Ticket #5340: templates.txt

==================================================
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 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.

    * 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
~~~~~

**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 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
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 822 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``, ``23``
                      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::

    {% ssi /home/html/ljworld.com/includes/right_generic.html %}

If the optional "parsed" parameter is given, the contents of the included
file are evaluated as template code, within the current context::

    {% ssi /home/html/ljworld.com/includes/right_generic.html parsed %}

Note that if you use ``{% ssi %}``, you'll need to define
`ALLOWED_INCLUDE_ROOTS`_ in your Django settings, as a security measure.

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

.. _ALLOWED_INCLUDE_ROOTS: ../settings/#allowed-include-roots

templatetag
~~~~~~~~~~~

Output one of the syntax characters used to compose template tags.

Since the template system has no concept of "escaping", to display one of the
bits used in template tags, you must use the ``{% templatetag %}`` tag.

The argument tells which template bit to output:

    ==================  =======
    Argument            Outputs
    ==================  =======
    ``openblock``       ``{%``
    ``closeblock``      ``%}``
    ``openvariable``    ``{{``
    ``closevariable``   ``}}``
    ``openbrace``       ``{``
    ``closebrace``      ``}``
    ``opencomment``     ``{#``
    ``closecomment``    ``#}``
    ==================  =======

url
~~~

**Note that the syntax for this tag may change in the future, as we make it more robust.**

Returns an absolute URL (i.e., a URL without the domain name) matching a given
view function and optional parameters. This is a way to output links without
violating the DRY principle by having to hard-code URLs in your templates::

    {% url path.to.some_view arg1,arg2,name1=value1 %}

The first argument is a path to a view function in the format
``package.package.module.function``. Additional arguments are optional and
should be comma-separated values that will be used as positional and keyword
arguments in the URL. All arguments required by the URLconf should be present.

For example, suppose you have a view, ``app_views.client``, whose URLconf
takes a client ID (here, ``client()`` is a method inside the views file
``app_views.py``). The URLconf line might look like this::

    ('^client/(\d+)/$', 'app_views.client')

If this app's URLconf is included into the project's URLconf under a path
such as this::

    ('^clients/', include('project_name.app_name.urls'))

...then, in a template, you can create a link to this view like this::

    {% url app_views.client client.id %}

The template tag will output the string ``/clients/client/123/``.

**New in development version:** If you're using `named URL patterns`_,
you can refer to the name of the pattern in the ``url`` tag instead of
using the path to the view.

.. _named URL patterns: ../url_dispatch/#naming-url-patterns

widthratio
~~~~~~~~~~

For creating bar charts and such, this tag calculates the ratio of a given value
to a maximum value, and then applies that ratio to a constant.

For example::

    <img src="bar.gif" height="10" width="{% widthratio this_value max_value 100 %}" />

Above, if ``this_value`` is 175 and ``max_value`` is 200, the the image in the
above example will be 88 pixels wide (because 175/200 = .875; .875 * 100 = 87.5
which is rounded up to 88).

with
~~~~

**New in Django development version**

Caches a complex variable under a simpler name. This is useful when accessing
an "expensive" method (e.g., one that hits the database) multiple times.

For example::

    {% with business.employees.count as total %}
        {{ total }} employee{{ total|pluralize }}
    {% endwith %}

The populated variable (in the example above, ``total``) is only available
between the ``{% with %}`` and ``{% endwith %}`` tags.

Built-in filter reference
-------------------------

add
~~~

Adds the arg to the value.

addslashes
~~~~~~~~~~

Adds slashes. Useful for passing strings to JavaScript, for example.


capfirst
~~~~~~~~

Capitalizes the first character of the value.

center
~~~~~~

Centers the value in a field of a given width.

cut
~~~

Removes all values of arg from the given string.

date
~~~~

Formats a date according to the given format (same as the `now`_ tag).

default
~~~~~~~

If value is unavailable, use given default.

default_if_none
~~~~~~~~~~~~~~~

If value is ``None``, use given default.

dictsort
~~~~~~~~

Takes a list of dictionaries, returns that list sorted by the key given in
the argument.

dictsortreversed
~~~~~~~~~~~~~~~~

Takes a list of dictionaries, returns that list sorted in reverse order by the
key given in the argument.

divisibleby
~~~~~~~~~~~

Returns true if the value is divisible by the argument.

escape
~~~~~~

Escapes a string's HTML. Specifically, it makes these replacements:

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

filesizeformat
~~~~~~~~~~~~~~

Format the value like a 'human-readable' file size (i.e. ``'13 KB'``,
``'4.1 MB'``, ``'102 bytes'``, etc).

first
~~~~~

Returns the first item in a list.

fix_ampersands
~~~~~~~~~~~~~~

Replaces ampersands with ``&amp;`` entities.

floatformat
~~~~~~~~~~~

When used without an argument, rounds a floating-point number to one decimal
place -- but only if there's a decimal part to be displayed. For example:

    * ``36.123`` gets converted to ``36.1``
    * ``36.15`` gets converted to ``36.2``
    * ``36`` gets converted to ``36``

If used with a numeric integer argument, ``floatformat`` rounds a number to that
many decimal places.  For example:

    * ``36.1234`` with floatformat:3 gets converted to ``36.123``
    * ``36`` with floatformat:4 gets converted to ``36.0000``

If the argument passed to ``floatformat`` is negative, it will round a number to
that many decimal places -- but only if there's a decimal part to be displayed.
For example:

    * ``36.1234`` with floatformat:-3 gets converted to ``36.123``
    * ``36`` with floatformat:-4 gets converted to ``36``

Using ``floatformat`` with no argument is equivalent to using ``floatformat`` with
an argument of ``-1``.

get_digit
~~~~~~~~~

Given a whole number, returns the requested digit of it, where 1 is the
right-most digit, 2 is the second-right-most digit, etc. Returns the original
value for invalid input (if input or argument is not an integer, or if argument
is less than 1). Otherwise, output is always an integer.

iriencode
~~~~~~~~~

Converts an IRI (Internationalized Resource Identifier) to a string that is
suitable for including in a URL. This is necessary if you're trying to use
strings containing non-ASCII characters in a URL.

It's safe to use this filter on a string that has already gone through the
``urlencode`` filter.

join
~~~~

Joins a list with a string, like Python's ``str.join(list)``.

length
~~~~~~

Returns the length of the value. Useful for lists.

length_is
~~~~~~~~~

Returns a boolean of whether the value's length is the argument.

linebreaks
~~~~~~~~~~

Converts newlines into ``<p>`` and ``<br />`` tags.

linebreaksbr
~~~~~~~~~~~~

Converts newlines into ``<br />`` tags.

linenumbers
~~~~~~~~~~~

Displays text with line numbers.

ljust
~~~~~

Left-aligns the value in a field of a given width.

**Argument:** field size

lower
~~~~~

Converts a string into all lowercase.

make_list
~~~~~~~~~

Returns the value turned into a list. For an integer, it's a list of
digits. For a string, it's a list of characters.

phone2numeric
~~~~~~~~~~~~~

Converts a phone number (possibly containing letters) to its numerical
equivalent. For example, ``'800-COLLECT'`` will be converted to
``'800-2655328'``.

The input doesn't have to be a valid phone number. This will happily convert
any string.

pluralize
~~~~~~~~~

Returns a plural suffix if the value is not 1. By default, this suffix is ``'s'``.

Example::

    You have {{ num_messages }} message{{ num_messages|pluralize }}.

For words that require a suffix other than ``'s'``, you can provide an alternate
suffix as a parameter to the filter.

Example::

    You have {{ num_walruses }} walrus{{ num_walrus|pluralize:"es" }}.

For words that don't pluralize by simple suffix, you can specify both a
singular and plural suffix, separated by a comma.

Example::

    You have {{ num_cherries }} cherr{{ num_cherries|pluralize:"y,ies" }}.

pprint
~~~~~~

A wrapper around pprint.pprint -- for debugging, really.

random
~~~~~~

Returns a random item from the list.

removetags
~~~~~~~~~~

Removes a space separated list of [X]HTML tags from the output.

rjust
~~~~~

Right-aligns the value in a field of a given width.

**Argument:** field size

slice
~~~~~

Returns a slice of the list.

Uses the same syntax as Python's list slicing. See
http://diveintopython.org/native_data_types/lists.html#odbchelper.list.slice
for an introduction.

Example: ``{{ some_list|slice:":2" }}``

slugify
~~~~~~~

Converts to lowercase, removes non-word characters (alphanumerics and
underscores) and converts spaces to hyphens. Also strips leading and trailing
whitespace.

stringformat
~~~~~~~~~~~~

Formats the variable according to the argument, a string formatting specifier.
This specifier uses Python string formating syntax, with the exception that
the leading "%" is dropped.

See http://docs.python.org/lib/typesseq-strings.html for documentation of
Python string formatting

striptags
~~~~~~~~~

Strips all [X]HTML tags.

time
~~~~

Formats a time according to the given format (same as the `now`_ tag).
The time filter will only accept parameters in the format string that relate
to the time of day, not the date (for obvious reasons). If you need to
format a date, use the `date`_ filter.

timesince
~~~~~~~~~

Formats a date as the time since that date (i.e. "4 days, 6 hours").

Takes an optional argument that is a variable containing the date to use as
the comparison point (without the argument, the comparison point is *now*).
For example, if ``blog_date`` is a date instance representing midnight on 1
June 2006, and ``comment_date`` is a date instance for 08:00 on 1 June 2006,
then ``{{ comment_date|timesince:blog_date }}`` would return "8 hours".

timeuntil
~~~~~~~~~

Similar to ``timesince``, except that it measures the time from now until the
given date or datetime. For example, if today is 1 June 2006 and
``conference_date`` is a date instance holding 29 June 2006, then
``{{ conference_date|timeuntil }}`` will return "28 days".

Takes an optional argument that is a variable containing the date to use as
the comparison point (instead of *now*). If ``from_date`` contains 22 June
2006, then ``{{ conference_date|timeuntil:from_date }}`` will return "7 days".

title
~~~~~

Converts a string into titlecase.

truncatewords
~~~~~~~~~~~~~

Truncates a string after a certain number of words.

**Argument:** Number of words to truncate after

truncatewords_html
~~~~~~~~~~~~~~~~~~

Similar to ``truncatewords``, except that it is aware of HTML tags. Any tags
that are opened in the string and not closed before the truncation point, are
closed immediately after the truncation.

This is less efficient than ``truncatewords``, so should only be used when it
is being passed HTML text.

unordered_list
~~~~~~~~~~~~~~

Recursively takes a self-nested list and returns an HTML unordered list --
WITHOUT opening and closing <ul> tags.

**Changed in Django development version**

The format accepted by ``unordered_list`` has changed to an easier to
understand format.

The list is assumed to be in the proper format. For example, if ``var`` contains
``['States', ['Kansas', ['Lawrence', 'Topeka'], 'Illinois']]``, then
``{{ var|unordered_list }}`` would return::

    <li>States
    <ul>
            <li>Kansas
            <ul>
                    <li>Lawrence</li>
                    <li>Topeka</li>
            </ul>
            </li>
            <li>Illinois</li>
    </ul>
    </li>

Note: the previous more restrictive and verbose format is still supported:
``['States', [['Kansas', [['Lawrence', []], ['Topeka', []]]], ['Illinois', []]]]``,

upper
~~~~~

Converts a string into all uppercase.

urlencode
~~~~~~~~~

Escapes a value for use in a URL.

urlize
~~~~~~

Converts URLs in plain text into clickable links.

Note that if ``urlize`` is applied to text that already contains HTML markup,
things won't work as expected. Apply this filter only to *plain* text.

urlizetrunc
~~~~~~~~~~~

Converts URLs into clickable links, truncating URLs longer than the given
character limit.

As with urlize_, this filter should only be applied to *plain* text.

**Argument:** Length to truncate URLs to

wordcount
~~~~~~~~~

Returns the number of words.

wordwrap
~~~~~~~~

Wraps words at specified line length.

**Argument:** number of characters at which to wrap the text

yesno
~~~~~

Given a string mapping values for true, false and (optionally) None,
returns one of those strings according to the value:

==========  ======================  ==================================
Value       Argument                Outputs
==========  ======================  ==================================
``True``    ``"yeah,no,maybe"``     ``yeah``
``False``   ``"yeah,no,maybe"``     ``no``
``None``    ``"yeah,no,maybe"``     ``maybe``
``None``    ``"yeah,no"``           ``"no"`` (converts None to False
                                    if no mapping for None is given)
==========  ======================  ==================================

Other tags and filter libraries
===============================

Django comes with a couple of other template-tag libraries that you have to
enable explicitly in your ``INSTALLED_APPS`` setting and enable in your
template with the ``{% load %}`` tag.

django.contrib.humanize
-----------------------

A set of Django template filters useful for adding a "human touch" to data. See
the `humanize documentation`_.

.. _humanize documentation: ../add_ons/#humanize

django.contrib.markup
---------------------

A collection of template filters that implement these common markup languages:

    * Textile
    * Markdown
    * ReST (ReStructured Text)

django.contrib.webdesign
------------------------

A collection of template tags that can be useful while designing a website,
such as a generator of Lorem Ipsum text. See the `webdesign documentation`_.

.. _webdesign documentation: ../webdesign/

Next steps
==========

Read the document `The Django template language: For Python programmers`_ if
you're interested in learning the template system from a technical
perspective -- how it works and how to extend it.

.. _The Django template language\: For Python programmers: ../templates_python/