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diff --git a/parts/django/docs/topics/templates.txt b/parts/django/docs/topics/templates.txt deleted file mode 100644 index d249bd3..0000000 --- a/parts/django/docs/topics/templates.txt +++ /dev/null @@ -1,617 +0,0 @@ -============================ -The Django template language -============================ - -.. 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 :doc:`/ref/templates/api`. - -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 :ttag:`if` tag for boolean tests, a :ttag:`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 :doc:`your own extensions - </howto/custom-template-tags>` 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/ - -Templates -========= - -.. highlightlang:: html+django - -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. - -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:", " }}``. - -Django provides about thirty built-in template filters. You can read all about -them in the :ref:`built-in filter reference <ref-templates-builtins-filters>`. -To give you a taste of what's available, here are some of the more commonly used -template filters: - - :tfilter:`default` - If a variable is false or empty, use given default. Otherwise, use the - value of the variable - - For example:: - - {{ value|default:"nothing" }} - - If ``value`` isn't provided or is empty, the above will display - "``nothing``". - - :tfilter:`length` - Returns the length of the value. This works for both strings and lists; - for example:: - - {{ value|length }} - - If ``value`` is ``['a', 'b', 'c', 'd']``, the output will be ``4``. - - :tfilter:`striptags` - Strips all [X]HTML tags. For example:: - - {{ value|striptags }} - - If ``value`` is ``"<b>Joel</b> <button>is</button> a - <span>slug</span>"``, the output will be ``"Joel is a slug"``. - -Again, these are just a few examples; see the :ref:`built-in filter reference -<ref-templates-builtins-filters>` for the complete list. - -You can also create your own custom template filters; see -:doc:`/howto/custom-template-tags`. - -.. seealso:: - - Django's admin interface can include a complete reference of all template - tags and filters available for a given site. See - :doc:`/ref/contrib/admin/admindocs`. - -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 %}``). - -Django ships with about two dozen built-in template tags. You can read all about -them in the :ref:`built-in tag reference <ref-templates-builtins-tags>`. To give -you a taste of what's available, here are some of the more commonly used -tags: - - :ttag:`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> - - :ttag:`if` and ``else`` - Evaluates a variable, and if that variable is "true" the contents of the - block are displayed:: - - {% 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. - - You can also use filters and various operators in the ``if`` tag:: - - {% if athlete_list|length > 1 %} - Team: {% for athlete in athlete_list %} ... {% endfor %} - {% else %} - Athlete: {{ athlete_list.0.name }} - {% endif %} - - :ttag:`block` and :ttag:`extends` - Set up `template inheritance`_ (see below), a powerful way - of cutting down on "boilerplate" in templates. - -Again, the above is only a selection of the whole list; see the :ref:`built-in -tag reference <ref-templates-builtins-tags>` for the complete list. - -You can also create your own custom template tags; see -:doc:`/howto/custom-template-tags`. - -.. seealso:: - - Django's admin interface can include a complete reference of all template - tags and filters available for a given site. See - :doc:`/ref/contrib/admin/admindocs`. - -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 :ttag:`comment` tag. - -.. _template-inheritance: - -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: - -Automatic HTML escaping -======================= - -.. versionadded:: 1.0 - -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 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 Django, every template automatically escapes the output -of every variable tag. Specifically, these five characters are -escaped: - - * ``<`` is converted to ``<`` - * ``>`` is converted to ``>`` - * ``'`` (single quote) is converted to ``'`` - * ``"`` (double quote) is converted to ``"`` - * ``&`` is converted to ``&`` - -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: <b> - 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 < 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. - -.. _loading-custom-template-libraries: - -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 %} - -See :doc:`/howto/custom-template-tags` for information on writing your own custom -template libraries. - -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. |