==================================================

The Django template language: For template authors

==================================================

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.

.. _Smarty: http://smarty.php.net/

.. _CheetahTemplate: http://www.cheetahtemplate.org/

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 always are in double quotes.

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 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 %} #}

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.

    * 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.

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

----------------------

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

~~~~~

Cycle among the given strings each time this tag is encountered.

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

    {% for o in some_list %}

        <tr class="{% cycle row1,row2 %}">

            ...

        </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,row3 as rowcolors %}">...</tr>

        <tr class="{% cycle rowcolors %}">...</tr>

        <tr class="{% cycle rowcolors %}">...</tr>

You can use any number of values, separated by commas. Make sure not to put

spaces between the values -- only commas.

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 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 %}

for

~~~

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

given ``athlete_list``::

    <ul>

    {% for athlete in athlete_list %}

        <li>{{ athlete.name }}</li>

    {% endfor %}

    </ul>

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

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 %}