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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
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<html>
<head>
<title>Developer Quickstart — Jinja Documentation</title>
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</style>
</head>
<body>
<div id="content">
<h1 class="heading"><span>Jinja</span></h1>
<h2 class="subheading">Developer Quickstart</h2>
<div id="toc">
<h2>Navigation</h2>
<ul>
<li><a href="index.html">back to index</a></li>
</ul>
<h2>Contents</h2>
<ul class="contents">
<li><a href="#starting-up">Starting Up</a></li>
<li><a href="#the-environment">The Environment</a></li>
<li><a href="#undefined-values">Undefined Values</a></li>
<li><a href="#automatic-escaping">Automatic Escaping</a></li>
<li><a href="#loading-templates-from-files">Loading Templates From Files</a></li>
<li><a href="#adding-filters">Adding Filters</a></li>
<li><a href="#adding-tests">Adding Tests</a></li>
</ul>
</div>
<div id="contentwrapper">
<p>This part of the documentation shows you how to embed Jinja into your
application.</p>
<div class="section">
<h2><a id="starting-up" name="starting-up">Starting Up</a></h2>
<p>Here the quickest way to create a template from a string and render it:</p>
<div class="syntax"><pre><span class="k">from</span> <span class="nn">jinja</span> <span class="k">import</span> <span class="n">Environment</span>
<span class="n">env</span> <span class="o">=</span> <span class="n">Environment</span><span class="p">()</span>
<span class="n">tmpl</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">from_string</span><span class="p">(</span><span class="s">'Hello {{ name }}!'</span><span class="p">)</span>
<span class="k">print</span> <span class="n">tmpl</span><span class="o">.</span><span class="n">render</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s">'John Doe'</span><span class="p">)</span>
</pre></div>
<p>This example should output the following string after execution:</p>
<pre class="literal-block">
Hello John Doe!
</pre>
<p>If you receive an error, check if you have a typo in your code. If not, have
a look at the <a class="reference" href="./installation.html">installation</a> page for troubleshooting.</p>
<p>Basically the important method on a template is the <cite>render</cite> method. It
takes either a dict or keyword arguments. All keyword arguments appear
in the template as variables.</p>
<p>So these two snippets do the same:</p>
<div class="syntax"><pre><span class="n">tmpl</span><span class="o">.</span><span class="n">render</span><span class="p">(</span>
<span class="n">knights</span><span class="o">=</span><span class="s">'we say nih'</span><span class="p">,</span>
<span class="n">spam</span><span class="o">=</span><span class="s">'and eggs'</span>
<span class="p">)</span>
</pre></div>
<div class="syntax"><pre><span class="n">tmpl</span><span class="o">.</span><span class="n">render</span><span class="p">({</span>
<span class="s">'knights'</span><span class="p">:</span> <span class="s">'we say nih'</span><span class="p">,</span>
<span class="s">'spam'</span><span class="p">:</span> <span class="s">'and eggs'</span>
<span class="p">})</span>
</pre></div>
</div>
<div class="section">
<h2><a id="the-environment" name="the-environment">The Environment</a></h2>
<p>The Jinja environment.</p>
<p>The core component of Jinja is the <cite>Environment</cite>. It contains
important shared variables like configuration, filters, tests,
globals and others.</p>
<p>Here the possible initialization parameters:</p>
<table border="1" class="docutils">
<colgroup>
<col width="36%" />
<col width="64%" />
</colgroup>
<tbody valign="top">
<tr><td><cite>block_start_string</cite> *</td>
<td>the string marking the begin of a block.
this defaults to <tt class="docutils literal"><span class="pre">'{%'</span></tt>.</td>
</tr>
<tr><td><cite>block_end_string</cite> *</td>
<td>the string marking the end of a block.
defaults to <tt class="docutils literal"><span class="pre">'%}'</span></tt>.</td>
</tr>
<tr><td><cite>variable_start_string</cite> *</td>
<td>the string marking the begin of a print
statement. defaults to <tt class="docutils literal"><span class="pre">'{{'</span></tt>.</td>
</tr>
<tr><td><cite>comment_start_string</cite> *</td>
<td>the string marking the begin of a
comment. defaults to <tt class="docutils literal"><span class="pre">'{#'</span></tt>.</td>
</tr>
<tr><td><cite>comment_end_string</cite> *</td>
<td>the string marking the end of a comment.
defaults to <tt class="docutils literal"><span class="pre">'#}'</span></tt>.</td>
</tr>
<tr><td><cite>trim_blocks</cite> *</td>
<td>If this is set to <tt class="docutils literal"><span class="pre">True</span></tt> the first newline
after a block is removed (block, not
variable tag!). Defaults to <tt class="docutils literal"><span class="pre">False</span></tt>.</td>
</tr>
<tr><td><cite>auto_escape</cite></td>
<td>If this is set to <tt class="docutils literal"><span class="pre">True</span></tt> Jinja will
automatically escape all variables using xml
escaping methods. If you don't want to
escape a string you have to wrap it in a
<tt class="docutils literal"><span class="pre">Markup</span></tt> object from the
<tt class="docutils literal"><span class="pre">jinja.datastructure</span></tt> module. If
<cite>auto_escape</cite> is <tt class="docutils literal"><span class="pre">True</span></tt> there will be also
a <tt class="docutils literal"><span class="pre">Markup</span></tt> object in the template
namespace to define partial html fragments.
Note that we do not recommend this feature.</td>
</tr>
<tr><td><cite>default_filters</cite></td>
<td>list of tuples in the form (<tt class="docutils literal"><span class="pre">filter_name</span></tt>,
<tt class="docutils literal"><span class="pre">arguments</span></tt>) where <tt class="docutils literal"><span class="pre">filter_name</span></tt> is the
name of a registered filter and
<tt class="docutils literal"><span class="pre">arguments</span></tt> a tuple with the filter
arguments. The filters specified here will
always be applied when printing data to the
template. <em>new in Jinja 1.1</em></td>
</tr>
<tr><td><cite>template_charset</cite></td>
<td>The charset of the templates. Defaults
to <tt class="docutils literal"><span class="pre">'utf-8'</span></tt>.</td>
</tr>
<tr><td><cite>charset</cite></td>
<td>Charset of all string input data. Defaults
to <tt class="docutils literal"><span class="pre">'utf-8'</span></tt>.</td>
</tr>
<tr><td><cite>namespace</cite></td>
<td>Global namespace for all templates.</td>
</tr>
<tr><td><cite>loader</cite></td>
<td>Specify a template loader.</td>
</tr>
<tr><td><cite>filters</cite></td>
<td>dict of filters or the default filters if
not defined.</td>
</tr>
<tr><td><cite>tests</cite></td>
<td>dict of tests of the default tests if not
defined.</td>
</tr>
<tr><td><cite>context_class</cite></td>
<td>the context class this template should use.
See the <cite>Context</cite> documentation for more
details.</td>
</tr>
<tr><td><cite>undefined_singleton</cite></td>
<td>The singleton value that is used for missing
variables. <em>new in Jinja 1.1</em></td>
</tr>
<tr><td><cite>disable_regexps</cite></td>
<td>Disable support for regular expresssions.</td>
</tr>
<tr><td><cite>friendly_traceback</cite></td>
<td>Set this to <cite>False</cite> to disable the developer
friendly traceback rewriting. Whenever an
runtime or syntax error occours jinja will
try to make a developer friendly traceback
that shows the error in the template line.
This however can be annoying when debugging
broken functions that are called from the
template. <em>new in Jinja 1.1</em></td>
</tr>
<tr><td><cite>translator_factory</cite></td>
<td>A callback function that is called with
the context as first argument to get the
translator for the current instance.
<em>new in Jinja 1.2</em></td>
</tr>
</tbody>
</table>
<p>All of these variables except those marked with a star (*) are
modifiable after environment initialization.</p>
<p>The environment provides the following useful functions and properties in
addition to the initialization values:</p>
<table border="1" class="docutils">
<colgroup>
<col width="35%" />
<col width="65%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">parse(source,</span> <span class="pre">filename)</span></tt></td>
<td>Parse the sourcecode and return the abstract
syntax tree. This tree of nodes is used by the
<a class="reference" href="./translators.html">translators</a> to convert the template into
executable source- or bytecode.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">lex(source,</span> <span class="pre">filename)</span></tt></td>
<td>Tokenize the given sourcecode and return a
generator of tuples in the form
<tt class="docutils literal"><span class="pre">(lineno,</span> <span class="pre">token,</span> <span class="pre">value)</span></tt>. The filename is just
used in the exceptions raised.
<strong>New in Jinja 1.1</strong></td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">from_string(source)</span></tt></td>
<td>Load and parse a template source and translate it
into eval-able Python code. This code is wrapped
within a <cite>Template</cite> class that allows you to
render it.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">get_template(name)</span></tt></td>
<td>Load a template from a loader. If the template
does not exist, you will get a <cite>TemplateNotFound</cite>
exception.</td>
</tr>
</tbody>
</table>
<p>There are also some internal functions on the environment used by the template
evaluation code to keep it sandboxed.</p>
</div>
<div class="section">
<h2><a id="undefined-values" name="undefined-values">Undefined Values</a></h2>
<p>If a template designer tries to access a not defined value the return value
will be the <cite>undefined_singleton</cite> specified in the environment. The default
one is the <cite>SilentUndefined</cite> which fails in no case. Additionally there is
a special undefined type called the <cite>ComplainingUndefined</cite> which is located
in the <cite>jinja.datastructure</cite> module. It will raise exceptions when compared
with other types, or when rendered.</p>
<p>Theoretically you can provide your own singleton by subclassing
<cite>AbstractUndefindedType</cite> and creating an instance of it using <cite>make_undefined</cite>
(both located in <cite>jinja.datastructure</cite>) but those two types should cover
the basic use cases. The <cite>Undefined</cite> object in that module exists for
backwards compatibility and is an alias for <cite>SilentUndefined</cite>.</p>
<p>To create your own undefined singleton do something like this:</p>
<div class="syntax"><pre><span class="x">from jinja.datastructure import AbstractUndefinedType, make_undefined</span>
<span class="x">class MyUndefinedType(AbstractUndefindedType):</span>
<span class="x"> __slots__ = ()</span>
<span class="x"> def __iter__(self):</span>
<span class="x"> return iter(int, 0)</span>
<span class="x"> def __reduce__(self):</span>
<span class="x"> return 'MyUndefined'</span>
<span class="x">MyUndefined = make_undefined(MyUndefinedType)</span>
</pre></div>
<p>The only thing you have to do is to override <cite>__reduce__</cite> so that it returns
the name of the singleton instance and create the instance using
<cite>make_undefined</cite>. Everything else is up to you. Note that currently attributes
on undefined objects are available in the Jinja layer too which however
will change in one of the next Jinja versions. So if you put a <cite>foo</cite> attribute
on your undefined singleton you will be able to do <tt class="docutils literal"><span class="pre">{{</span> <span class="pre">undefined.foo</span> <span class="pre">}}</span></tt>
by now but certainly not in the future.</p>
<p>This limitation currently exists because undefined is treated as normal object
and thus affected by normal getattr calls.</p>
</div>
<div class="section">
<h2><a id="automatic-escaping" name="automatic-escaping">Automatic Escaping</a></h2>
<p>Jinja provides a way for automatic escaping, but we do not recommend using it.
Because Jinja was designed as multi purpose template engine there are some
issues with automatic escaping. For example filters don't deal with markup
data. Also you can easily bypass the automatic escaping so it's not something
you can expect to "just work". Also there is a huge overhead when escaping
everything.</p>
<p>The best idea is to think about which data already contains html, which will
probably contain (eg: every user input, etc) etc. And live with self escaping.</p>
<p>That's usually a much better idea.</p>
</div>
<div class="section">
<h2><a id="loading-templates-from-files" name="loading-templates-from-files">Loading Templates From Files</a></h2>
<p>Loading templates from a string is always a bad idea. It doesn't allow template
inheritance and is also slow since it parses and compiles the template again
and again whereas loaders can cache the template code.</p>
<p>All you have to do is to define a loader and use the <cite>get_template</cite> function.</p>
<div class="syntax"><pre><span class="k">from</span> <span class="nn">jinja</span> <span class="k">import</span> <span class="n">Environment</span><span class="p">,</span> <span class="n">FileSystemLoader</span>
<span class="n">env</span> <span class="o">=</span> <span class="n">Environment</span><span class="p">(</span><span class="n">loader</span><span class="o">=</span><span class="n">FileSystemLoader</span><span class="p">(</span><span class="s">'templates'</span><span class="p">))</span>
<span class="n">tmpl</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">get_template</span><span class="p">(</span><span class="s">'index.html'</span><span class="p">)</span>
<span class="k">print</span> <span class="n">tmpl</span><span class="o">.</span><span class="n">render</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s">'John Doe'</span><span class="p">)</span>
</pre></div>
<p>This tells jinja to look for templates in the <tt class="docutils literal"><span class="pre">templates</span></tt> folder. It's a
better idea to use an absolute path here though. For a list of supported
loaders or how to write your own, head over to the <a class="reference" href="./loaders.html">loader</a> documentation.</p>
</div>
<div class="section">
<h2><a id="adding-filters" name="adding-filters">Adding Filters</a></h2>
<p>If you want to add additional filters to the environment, the best way is to
modify the <tt class="docutils literal"><span class="pre">filters</span></tt> attribute and not to pass a dict to the environment.
If you pass it a dict it will not include the default filters!</p>
<div class="syntax"><pre><span class="k">from</span> <span class="nn">mylib</span> <span class="k">import</span> <span class="n">my_cool_filter</span>
<span class="n">env</span><span class="o">.</span><span class="n">filters</span><span class="p">[</span><span class="s">'mycoolfilter'</span><span class="p">]</span> <span class="o">=</span> <span class="n">my_cool_filter</span>
</pre></div>
<p>Writing filter functions is explained in the <a class="reference" href="./filters.html">filter development</a> section.</p>
</div>
<div class="section">
<h2><a id="adding-tests" name="adding-tests">Adding Tests</a></h2>
<p>Adding additional tests works analogous to filters:</p>
<div class="syntax"><pre><span class="k">from</span> <span class="nn">mylib</span> <span class="k">import</span> <span class="n">my_cool_test</span>
<span class="n">env</span><span class="o">.</span><span class="n">tests</span><span class="p">[</span><span class="s">'mycooltest'</span><span class="p">]</span> <span class="o">=</span> <span class="n">my_cool_test</span>
</pre></div>
<p>Writing tests is explained in the <a class="reference" href="./tests.html">test development</a> section.</p>
</div>
</div>
</div>
</body>
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