods and Accessors<a class="headerlink" href="#context-methods-and-accessors" title="Permalink to this headline">¶</a></h3>
<p>Significant members of <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> include:</p>
<ul>
<li><p class="first"><tt class="docutils literal"><span class="pre">context[key]</span></tt> / <tt class="docutils literal"><span class="pre">context.get(key,</span> <span class="pre">default=None)</span></tt> -
dictionary-like accessors for the context. Normally, any
variable you use in your template is automatically pulled from
the context if it isn’t defined somewhere already. Use the
dictionary accessor and/or <tt class="docutils literal"><span class="pre">get</span></tt> method when you want a
variable that <em>is</em> already defined somewhere else, such as in
the local arguments sent to a <tt class="docutils literal"><span class="pre">%def</span></tt> call. If a key is not
present, like a dictionary it raises <tt class="docutils literal"><span class="pre">KeyError</span></tt>.</p>
</li>
<li><p class="first"><tt class="docutils literal"><span class="pre">keys()</span></tt> - all the names defined within this context.</p>
</li>
<li><p class="first"><tt class="docutils literal"><span class="pre">kwargs</span></tt> - this returns a <strong>copy</strong> of the context’s
dictionary of variables. This is useful when you want to
propagate the variables in the current context to a function
as keyword arguments, i.e.:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="cp">${</span><span class="nb">next</span><span class="o">.</span><span class="n">body</span><span class="p">(</span><span class="o">**</span><span class="n">context</span><span class="o">.</span><span class="n">kwargs</span><span class="p">)</span><span class="cp">}</span><span class="x"></span>
</pre></div>
</div>
</li>
<li><p class="first"><tt class="docutils literal"><span class="pre">write(text)</span></tt> - write some text to the current output
stream.</p>
</li>
<li><p class="first"><tt class="docutils literal"><span class="pre">lookup</span></tt> - returns the <a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><tt class="xref py py-class docutils literal"><span class="pre">TemplateLookup</span></tt></a> instance that is
used for all file-lookups within the current execution (even
though individual <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><tt class="xref py py-class docutils literal"><span class="pre">Template</span></tt></a> instances can conceivably have
different instances of a <a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><tt class="xref py py-class docutils literal"><span class="pre">TemplateLookup</span></tt></a>, only the
<a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><tt class="xref py py-class docutils literal"><span class="pre">TemplateLookup</span></tt></a> of the originally-called <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><tt class="xref py py-class docutils literal"><span class="pre">Template</span></tt></a> gets
used in a particular execution).</p>
</li>
</ul>
</div>
</div>
<div class="section" id="the-loop-context">
<span id="loop-context"></span><h2>The Loop Context<a class="headerlink" href="#the-loop-context" title="Permalink to this headline">¶</a></h2>
<p>Within <tt class="docutils literal"><span class="pre">%</span> <span class="pre">for</span></tt> blocks, the <a class="reference internal" href="#reserved-names"><em>reserved name</em></a> <tt class="docutils literal"><span class="pre">loop</span></tt>
is available. <tt class="docutils literal"><span class="pre">loop</span></tt> tracks the progress of
the <tt class="docutils literal"><span class="pre">for</span></tt> loop and makes it easy to use the iteration state to control
template behavior:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="x"><ul></span>
<span class="cp">%</span> <span class="k">for</span> <span class="n">a</span> <span class="ow">in</span> <span class="p">(</span><span class="s">"one"</span><span class="p">,</span> <span class="s">"two"</span><span class="p">,</span> <span class="s">"three"</span><span class="p">):</span><span class="x"></span>
<span class="x"> <li>Item </span><span class="cp">${</span><span class="n">loop</span><span class="o">.</span><span class="n">index</span><span class="cp">}</span><span class="x">: </span><span class="cp">${</span><span class="n">a</span><span class="cp">}</span><span class="x"></li></span>
<span class="cp">%</span><span class="k"> endfor</span><span class="x"></span>
<span class="x"></ul></span>
</pre></div>
</div>
<div class="versionadded">
<p><span>New in version 0.7.</span></p>
</div>
<div class="section" id="iterations">
<h3>Iterations<a class="headerlink" href="#iterations" title="Permalink to this headline">¶</a></h3>
<p>Regardless of the type of iterable you’re looping over, <tt class="docutils literal"><span class="pre">loop</span></tt> always tracks
the 0-indexed iteration count (available at <tt class="docutils literal"><span class="pre">loop.index</span></tt>), its parity
(through the <tt class="docutils literal"><span class="pre">loop.even</span></tt> and <tt class="docutils literal"><span class="pre">loop.odd</span></tt> bools), and <tt class="docutils literal"><span class="pre">loop.first</span></tt>, a bool
indicating whether the loop is on its first iteration. If your iterable
provides a <tt class="docutils literal"><span class="pre">__len__</span></tt> method, <tt class="docutils literal"><span class="pre">loop</span></tt> also provides access to
a count of iterations remaining at <tt class="docutils literal"><span class="pre">loop.reverse_index</span></tt> and <tt class="docutils literal"><span class="pre">loop.last</span></tt>,
a bool indicating whether the loop is on its last iteration; accessing these
without <tt class="docutils literal"><span class="pre">__len__</span></tt> will raise a <tt class="docutils literal"><span class="pre">TypeError</span></tt>.</p>
</div>
<div class="section" id="cycling">
<h3>Cycling<a class="headerlink" href="#cycling" title="Permalink to this headline">¶</a></h3>
<p>Cycling is available regardless of whether the iterable you’re using provides
a <tt class="docutils literal"><span class="pre">__len__</span></tt> method. Prior to Mako 0.7, you might have generated a simple
zebra striped list using <tt class="docutils literal"><span class="pre">enumerate</span></tt>:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="x"><ul></span>
<span class="cp">%</span> <span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">item</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">((</span><span class="s">'spam'</span><span class="p">,</span> <span class="s">'ham'</span><span class="p">,</span> <span class="s">'eggs'</span><span class="p">)):</span><span class="x"></span>
<span class="x"> <li class="</span><span class="cp">${</span><span class="s">'odd'</span> <span class="k">if</span> <span class="n">i</span> <span class="o">%</span> <span class="mi">2</span> <span class="k">else</span> <span class="s">'even'</span><span class="cp">}</span><span class="x">"></span><span class="cp">${</span><span class="n">item</span><span class="cp">}</span><span class="x"></li></span>
<span class="cp">%</span><span class="k"> endfor</span><span class="x"></span>
<span class="x"></ul></span>
</pre></div>
</div>
<p>With <tt class="docutils literal"><span class="pre">loop.cycle</span></tt>, you get the same results with cleaner code and less prep work:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="x"><ul></span>
<span class="cp">%</span> <span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="p">(</span><span class="s">'spam'</span><span class="p">,</span> <span class="s">'ham'</span><span class="p">,</span> <span class="s">'eggs'</span><span class="p">):</span><span class="x"></span>
<span class="x"> <li class="</span><span class="cp">${</span><span class="n">loop</span><span class="o">.</span><span class="n">cycle</span><span class="p">(</span><span class="s">'even'</span><span class="p">,</span> <span class="s">'odd'</span><span class="p">)</span><span class="cp">}</span><span class="x">"></span><span class="cp">${</span><span class="n">item</span><span class="cp">}</span><span class="x"></li></span>
<span class="cp">%</span><span class="k"> endfor</span><span class="x"></span>
<span class="x"></ul></span>
</pre></div>
</div>
<p>Both approaches produce output like the following:</p>
<div class="highlight-html"><div class="highlight"><pre><span class="nt"><ul></span>
<span class="nt"><li</span> <span class="na">class=</span><span class="s">"even"</span><span class="nt">></span>spam<span class="nt"></li></span>
<span class="nt"><li</span> <span class="na">class=</span><span class="s">"odd"</span><span class="nt">></span>ham<span class="nt"></li></span>
<span class="nt"><li</span> <span class="na">class=</span><span class="s">"even"</span><span class="nt">></span>eggs<span class="nt"></li></span>
<span class="nt"></ul></span>
</pre></div>
</div>
</div>
<div class="section" id="parent-loops">
<h3>Parent Loops<a class="headerlink" href="#parent-loops" title="Permalink to this headline">¶</a></h3>
<p>Loop contexts can also be transparently nested, and the Mako runtime will do
the right thing and manage the scope for you. You can access the parent loop
context through <tt class="docutils literal"><span class="pre">loop.parent</span></tt>.</p>
<p>This allows you to reach all the way back up through the loop stack by
chaining <tt class="docutils literal"><span class="pre">parent</span></tt> attribute accesses, i.e. <tt class="docutils literal"><span class="pre">loop.parent.parent....</span></tt> as
long as the stack depth isn’t exceeded. For example, you can use the parent
loop to make a checkered table:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="x"><table></span>
<span class="cp">%</span> <span class="k">for</span> <span class="n">consonant</span> <span class="ow">in</span> <span class="s">'pbj'</span><span class="p">:</span><span class="x"></span>
<span class="x"> <tr></span>
<span class="cp">%</span> <span class="k">for</span> <span class="n">vowel</span> <span class="ow">in</span> <span class="s">'iou'</span><span class="p">:</span><span class="x"></span>
<span class="x"> <td class="</span><span class="cp">${</span><span class="s">'black'</span> <span class="k">if</span> <span class="p">(</span><span class="n">loop</span><span class="o">.</span><span class="n">parent</span><span class="o">.</span><span class="n">even</span> <span class="o">==</span> <span class="n">loop</span><span class="o">.</span><span class="n">even</span><span class="p">)</span> <span class="k">else</span> <span class="s">'red'</span><span class="cp">}</span><span class="x">"></span>
<span class="x"> </span><span class="cp">${</span><span class="n">consonant</span> <span class="o">+</span> <span class="n">vowel</span><span class="cp">}</span><span class="x">t</span>
<span class="x"> </td></span>
<span class="cp">%</span><span class="k"> endfor</span><span class="x"></span>
<span class="x"> </tr></span>
<span class="cp">%</span><span class="k"> endfor</span><span class="x"></span>
<span class="x"></table></span>
</pre></div>
</div>
<div class="highlight-html"><div class="highlight"><pre><span class="nt"><table></span>
<span class="nt"><tr></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"black"</span><span class="nt">></span>
pit
<span class="nt"></td></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"red"</span><span class="nt">></span>
pot
<span class="nt"></td></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"black"</span><span class="nt">></span>
put
<span class="nt"></td></span>
<span class="nt"></tr></span>
<span class="nt"><tr></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"red"</span><span class="nt">></span>
bit
<span class="nt"></td></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"black"</span><span class="nt">></span>
bot
<span class="nt"></td></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"red"</span><span class="nt">></span>
but
<span class="nt"></td></span>
<span class="nt"></tr></span>
<span class="nt"><tr></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"black"</span><span class="nt">></span>
jit
<span class="nt"></td></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"red"</span><span class="nt">></span>
jot
<span class="nt"></td></span>
<span class="nt"><td</span> <span class="na">class=</span><span class="s">"black"</span><span class="nt">></span>
jut
<span class="nt"></td></span>
<span class="nt"></tr></span>
<span class="nt"></table></span>
</pre></div>
</div>
</div>
<div class="section" id="migrating-legacy-templates-that-use-the-word-loop">
<span id="migrating-loop"></span><h3>Migrating Legacy Templates that Use the Word “loop”<a class="headerlink" href="#migrating-legacy-templates-that-use-the-word-loop" title="Permalink to this headline">¶</a></h3>
<div class="versionchanged">
<p><span>Changed in version 0.7: </span>The <tt class="docutils literal"><span class="pre">loop</span></tt> name is now <a class="reference internal" href="#reserved-names"><em>reserved</em></a> in Mako,
which means a template that refers to a variable named <tt class="docutils literal"><span class="pre">loop</span></tt>
won’t function correctly when used in Mako 0.7.</p>
</div>
<p>To ease the transition for such systems, the feature can be disabled across the board for
all templates, then re-enabled on a per-template basis for those templates which wish
to make use of the new system.</p>
<p>First, the <tt class="docutils literal"><span class="pre">enable_loop=False</span></tt> flag is passed to either the <a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><tt class="xref py py-class docutils literal"><span class="pre">TemplateLookup</span></tt></a>
or <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><tt class="xref py py-class docutils literal"><span class="pre">Template</span></tt></a> object in use:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">lookup</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="s">'/docs'</span><span class="p">],</span> <span class="n">enable_loop</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span>
</pre></div>
</div>
<p>or:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">template</span> <span class="o">=</span> <span class="n">Template</span><span class="p">(</span><span class="s">"some template"</span><span class="p">,</span> <span class="n">enable_loop</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span>
</pre></div>
</div>
<p>An individual template can make usage of the feature when <tt class="docutils literal"><span class="pre">enable_loop</span></tt> is set to
<tt class="docutils literal"><span class="pre">False</span></tt> by switching it back on within the <tt class="docutils literal"><span class="pre"><%page></span></tt> tag:</p>
<div class="highlight-mako"><div class="highlight"><pre><span class="cp"><%</span><span class="nb">page</span> <span class="na">enable_loop=</span><span class="s">"True"</span><span class="cp">/></span>
<span class="cp">%</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">collection</span><span class="p">:</span><span class="x"></span>
<span class="x"> </span><span class="cp">${</span><span class="n">i</span><span class="cp">}</span><span class="x"> </span><span class="cp">${</span><span class="n">loop</span><span class="o">.</span><span class="n">index</span><span class="cp">}</span>
<span class="cp">%</span><span class="k"> endfor</span><span class="x"></span>
</pre></div>
</div>
<p>Using the above scheme, it’s safe to pass the name <tt class="docutils literal"><span class="pre">loop</span></tt> to the <a class="reference internal" href="usage.html#mako.template.Template.render" title="mako.template.Template.render"><tt class="xref py py-meth docutils literal"><span class="pre">Template.render()</span></tt></a>
method as well as to freely make usage of a variable named <tt class="docutils literal"><span class="pre">loop</span></tt> within a template, provided
the <tt class="docutils literal"><span class="pre"><%page></span></tt> tag doesn’t override it. New templates that want to use the <tt class="docutils literal"><span class="pre">loop</span></tt> context
can then set up <tt class="docutils literal"><span class="pre"><%page</span> <span class="pre">enable_loop="True"/></span></tt> to use the new feature without affecting
old templates.</p>
</div>
</div>
<div class="section" id="all-the-built-in-names">
<h2>All the Built-in Names<a class="headerlink" href="#all-the-built-in-names" title="Permalink to this headline">¶</a></h2>
<p>A one-stop shop for all the names Mako defines. Most of these
names are instances of <a class="reference internal" href="namespaces.html#mako.runtime.Namespace" title="mako.runtime.Namespace"><tt class="xref py py-class docutils literal"><span class="pre">Namespace</span></tt></a>, which are described
in the next section, <a class="reference internal" href="namespaces.html"><em>Namespaces</em></a>. Also, most of
these names other than <tt class="docutils literal"><span class="pre">context</span></tt>, <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt>, and <tt class="docutils literal"><span class="pre">loop</span></tt> are
also present <em>within</em> the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> itself. The names
<tt class="docutils literal"><span class="pre">context</span></tt>, <tt class="docutils literal"><span class="pre">loop</span></tt> and <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> themselves can’t be passed
to the context and can’t be substituted – see the section <a class="reference internal" href="#reserved-names"><em>Reserved Names</em></a>.</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">context</span></tt> - this is the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> object, introduced
at <a class="reference internal" href="#context"><em>Context</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">local</span></tt> - the namespace of the current template, described
in <a class="reference internal" href="namespaces.html#namespaces-builtin"><em>Built-in Namespaces</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">self</span></tt> - the namespace of the topmost template in an
inheritance chain (if any, otherwise the same as <tt class="docutils literal"><span class="pre">local</span></tt>),
mostly described in <a class="reference internal" href="inheritance.html"><em>Inheritance</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">parent</span></tt> - the namespace of the parent template in an
inheritance chain (otherwise undefined); see
<a class="reference internal" href="inheritance.html"><em>Inheritance</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">next</span></tt> - the namespace of the next template in an
inheritance chain (otherwise undefined); see
<a class="reference internal" href="inheritance.html"><em>Inheritance</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">caller</span></tt> - a “mini” namespace created when using the
<tt class="docutils literal"><span class="pre"><%call></span></tt> tag to define a “def call with content”; described
in <a class="reference internal" href="defs.html#defs-with-content"><em>Calling a Def with Embedded Content and/or Other Defs</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">loop</span></tt> - this provides access to <a class="reference internal" href="#mako.runtime.LoopContext" title="mako.runtime.LoopContext"><tt class="xref py py-class docutils literal"><span class="pre">LoopContext</span></tt></a> objects when
they are requested within <tt class="docutils literal"><span class="pre">%</span> <span class="pre">for</span></tt> loops, introduced at <a class="reference internal" href="#loop-context"><em>The Loop Context</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">capture</span></tt> - a function that calls a given def and captures
its resulting content into a string, which is returned. Usage
is described in <a class="reference internal" href="filtering.html"><em>Filtering and Buffering</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> - a global singleton that is applied to all
otherwise uninitialized template variables that were not
located within the <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> when rendering began,
unless the <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><tt class="xref py py-class docutils literal"><span class="pre">Template</span></tt></a> flag <tt class="docutils literal"><span class="pre">strict_undefined</span></tt>
is set to <tt class="docutils literal"><span class="pre">True</span></tt>. <tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> is
an instance of <a class="reference internal" href="#mako.runtime.Undefined" title="mako.runtime.Undefined"><tt class="xref py py-class docutils literal"><span class="pre">Undefined</span></tt></a>, and raises an
exception when its <tt class="docutils literal"><span class="pre">__str__()</span></tt> method is called.</li>
<li><tt class="docutils literal"><span class="pre">pageargs</span></tt> - this is a dictionary which is present in a
template which does not define any <tt class="docutils literal"><span class="pre">**kwargs</span></tt> section in its
<tt class="docutils literal"><span class="pre"><%page></span></tt> tag. All keyword arguments sent to the <tt class="docutils literal"><span class="pre">body()</span></tt>
function of a template (when used via namespaces) go here by
default unless otherwise defined as a page argument. If this
makes no sense, it shouldn’t; read the section
<a class="reference internal" href="namespaces.html#namespaces-body"><em>The body() Method</em></a>.</li>
</ul>
<div class="section" id="reserved-names">
<span id="id2"></span><h3>Reserved Names<a class="headerlink" href="#reserved-names" title="Permalink to this headline">¶</a></h3>
<p>Mako has a few names that are considered to be “reserved” and can’t be used
as variable names.</p>
<div class="versionchanged">
<p><span>Changed in version 0.7: </span>Mako raises an error if these words are found passed to the template
as context arguments, whereas in previous versions they’d be silently
ignored or lead to other error messages.</p>
</div>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">context</span></tt> - see <a class="reference internal" href="#context"><em>Context</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> - see <a class="reference internal" href="#context-vars"><em>Context Variables</em></a>.</li>
<li><tt class="docutils literal"><span class="pre">loop</span></tt> - see <a class="reference internal" href="#loop-context"><em>The Loop Context</em></a>. Note this can be disabled for legacy templates
via the <tt class="docutils literal"><span class="pre">enable_loop=False</span></tt> argument; see <a class="reference internal" href="#migrating-loop"><em>Migrating Legacy Templates that Use the Word “loop”</em></a>.</li>
</ul>
</div>
</div>
<div class="section" id="api-reference">
<h2>API Reference<a class="headerlink" href="#api-reference" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="mako.runtime.Context">
<em class="property">class </em><tt class="descclassname">mako.runtime.</tt><tt class="descname">Context</tt><big>(</big><em>buffer</em>, <em>**data</em><big>)</big><a class="headerlink" href="#mako.runtime.Context" title="Permalink to this definition">¶</a></dt>
<dd><p>Bases: <tt class="xref py py-class docutils literal"><span class="pre">object</span></tt></p>
<p>Provides runtime namespace, output buffer, and various
callstacks for templates.</p>
<p>See <a class="reference internal" href="#"><em>The Mako Runtime Environment</em></a> for detail on the usage of
<a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
<dl class="method">
<dt id="mako.runtime.Context.get">
<tt class="descname">get</tt><big>(</big><em>key</em>, <em>default=None</em><big>)</big><a class="headerlink" href="#mako.runtime.Context.get" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a value from this <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="mako.runtime.Context.keys">
<tt class="descname">keys</tt><big>(</big><big>)</big><a class="headerlink" href="#mako.runtime.Context.keys" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a list of all names established in this <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
</dd></dl>
<dl class="attribute">
<dt id="mako.runtime.Context.kwargs">
<tt class="descname">kwargs</tt><a class="headerlink" href="#mako.runtime.Context.kwargs" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the dictionary of top level keyword arguments associated
with this <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
<p>This dictionary only includes the top-level arguments passed to
<a class="reference internal" href="usage.html#mako.template.Template.render" title="mako.template.Template.render"><tt class="xref py py-meth docutils literal"><span class="pre">Template.render()</span></tt></a>. It does not include names produced within
the template execution such as local variable names or special names
such as <tt class="docutils literal"><span class="pre">self</span></tt>, <tt class="docutils literal"><span class="pre">next</span></tt>, etc.</p>
<p>The purpose of this dictionary is primarily for the case that
a <a class="reference internal" href="usage.html#mako.template.Template" title="mako.template.Template"><tt class="xref py py-class docutils literal"><span class="pre">Template</span></tt></a> accepts arguments via its <tt class="docutils literal"><span class="pre"><%page></span></tt> tag,
which are normally expected to be passed via <a class="reference internal" href="usage.html#mako.template.Template.render" title="mako.template.Template.render"><tt class="xref py py-meth docutils literal"><span class="pre">Template.render()</span></tt></a>,
except the template is being called in an inheritance context,
using the <tt class="docutils literal"><span class="pre">body()</span></tt> method. <a class="reference internal" href="#mako.runtime.Context.kwargs" title="mako.runtime.Context.kwargs"><tt class="xref py py-attr docutils literal"><span class="pre">Context.kwargs</span></tt></a> can then be
used to propagate these arguments to the inheriting template:</p>
<div class="highlight-python"><pre>${next.body(**context.kwargs)}</pre>
</div>
</dd></dl>
<dl class="attribute">
<dt id="mako.runtime.Context.lookup">
<tt class="descname">lookup</tt><a class="headerlink" href="#mako.runtime.Context.lookup" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the <a class="reference internal" href="usage.html#mako.lookup.TemplateLookup" title="mako.lookup.TemplateLookup"><tt class="xref py py-class docutils literal"><span class="pre">TemplateLookup</span></tt></a> associated
with this <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="mako.runtime.Context.pop_caller">
<tt class="descname">pop_caller</tt><big>(</big><big>)</big><a class="headerlink" href="#mako.runtime.Context.pop_caller" title="Permalink to this definition">¶</a></dt>
<dd><p>Pop a <tt class="docutils literal"><span class="pre">caller</span></tt> callable onto the callstack for this
<a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="mako.runtime.Context.push_caller">
<tt class="descname">push_caller</tt><big>(</big><em>caller</em><big>)</big><a class="headerlink" href="#mako.runtime.Context.push_caller" title="Permalink to this definition">¶</a></dt>
<dd><p>Push a <tt class="docutils literal"><span class="pre">caller</span></tt> callable onto the callstack for
this <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="mako.runtime.Context.write">
<tt class="descname">write</tt><big>(</big><em>string</em><big>)</big><a class="headerlink" href="#mako.runtime.Context.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write a string to this <a class="reference internal" href="#mako.runtime.Context" title="mako.runtime.Context"><tt class="xref py py-class docutils literal"><span class="pre">Context</span></tt></a> object’s
underlying output buffer.</p>
</dd></dl>
<dl class="method">
<dt id="mako.runtime.Context.writer">
<tt class="descname">writer</tt><big>(</big><big>)</big><a class="headerlink" href="#mako.runtime.Context.writer" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current writer function.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="mako.runtime.LoopContext">
<em class="property">class </em><tt class="descclassname">mako.runtime.</tt><tt class="descname">LoopContext</tt><big>(</big><em>iterable</em><big>)</big><a class="headerlink" href="#mako.runtime.LoopContext" title="Permalink to this definition">¶</a></dt>
<dd><p>Bases: <tt class="xref py py-class docutils literal"><span class="pre">object</span></tt></p>
<p>A magic loop variable.
Automatically accessible in any <tt class="docutils literal"><span class="pre">%</span> <span class="pre">for</span></tt> block.</p>
<p>See the section <a class="reference internal" href="#loop-context"><em>The Loop Context</em></a> for usage
notes.</p>
<dl class="docutils">
<dt><tt class="xref py py-attr docutils literal"><span class="pre">parent</span></tt> -> <a class="reference internal" href="#mako.runtime.LoopContext" title="mako.runtime.LoopContext"><tt class="xref py py-class docutils literal"><span class="pre">LoopContext</span></tt></a> or <tt class="docutils literal"><span class="pre">None</span></tt></dt>
<dd>The parent loop, if one exists.</dd>
<dt><tt class="xref py py-attr docutils literal"><span class="pre">index</span></tt> -> <cite>int</cite></dt>
<dd>The 0-based iteration count.</dd>
<dt><tt class="xref py py-attr docutils literal"><span class="pre">reverse_index</span></tt> -> <cite>int</cite></dt>
<dd>The number of iterations remaining.</dd>
<dt><tt class="xref py py-attr docutils literal"><span class="pre">first</span></tt> -> <cite>bool</cite></dt>
<dd><tt class="docutils literal"><span class="pre">True</span></tt> on the first iteration, <tt class="docutils literal"><span class="pre">False</span></tt> otherwise.</dd>
<dt><tt class="xref py py-attr docutils literal"><span class="pre">last</span></tt> -> <cite>bool</cite></dt>
<dd><tt class="docutils literal"><span class="pre">True</span></tt> on the last iteration, <tt class="docutils literal"><span class="pre">False</span></tt> otherwise.</dd>
<dt><tt class="xref py py-attr docutils literal"><span class="pre">even</span></tt> -> <cite>bool</cite></dt>
<dd><tt class="docutils literal"><span class="pre">True</span></tt> when <tt class="docutils literal"><span class="pre">index</span></tt> is even.</dd>
<dt><tt class="xref py py-attr docutils literal"><span class="pre">odd</span></tt> -> <cite>bool</cite></dt>
<dd><tt class="docutils literal"><span class="pre">True</span></tt> when <tt class="docutils literal"><span class="pre">index</span></tt> is odd.</dd>
</dl>
<dl class="method">
<dt id="mako.runtime.LoopContext.cycle">
<tt class="descname">cycle</tt><big>(</big><em>*values</em><big>)</big><a class="headerlink" href="#mako.runtime.LoopContext.cycle" title="Permalink to this definition">¶</a></dt>
<dd><p>Cycle through values as the loop progresses.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="mako.runtime.Undefined">
<em class="property">class </em><tt class="descclassname">mako.runtime.</tt><tt class="descname">Undefined</tt><a class="headerlink" href="#mako.runtime.Undefined" title="Permalink to this definition">¶</a></dt>
<dd><p>Bases: <tt class="xref py py-class docutils literal"><span class="pre">object</span></tt></p>
<p>Represents an undefined value in a template.</p>
<p>All template modules have a constant value
<tt class="docutils literal"><span class="pre">UNDEFINED</span></tt> present which is an instance of this
object.</p>
</dd></dl>
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