root/django/trunk/docs/templates.txt

==================================================
The Django template language: For template authors
==================================================

.. admonition:: About this document

    This document explains the language syntax of the Django template system. If
    you're looking for a more technical perspective on how it works and how to
    extend it, see `The Django template language: For Python programmers`_.

Django's template language is designed to strike a balance between power and
ease. It's designed to feel comfortable to those used to working with HTML. If
you have any exposure to other text-based template languages, such as Smarty_
or CheetahTemplate_, you should feel right at home with Django's templates.

.. admonition:: Philosophy

    If you have a background in programming, or if you're used to languages
    like PHP which mix programming code directly into HTML, you'll want to
    bear in mind that the Django template system is not simply Python embedded
    into HTML. This is by design: the template system is meant to express
    presentation, not program logic.

    The Django template system provides tags which function similarly to some
    programming constructs -- an ``{% if %}`` tag for boolean tests, a ``{%
    for %}`` tag for looping, etc. -- but these are not simply executed as the
    corresponding Python code, and the template system will not execute
    arbitrary Python expressions. Only the tags, filters and syntax listed
    below are supported by default (although you can add `your own
    extensions`_ to the template language as needed).

.. _`The Django template language: For Python programmers`: ../templates_python/
.. _Smarty: http://smarty.php.net/
.. _CheetahTemplate: http://www.cheetahtemplate.org/
.. _your own extensions: ../templates_python/#extending-the-template-system

Templates
=========

A template is simply a text file. It can generate any text-based format (HTML,
XML, CSV, etc.).

A template contains **variables**, which get replaced with values when the
template is evaluated, and **tags**, which control the logic of the template.

Below is a minimal template that illustrates a few basics. Each element will be
explained later in this document.::

    {% extends "base_generic.html" %}

    {% block title %}{{ section.title }}{% endblock %}

    {% block content %}
    <h1>{{ section.title }}</h1>

    {% for story in story_list %}
    <h2>
      <a href="{{ story.get_absolute_url }}">
        {{ story.headline|upper }}
      </a>
    </h2>
    <p>{{ story.tease|truncatewords:"100" }}</p>
    {% endfor %}
    {% endblock %}

.. admonition:: Philosophy

    Why use a text-based template instead of an XML-based one (like Zope's
    TAL)? We wanted Django's template language to be usable for more than
    just XML/HTML templates. At World Online, we use it for e-mails,
    JavaScript and CSV. You can use the template language for any text-based
    format.

    Oh, and one more thing: Making humans edit XML is sadistic!

Variables
=========

Variables look like this: ``{{ variable }}``. When the template engine
encounters a variable, it evaluates that variable and replaces it with the
result.

Use a dot (``.``) to access attributes of a variable.

.. admonition:: Behind the scenes

    Technically, when the template system encounters a dot, it tries the
    following lookups, in this order:

        * Dictionary lookup
        * Attribute lookup
        * Method call
        * List-index lookup

In the above example, ``{{ section.title }}`` will be replaced with the
``title`` attribute of the ``section`` object.

If you use a variable that doesn't exist, the template system will insert
the value of the ``TEMPLATE_STRING_IF_INVALID`` setting, which is set to ``''``
(the empty string) by default.

See `Using the built-in reference`_, below, for help on finding what variables
are available in a given template.

Filters
=======

You can modify variables for display by using **filters**.

Filters look like this: ``{{ name|lower }}``. This displays the value of the
``{{ name }}`` variable after being filtered through the ``lower`` filter,
which converts text to lowercase. Use a pipe (``|``) to apply a filter.

Filters can be "chained." The output of one filter is applied to the next.
``{{ text|escape|linebreaks }}`` is a common idiom for escaping text contents,
then converting line breaks to ``<p>`` tags.

Some filters take arguments. A filter argument looks like this: ``{{
bio|truncatewords:30 }}``. This will display the first 30 words of the ``bio``
variable.

Filter arguments that contain spaces must be quoted; for example, to join a list
with commas and spaced you'd use ``{{ list|join:", " }}``.

The `Built-in filter reference`_ below describes all the built-in filters.

Tags
====

Tags look like this: ``{% tag %}``. Tags are more complex than variables: Some
create text in the output, some control flow by performing loops or logic, and
some load external information into the template to be used by later variables.

Some tags require beginning and ending tags (i.e.
``{% tag %} ... tag contents ... {% endtag %}``). The `Built-in tag reference`_
below describes all the built-in tags. You can create your own tags, if you
know how to write Python code.

Comments
========

To comment-out part of a line in a template, use the comment syntax: ``{# #}``.

For example, this template would render as ``'hello'``::

    {# greeting #}hello

A comment can contain any template code, invalid or not. For example::

    {# {% if foo %}bar{% else %} #}

This syntax can only be used for single-line comments (no newlines are
permitted between the ``{#`` and ``#}`` delimiters). If you need to comment
out a multiline portion of the template, see the ``comment`` tag, below__.

__ comment_

Template inheritance
====================

The most powerful -- and thus the most complex -- part of Django's template
engine is template inheritance. Template inheritance allows you to build a base
"skeleton" template that contains all the common elements of your site and
defines **blocks** that child templates can override.

It's easiest to understand template inheritance by starting with an example::

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
    <head>
        <link rel="stylesheet" href="style.css" />
        <title>{% block title %}My amazing site{% endblock %}</title>
    </head>

    <body>
        <div id="sidebar">
            {% block sidebar %}
            <ul>
                <li><a href="/">Home</a></li>
                <li><a href="/blog/">Blog</a></li>
            </ul>
            {% endblock %}
        </div>

        <div id="content">
            {% block content %}{% endblock %}
        </div>
    </body>
    </html>

This template, which we'll call ``base.html``, defines a simple HTML skeleton
document that you might use for a simple two-column page. It's the job of
"child" templates to fill the empty blocks with content.

In this example, the ``{% block %}`` tag defines three blocks that child
templates can fill in. All the ``block`` tag does is to tell the template
engine that a child template may override those portions of the template.

A child template might look like this::

    {% extends "base.html" %}

    {% block title %}My amazing blog{% endblock %}

    {% block content %}
    {% for entry in blog_entries %}
        <h2>{{ entry.title }}</h2>
        <p>{{ entry.body }}</p>
    {% endfor %}
    {% endblock %}

The ``{% extends %}`` tag is the key here. It tells the template engine that
this template "extends" another template. When the template system evaluates
this template, first it locates the parent -- in this case, "base.html".

At that point, the template engine will notice the three ``{% block %}`` tags
in ``base.html`` and replace those blocks with the contents of the child
template. Depending on the value of ``blog_entries``, the output might look
like::

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
    <head>
        <link rel="stylesheet" href="style.css" />
        <title>My amazing blog</title>
    </head>

    <body>
        <div id="sidebar">
            <ul>
                <li><a href="/">Home</a></li>
                <li><a href="/blog/">Blog</a></li>
            </ul>
        </div>

        <div id="content">
            <h2>Entry one</h2>
            <p>This is my first entry.</p>

            <h2>Entry two</h2>
            <p>This is my second entry.</p>
        </div>
    </body>
    </html>

Note that since the child template didn't define the ``sidebar`` block, the
value from the parent template is used instead. Content within a ``{% block %}``
tag in a parent template is always used as a fallback.

You can use as many levels of inheritance as needed. One common way of using
inheritance is the following three-level approach:

    * Create a ``base.html`` template that holds the main look-and-feel of your
      site.
    * Create a ``base_SECTIONNAME.html`` template for each "section" of your
      site. For example, ``base_news.html``, ``base_sports.html``. These
      templates all extend ``base.html`` and include section-specific
      styles/design.
    * Create individual templates for each type of page, such as a news
      article or blog entry. These templates extend the appropriate section
      template.

This approach maximizes code reuse and makes it easy to add items to shared
content areas, such as section-wide navigation.

Here are some tips for working with inheritance:

    * If you use ``{% extends %}`` in a template, it must be the first template
      tag in that template. Template inheritance won't work, otherwise.

    * More ``{% block %}`` tags in your base templates are better. Remember,
      child templates don't have to define all parent blocks, so you can fill
      in reasonable defaults in a number of blocks, then only define the ones
      you need later. It's better to have more hooks than fewer hooks.

    * If you find yourself duplicating content in a number of templates, it
      probably means you should move that content to a ``{% block %}`` in a
      parent template.

    * If you need to get the content of the block from the parent template,
      the ``{{ block.super }}`` variable will do the trick. This is useful
      if you want to add to the contents of a parent block instead of
      completely overriding it. Data inserted using ``{{ block.super }}`` will
      not be automatically escaped (see the `next section`_), since it was
      already escaped, if necessary, in the parent template.

    * For extra readability, you can optionally give a *name* to your
      ``{% endblock %}`` tag. For example::

          {% block content %}
          ...
          {% endblock content %}

      In larger templates, this technique helps you see which ``{% block %}``
      tags are being closed.

Finally, note that you can't define multiple ``{% block %}`` tags with the same
name in the same template. This limitation exists because a block tag works in
"both" directions. That is, a block tag doesn't just provide a hole to fill --
it also defines the content that fills the hole in the *parent*. If there were
two similarly-named ``{% block %}`` tags in a template, that template's parent
wouldn't know which one of the blocks' content to use.

.. _next section: #automatic-html-escaping

Automatic HTML escaping
=======================

**New in Django development version**

When generating HTML from templates, there's always a risk that a variable will
include characters that affect the resulting HTML. For example, consider this
template fragment::

    Hello, {{ name }}.

At first, this seems like a harmless way to display a user's name, but consider
what would happen if the user entered his name as this::

    <script>alert('hello')</script>

With this name value, the template would be rendered as::

    Hello, <script>alert('hello')</script>

...which means the browser would pop-up a JavaScript alert box!

Similarly, what if the name contained a ``'<'`` symbol, like this?

    <b>username

That would result in a rendered template like this::

    Hello, <b>username

...which, in turn, would result in the remainder of the Web page being bolded!

Clearly, user-submitted data shouldn't be trusted blindly and inserted directly
into your Web pages, because a malicious user could use this kind of hole to
do potentially bad things. This type of security exploit is called a
`Cross Site Scripting`_ (XSS) attack.

To avoid this problem, you have two options:

    * One, you can make sure to run each untrusted variable through the
      ``escape`` filter (documented below), which converts potentially harmful
      HTML characters to unharmful ones. This was default the default solution
      in Django for its first few years, but the problem is that it puts the
      onus on *you*, the developer / template author, to ensure you're escaping
      everything. It's easy to forget to escape data.

    * Two, you can take advantage of Django's automatic HTML escaping. The
      remainder of this section describes how auto-escaping works.

By default in the Django development version, every template automatically
escapes the output of every variable tag. Specifically, these five characters
are escaped:

    * ``<`` is converted to ``&lt;``
    * ``>`` is converted to ``&gt;``
    * ``'`` (single quote) is converted to ``&#39;``
    * ``"`` (double quote) is converted to ``&quot;``
    * ``&`` is converted to ``&amp;``

Again, we stress that this behavior is on by default. If you're using Django's
template system, you're protected.

.. _Cross Site Scripting: http://en.wikipedia.org/wiki/Cross-site_scripting

How to turn it off
------------------

If you don't want data to be auto-escaped, on a per-site, per-template level or
per-variable level, you can turn it off in several ways.

Why would you want to turn it off? Because sometimes, template variables
contain data that you *intend* to be rendered as raw HTML, in which case you
don't want their contents to be escaped. For example, you might store a blob of
HTML in your database and want to embed that directly into your template. Or,
you might be using Django's template system to produce text that is *not* HTML
-- like an e-mail message, for instance.

For individual variables
~~~~~~~~~~~~~~~~~~~~~~~~

To disable auto-escaping for an individual variable, use the ``safe`` filter::

    This will be escaped: {{ data }}
    This will not be escaped: {{ data|safe }}

Think of *safe* as shorthand for *safe from further escaping* or *can be
safely interpreted as HTML*. In this example, if ``data`` contains ``'<b>'``,
the output will be::

    This will be escaped: &lt;b&gt;
    This will not be escaped: <b>

For template blocks
~~~~~~~~~~~~~~~~~~~

To control auto-escaping for a template, wrap the template (or just a
particular section of the template) in the ``autoescape`` tag, like so::

    {% autoescape off %}
        Hello {{ name }}
    {% endautoescape %}

The ``autoescape`` tag takes either ``on`` or ``off`` as its argument. At
times, you might want to force auto-escaping when it would otherwise be
disabled. Here is an example template::

    Auto-escaping is on by default. Hello {{ name }}

    {% autoescape off %}
        This will not be auto-escaped: {{ data }}.

        Nor this: {{ other_data }}
        {% autoescape on %}
            Auto-escaping applies again: {{ name }}
        {% endautoescape %}
    {% endautoescape %}

The auto-escaping tag passes its effect onto templates that extend the
current one as well as templates included via the ``include`` tag, just like
all block tags. For example::

    # base.html

    {% autoescape off %}
    <h1>{% block title %}{% endblock %}</h1>
    {% block content %}
    {% endblock %}
    {% endautoescape %}


    # child.html

    {% extends "base.html" %}
    {% block title %}This & that{% endblock %}
    {% block content %}{{ greeting }}{% endblock %}

Because auto-escaping is turned off in the base template, it will also be
turned off in the child template, resulting in the following rendered
HTML when the ``greeting`` variable contains the string ``<b>Hello!</b>``::

    <h1>This & that</h1>
    <b>Hello!</b>

Notes
-----

Generally, template authors don't need to worry about auto-escaping very much.
Developers on the Python side (people writing views and custom filters) need to
think about the cases in which data shouldn't be escaped, and mark data
appropriately, so things Just Work in the template.

If you're creating a template that might be used in situations where you're
not sure whether auto-escaping is enabled, then add an ``escape`` filter to any
variable that needs escaping. When auto-escaping is on, there's no danger of
the ``escape`` filter *double-escaping* data -- the ``escape`` filter does not
affect auto-escaped variables.

String literals and automatic escaping
--------------------------------------

As we mentioned earlier, filter arguments can be strings::

    {{ data|default:"This is a string literal." }}

All string literals are inserted **without** any automatic escaping into the
template -- they act as if they were all passed through the ``safe`` filter.
The reasoning behind this is that the template author is in control of what
goes into the string literal, so they can make sure the text is correctly
escaped when the template is written.

This means you would write ::

    {{ data|default:"3 &gt; 2" }}

...rather than ::

    {{ data|default:"3 > 2" }}  <-- Bad! Don't do this.

This doesn't affect what happens to data coming from the variable itself.
The variable's contents are still automatically escaped, if necessary, because
they're beyond the control of the template author.

Using the built-in reference
============================

Django's admin interface includes a complete reference of all template tags and
filters available for a given site. To see it, go to your admin interface and
click the "Documentation" link in the upper right of the page.

The reference is divided into 4 sections: tags, filters, models, and views.

The **tags** and **filters** sections describe all the built-in tags (in fact,
the tag and filter references below come directly from those pages) as well as
any custom tag or filter libraries available.

The **views** page is the most valuable. Each URL in your site has a separate
entry here, and clicking on a URL will show you:

    * The name of the view function that generates that view.
    * A short description of what the view does.
    * The **context**, or a list of variables available in the view's template.
    * The name of the template or templates that are used for that view.

Each view documentation page also has a bookmarklet that you can use to jump
from any page to the documentation page for that view.

Because Django-powered sites usually use database objects, the **models**
section of the documentation page describes each type of object in the system
along with all the fields available on that object.

Taken together, the documentation pages should tell you every tag, filter,
variable and object available to you in a given template.

Custom tag and filter libraries
===============================

Certain applications provide custom tag and filter libraries. To access them in
a template, use the ``{% load %}`` tag::

    {% load comments %}

    {% comment_form for blogs.entries entry.id with is_public yes %}

In the above, the ``load`` tag loads the ``comments`` tag library, which then
makes the ``comment_form`` tag available for use. Consult the documentation
area in your admin to find the list of custom libraries in your installation.

The ``{% load %}`` tag can take multiple library names, separated by spaces.
Example::

    {% load comments i18n %}

Custom libraries and template inheritance
-----------------------------------------

When you load a custom tag or filter library, the tags/filters are only made
available to the current template -- not any parent or child templates along
the template-inheritance path.

For example, if a template ``foo.html`` has ``{% load comments %}``, a child
template (e.g., one that has ``{% extends "foo.html" %}``) will *not* have
access to the comments template tags and filters. The child template is
responsible for its own ``{% load comments %}``.

This is a feature for the sake of maintainability and sanity.

Built-in tag and filter reference
=================================

For those without an admin site available, reference for the stock tags and
filters follows. Because Django is highly customizable, the reference in your
admin should be considered the final word on what tags and filters are
available, and what they do.

Built-in tag reference
----------------------

autoescape
~~~~~~~~~~

**New in Django development version**

Control the current auto-escaping behavior. This tag takes either ``on`` or
``off`` as an argument and that determines whether auto-escaping is in effect
inside the block.

When auto-escaping is in effect, all variable content has HTML escaping applied
to it before placing the result into the output (but after any filters have
been applied). This is equivalent to manually applying the ``escape`` filter
to each variable.

The only exceptions are variables that are already marked as "safe" from
escaping, either by the code that populated the variable, or because it has had
the ``safe`` or ``escape`` filters applied.

block
~~~~~

Define a block that can be overridden by child templates. See
`Template inheritance`_ for more information.

comment
~~~~~~~

Ignore everything between ``{% comment %}`` and ``{% endcomment %}``

cycle
~~~~~

**Changed in Django development version**
Cycle among the given strings or variables each time this tag is encountered.

Within a loop, cycles among the given strings/variables each time through the
loop::

    {% for o in some_list %}
        <tr class="{% cycle 'row1' 'row2' rowvar %}">
            ...
        </tr>
    {% endfor %}

Outside of a loop, give the values a unique name the first time you call it,
then use that name each successive time through::

        <tr class="{% cycle 'row1' 'row2' rowvar as rowcolors %}">...</tr>
        <tr class="{% cycle rowcolors %}">...</tr>
        <tr class="{% cycle rowcolors %}">...</tr>

You can use any number of values, separated by spaces. Values enclosed in
single (') or double quotes (") are treated as string literals, while values
without quotes are assumed to refer to context variables.

You can also separate values with commas::

    {% cycle row1,row2,row3 %}

In this syntax, each value will be interpreted as literal text. The
comma-based syntax exists for backwards-compatibility, and should not be
used for new projects.

debug
~~~~~

Output a whole load of debugging information, including the current context and
imported modules.

extends
~~~~~~~

Signal that this template extends a parent template.

This tag can be used in two ways:

   * ``{% extends "base.html" %}`` (with quotes) uses the literal value
     ``"base.html"`` as the name of the parent template to extend.

   * ``{% extends variable %}`` uses the value of ``variable``. If the variable
     evaluates to a string, Django will use that string as the name of the
     parent template. If the variable evaluates to a ``Template`` object,
     Django will use that object as the parent template.

See `Template inheritance`_ for more information.

filter
~~~~~~

Filter the contents of the variable through variable filters.

Filters can also be piped through each other, and they can have arguments --
just like in variable syntax.

Sample usage::

    {% filter force_escape|lower %}
        This text will be HTML-escaped, and will appear in all lowercase.
    {% endfilter %}

firstof
~~~~~~~

Outputs the first variable passed that is not False.  Outputs nothing if all the
passed variables are False.

Sample usage::

    {% firstof var1 var2 var3 %}

This is equivalent to::

    {% if var1 %}
        {{ var1 }}
    {% else %}{% if var2 %}
        {{ var2 }}
    {% else %}{% if var3 %}
        {{ var3 }}
    {% endif %}{% endif %}{% endif %}

You can also use a literal string as a fallback value in case all
passed variables are False::

    {% firstof var1 var2 var3 "fallback value" %}

for
~~~

Loop over each item in an array.  For example, to display a list of athletes
provided in ``athlete_list``::

    <ul>
    {% for athlete in athlete_list %}
        <li>{{ athlete.name }}</li>
    {% endfor %}
    </ul>

You can loop over a list in reverse by using ``{% for obj in list reversed %}``.

**New in Django development version**
If you need to loop over a list of lists, you can unpack the values
in eachs sub-list into a set of known names. For example, if your context contains
a list of (x,y) coordinates called ``points``, you could use the following
to output the list of points::

    {% for x, y in points %}
        There is a point at {{ x }},{{ y }}
    {% endfor %}

This can also be useful if you need to access the items in a dictionary.
For example, if your context contained a dictionary ``data``, the following
would display the keys and values of the dictionary::

    {% for key, value in data.items %}
        {{ key }}: {{ value }}
    {% endfor %}

The for loop sets a number of variables available within the loop:

    ==========================  ================================================
    Variable                    Description
    ==========================  ================================================
    ``forloop.counter``         The current iteration of the loop (1-indexed)
    ``forloop.counter0``        The current iteration of the loop (0-indexed)
    ``forloop.revcounter``      The number of iterations from the end of the
                                loop (1-indexed)
    ``forloop.revcounter0``     The number of iterations from the end of the
                                loop (0-indexed)
    ``forloop.first``           True if this is the first time through the loop
    ``forloop.last``            True if this is the last time through the loop
    ``forloop.parentloop``      For nested loops, this is the loop "above" the
                                current one
    ==========================  ================================================

if
~~

The ``{% if %}`` tag evaluates a variable, and if that variable is "true" (i.e.
exists, is not empty, and is not a false boolean value) the contents of the
block are output::

    {% if athlete_list %}
        Number of athletes: {{ athlete_list|length }}
    {% else %}
        No athletes.
    {% endif %}

In the above, if ``athlete_list`` is not empty, the number of athletes will be
displayed by the ``{{ athlete_list|length }}`` variable.

As you can see, the ``if`` tag can take an optional ``{% else %}`` clause that
will be displayed if the test fails.

``if`` tags may use ``and``, ``or`` or ``not`` to test a number of variables or
to negate a given variable::

    {% if athlete_list and coach_list %}
        Both athletes and coaches are available.
    {% endif %}

    {% if not athlete_list %}
        There are no athletes.
    {% endif %}

    {% if athlete_list or coach_list %}
        There are some athletes or some coaches.
    {% endif %}

    {% if not athlete_list or coach_list %}
        There are no athletes or there are some coaches (OK, so
        writing English translations of boolean logic sounds
        stupid; it's not our fault).
    {% endif %}

    {% if athlete_list and not coach_list %}
        There are some athletes and absolutely no coaches.
    {% endif %}

``if`` tags don't allow ``and`` and ``or`` clauses within the same tag, because
the order of logic would be ambiguous. For example, this is invalid::

    {% if athlete_list and coach_list or cheerleader_list %}

If you need to combine ``and`` and ``or`` to do advanced logic, just use nested
``if`` tags. For example::

    {% if athlete_list %}
        {% if coach_list or cheerleader_list %}
            We have athletes, and either coaches or cheerleaders!
        {% endif %}
    {% endif %}

Multiple uses of the same logical operator are fine, as long as you use the
same operator. For example, this is valid::

    {% if athlete_list or coach_list or parent_list or teacher_list %}

ifchanged
~~~~~~~~~

Check if a value has changed from the last iteration of a loop.

The 'ifchanged' block tag is used within a loop. It has two possible uses.

1. Checks its own rendered contents against its previous state and only
   displays the content if it has changed. For example, this displays a list of
   days, only displaying the month if it changes::

        <h1>Archive for {{ year }}</h1>

        {% for date in days %}
            {% ifchanged %}<h3>{{ date|date:"F" }}</h3>{% endifchanged %}
            <a href="{{ date|date:"M/d"|lower }}/">{{ date|date:"j" }}</a>
        {% endfor %}

2. If given a variable, check whether that variable has changed. For
   example, the following shows the date every time it changes, but
   only shows the hour if both the hour and the date has changed::

        {% for date in days %}
            {% ifchanged date.date %} {{ date.date }} {% endifchanged %}
            {% ifchanged date.hour date.date %}
                {{ date.hour }}
            {% endifchanged %}
        {% endfor %}

ifequal
~~~~~~~

Output the contents of the block if the two arguments equal each other.

Example::

    {% ifequal user.id comment.user_id %}
        ...
    {% endifequal %}

As in the ``{% if %}`` tag, an ``{% else %}`` clause is optional.

The arguments can be hard-coded strings, so the following is valid::

    {% ifequal user.username "adrian" %}
        ...
    {% endifequal %}

It is only possible to compare an argument to template variables or strings.
You cannot check for equality with Python objects such as ``True`` or
``False``.  If you need to test if something is true or false, use the ``if``
tag instead.

ifnotequal
~~~~~~~~~~

Just like ``ifequal``, except it tests that the two arguments are not equal.

include
~~~~~~~

Loads a template and renders it with the current context. This is a way of
"including" other templates within a template.

The template name can either be a variable or a hard-coded (quoted) string,
in either single or double quotes.

This example includes the contents of the template ``"foo/bar.html"``::

    {% include "foo/bar.html" %}

This example includes the contents of the template whose name is contained in
the variable ``template_name``::

    {% include template_name %}

An included template is rendered with the context of the template that's
including it. This example produces the output ``"Hello, John"``:

    * Context: variable ``person`` is set to ``"john"``.
    * Template::

        {% include "name_snippet.html" %}

    * The ``name_snippet.html`` template::

        Hello, {{ person }}

See also: ``{% ssi %}``.

load
~~~~

Load a custom template tag set.

See `Custom tag and filter libraries`_ for more information.

now
~~~

Display the date, formatted according to the given string.

Uses the same format as PHP's ``date()`` function (http://php.net/date)
with some custom extensions.

Available format strings:

    ================  ========================================  =====================
    Format character  Description                               Example output
    ================  ========================================  =====================
    a                 ``'a.m.'`` or ``'p.m.'`` (Note that       ``'a.m.'``
                      this is slightly different than PHP's
                      output, because this includes periods
                      to match Associated Press style.)
    A                 ``'AM'`` or ``'PM'``.                     ``'AM'``
    b                 Month, textual, 3 letters, lowercase.     ``'jan'``
    B                 Not implemented.
    d                 Day of the month, 2 digits with           ``'01'`` to ``'31'``
                      leading zeros.
    D                 Day of the week, textual, 3 letters.      ``'Fri'``
    f                 Time, in 12-hour hours and minutes,       ``'1'``, ``'1:30'``
                      with minutes left off if they're zero.
                      Proprietary extension.
    F                 Month, textual, long.                     ``'January'``
    g                 Hour, 12-hour format without leading      ``'1'`` to ``'12'``
                      zeros.
    G                 Hour, 24-hour format without leading      ``'0'`` to ``'23'``
                      zeros.
    h                 Hour, 12-hour format.                     ``'01'`` to ``'12'``
    H                 Hour, 24-hour format.                     ``'00'`` to ``'23'``
    i                 Minutes.                                  ``'00'`` to ``'59'``
    I                 Not implemented.
    j                 Day of the month without leading          ``'1'`` to ``'31'``
                      zeros.
    l                 Day of the week, textual, long.           ``'Friday'``
    L                 Boolean for whether it's a leap year.     ``True`` or ``False``
    m                 Month, 2 digits with leading zeros.       ``'01'`` to ``'12'``
    M                 Month, textual, 3 letters.                ``'Jan'``
    n                 Month without leading zeros.              ``'1'`` to ``'12'``
    N                 Month abbreviation in Associated Press    ``'Jan.'``, ``'Feb.'``, ``'March'``, ``'May'``
                      style. Proprietary extension.
    O                 Difference to Greenwich time in hours.    ``'+0200'``
    P                 Time, in 12-hour hours, minutes and       ``'1 a.m.'``, ``'1:30 p.m.'``, ``'midnight'``, ``'noon'``, ``'12:30 p.m.'``
                      'a.m.'/'p.m.', with minutes left off
                      if they're zero and the special-case
                      strings 'midnight' and 'noon' if
                      appropriate. Proprietary extension.
    r                 RFC 2822 formatted date.                  ``'Thu, 21 Dec 2000 16:01:07 +0200'``
    s                 Seconds, 2 digits with leading zeros.     ``'00'`` to ``'59'``
    S                 English ordinal suffix for day of the     ``'st'``, ``'nd'``, ``'rd'`` or ``'th'``
                      month, 2 characters.
    t                 Number of days in the given month.        ``28`` to ``31``
    T                 Time zone of this machine.                ``'EST'``, ``'MDT'``
    U                 Not implemented.
    w                 Day of the week, digits without           ``'0'`` (Sunday) to ``'6'`` (Saturday)
                      leading zeros.
    W                 ISO-8601 week number of year, with        ``1``, ``53``
                      weeks starting on Monday.
    y                 Year, 2 digits.                           ``'99'``
    Y                 Year, 4 digits.                           ``'1999'``
    z                 Day of the year.                          ``0`` to ``365``
    Z                 Time zone offset in seconds. The          ``-43200`` to ``43200``
                      offset for timezones west of UTC is
                      always negative, and for those east of
                      UTC is always positive.
    ================  ========================================  =====================

Example::

    It is {% now "jS F Y H:i" %}

Note that you can backslash-escape a format string if you want to use the
"raw" value. In this example, "f" is backslash-escaped, because otherwise
"f" is a format string that displays the time. The "o" doesn't need to be
escaped, because it's not a format character::

    It is the {% now "jS o\f F" %}

This would display as "It is the 4th of September".

regroup
~~~~~~~

Regroup a list of alike objects by a common attribute.

This complex tag is best illustrated by use of an example:  say that ``people``
is a list of people represented by dictionaries with ``first_name``,
``last_name``, and ``gender`` keys::

    people = [
        {'first_name': 'George', 'last_name': 'Bush', 'gender': 'Male'},
        {'first_name': 'Bill', 'last_name': 'Clinton', 'gender': 'Male'},
        {'first_name': 'Margaret', 'last_name': 'Thatcher', 'gender': 'Female'},
        {'first_name': 'Condoleezza', 'last_name': 'Rice', 'gender': 'Female'},
        {'first_name': 'Pat', 'last_name': 'Smith', 'gender': 'Unknown'},
    ]

...and you'd like to display a hierarchical list that is ordered by gender,
like this:

    * Male:
        * George Bush
        * Bill Clinton
    * Female:
        * Margaret Thatcher
        * Condoleezza Rice
    * Unknown:
        * Pat Smith

You can use the ``{% regroup %}`` tag to group the list of people by gender.
The following snippet of template code would accomplish this::

    {% regroup people by gender as gender_list %}

    <ul>
    {% for gender in gender_list %}
        <li>{{ gender.grouper }}
        <ul>
            {% for item in gender.list %}
            <li>{{ item.first_name }} {{ item.last_name }}</li>
            {% endfor %}
        </ul>
        </li>
    {% endfor %}
    </ul>

Let's walk through this example. ``{% regroup %}`` takes three arguments: the
list you want to regroup, the attribute to group by, and the name of the
resulting list. Here, we're regrouping the ``people`` list by the ``gender``
attribute and calling the result ``gender_list``.

``{% regroup %}`` produces a list (in this case, ``gender_list``) of
**group objects**. Each group object has two attributes:

    * ``grouper`` -- the item that was grouped by (e.g., the string "Male" or
      "Female").
    * ``list`` -- a list of all items in this group (e.g., a list of all people
      with gender='Male').

Note that ``{% regroup %}`` does not order its input! Our example relies on
the fact that the ``people`` list was ordered by ``gender`` in the first place.
If the ``people`` list did *not* order its members by ``gender``, the regrouping
would naively display more than one group for a single gender. For example,
say the ``people`` list was set to this (note that the males are not grouped
together)::

    people = [
        {'first_name': 'Bill', 'last_name': 'Clinton', 'gender': 'Male'},
        {'first_name': 'Pat', 'last_name': 'Smith', 'gender': 'Unknown'},
        {'first_name': 'Margaret', 'last_name': 'Thatcher', 'gender': 'Female'},
        {'first_name': 'George', 'last_name': 'Bush', 'gender': 'Male'},
        {'first_name': 'Condoleezza', 'last_name': 'Rice', 'gender': 'Female'},
    ]

With this input for ``people``, the example ``{% regroup %}`` template code
above would result in the following output:

    * Male:
        * Bill Clinton
    * Unknown:
        * Pat Smith
    * Female:
        * Margaret Thatcher
    * Male:
        * George Bush
    * Female:
        * Condoleezza Rice

The easiest solution to this gotcha is to make sure in your view code that the
data is ordered according to how you want to display it.

Another solution is to sort the data in the template using the ``dictsort``
filter, if your data is in a list of dictionaries::

    {% regroup people|dictsort:"gender" by gender as gender_list %}

spaceless
~~~~~~~~~

Removes whitespace between HTML tags. This includes tab
characters and newlines.

Example usage::

    {% spaceless %}
        <p>
            <a href="foo/">Foo</a>
        </p>
    {% endspaceless %}

This example would return this HTML::

    <p><a href="foo/">Foo</a></p>

Only space between *tags* is removed -- not space between tags and text. In
this example, the space around ``Hello`` won't be stripped::

    {% spaceless %}
        <strong>
            Hello
        </strong>
    {% endspaceless %}

ssi
~~~

Output the contents of a given file into the page.

Like a simple "include" tag, ``{% ssi %}`` includes the contents of another
file -- which must be specified using an absolute path -- in the current
page::
</