1 Template Designer Documentation
2 ===============================
4 .. highlight:: html+jinja
6 This document describes the syntax and semantics of the template engine and
7 will be most useful as reference to those creating Jinja templates. As the
8 template engine is very flexible the configuration from the application might
9 be slightly different from here in terms of delimiters and behavior of
16 A template is simply a text file. It can generate any text-based format
17 (HTML, XML, CSV, LaTeX, etc.). It doesn't have a specific extension,
18 ``.html`` or ``.xml`` are just fine.
20 A template contains **variables** or **expressions**, which get replaced with
21 values when the template is evaluated, and tags, which control the logic of
22 the template. The template syntax is heavily inspired by Django and Python.
24 Below is a minimal template that illustrates a few basics. We will cover
25 the details later in that document::
27 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
30 <title>My Webpage</title>
34 {% for item in navigation %}
35 <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
44 This covers the default settings. The application developer might have
45 changed the syntax from ``{% foo %}`` to ``<% foo %>`` or something similar.
47 There are two kinds of delimiers. ``{% ... %}`` and ``{{ ... }}``. The first
48 one is used to execute statements such as for-loops or assign values, the
49 latter prints the result of the expression to the template.
56 The application passes variables to the templates you can mess around in the
57 template. Variables may have attributes or elements on them you can access
58 too. How a variable looks like, heavily depends on the application providing
61 You can use a dot (``.``) to access attributes of a variable, alternative the
62 so-called "subscribe" syntax (``[]``) can be used. The following lines do
68 It's important to know that the curly braces are *not* part of the variable
69 but the print statement. If you access variables inside tags don't put the
72 If a variable or attribute does not exist you will get back an undefined
73 value. What you can do with that kind of value depends on the application
74 configuration, the default behavior is that it evaluates to an empty string
75 if printed and that you can iterate over it, but every other operation fails.
82 Variables can by modified by **filters**. Filters are separated from the
83 variable by a pipe symbol (``|``) and may have optional arguments in
84 parentheses. Multiple filters can be chained. The output of one filter is
87 ``{{ name|striptags|title }}`` for example will remove all HTML Tags from the
88 `name` and title-cases it. Filters that accept arguments have parentheses
89 around the arguments, like a function call. This example will join a list
90 by spaces: ``{{ list|join(', ') }}``.
92 The :ref:`builtin-filters` below describes all the builtin filters.
99 Beside filters there are also so called "tests" available. Tests can be used
100 to test a variable against a common expression. To test a variable or
101 expression you add `is` plus the name of the test after the variable. For
102 example to find out if a variable is defined you can do ``name is defined``
103 which will then return true or false depening on if `name` is defined.
105 Tests can accept arguments too. If the test only takes one argument you can
106 leave out the parentheses to group them. For example the following two
107 expressions do the same::
109 {% if loop.index is divisibleby 3 %}
110 {% if loop.index is divisibleby(3) %}
112 The :ref:`builtin-tests` below descibes all the builtin tests.
118 To comment-out part of a line in a template, use the comment syntax which is
119 by default set to ``{# ... #}``. This is useful to comment out parts of the
120 template for debugging or to add information for other template designers or
123 {# note: disabled template because we no longer user this
124 {% for user in users %}
129 .. _template-inheritance:
134 The most powerful part of Jinja is template inheritance. Template inheritance
135 allows you to build a base "skeleton" template that contains all the common
136 elements of your site and defines **blocks** that child templates can override.
138 Sounds complicated but is very basic. It's easiest to understand it by starting
145 This template, which we'll call ``base.html``, defines a simple HTML skeleton
146 document that you might use for a simple two-column page. It's the job of
147 "child" templates to fill the empty blocks with content::
149 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
151 <html xmlns="http://www.w3.org/1999/xhtml">
154 <link rel="stylesheet" href="style.css" />
155 <title>{% block title %}{% endblock %} - My Webpage</title>
159 <div id="content">{% block content %}{% endblock %}</div>
162 © Copyright 2008 by <a href="http://domain.invalid/">you</a>.
167 In this example, the ``{% block %}`` tags define four blocks that child templates
168 can fill in. All the `block` tag does is to tell the template engine that a
169 child template may override those portions of the template.
174 A child template might look like this::
176 {% extends "base.html" %}
177 {% block title %}Index{% endblock %}
180 <style type="text/css">
181 .important { color: #336699; }
186 <p class="important">
187 Welcome on my awsome homepage.
191 The ``{% extends %}`` tag is the key here. It tells the template engine that
192 this template "extends" another template. When the template system evaluates
193 this template, first it locates the parent. The extends tag should be the
194 first tag in the template. Everything before it is printed out normally and
197 The filename of the template depends on the template loader. For example the
198 :class:`FileSystemLoader` allows you to access other templates by giving the
199 filename. You can access templates in subdirectories with an slash::
201 {% extends "layout/default.html" %}
203 But this behavior can depend on the application embedding Jinja. Note that
204 since the child template doesn't define the ``footer`` block, the value from
205 the parent template is used instead.
207 You can't define multiple ``{% block %}`` tags with the same name in the
208 same template. This limitation exists because a block tag works in "both"
209 directions. That is, a block tag doesn't just provide a hole to fill - it
210 also defines the content that fills the hole in the *parent*. If there
211 were two similarly-named ``{% block %}`` tags in a template, that template's
212 parent wouldn't know which one of the blocks' content to use.
214 If you want to print a block multiple times you can however use the special
215 `self` variable and call the block with that name::
217 <title>{% block title %}{% endblock %}</title>
218 <h1>{{ self.title() }}</h1>
219 {% block body %}{% endblock %}
222 Unlike Python Jinja does not support multiple inheritance. So you can only have
223 one extends tag called per rendering.
229 It's possible to render the contents of the parent block by calling `super`.
230 This gives back the results of the parent block::
233 <h3>Table Of Contents</h3>
242 When generating HTML from templates, there's always a risk that a variable will
243 include characters that affect the resulting HTML. There are two approaches:
244 manually escaping each variable or automatically escaping everything by default.
246 Jinja supports both, but what is used depends on the application configuration.
247 The default configuaration is no automatic escaping for various reasons:
249 - escaping everything except of safe values will also mean that Jinja is
250 escaping variables known to not include HTML such as numbers which is
251 a huge performance hit.
253 - The information about the safety of a variable is very fragile. It could
254 happen that by coercing safe and unsafe values the return value is double
257 Working with Manual Escaping
258 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
260 If manual escaping is enabled it's **your** responsibility to escape
261 variables if needed. What to escape? If you have a variable that *may*
262 include any of the following chars (``>``, ``<``, ``&``, or ``"``) you
263 **have to** escape it unless the variable contains well-formed and trusted
264 HTML. Escaping works by piping the variable through the ``|e`` filter:
265 ``{{ user.username|e }}``.
267 Working with Automatic Escaping
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
270 When automatic escaping is enabled everything is escaped by default except
271 for values explicitly marked as safe. Those can either be marked by the
272 application or in the template by using the `|safe` filter. The main
273 problem with this approach is that Python itself doesn't have the concept
274 of tainted values so the information if a value is safe or unsafe can get
275 lost. If the information is lost escaping will take place which means that
276 you could end up with double escaped contents.
278 Double escaping is easy to avoid however, just relay on the tools Jinja2
279 provides and don't use builtin Python constructs such as the string modulo
282 Functions returning template data (macros, `super`, `self.BLOCKNAME`) return
285 String literals in templates with automatic escaping are considered unsafe
286 too. The reason for this is that the safe string is an extension to Python
287 and not every library will work properly with it.
290 List of Control Structures
291 --------------------------
293 A control structure refers to all those things that control the flow of a
294 program - conditionals (i.e. if/elif/else), for-loops, as well as things like
295 macros and blocks. Control structures appear inside ``{% ... %}`` blocks
296 in the default syntax.
301 Loop over each item in a sequece. For example, to display a list of users
302 provided in a variable called `users`::
306 {% for user in users %}
307 <li>{{ user.username|e }}</li>
311 Inside of a for loop block you can access some special variables:
313 +-----------------------+---------------------------------------------------+
314 | Variable | Description |
315 +=======================+===================================================+
316 | `loop.index` | The current iteration of the loop. (1 indexed) |
317 +-----------------------+---------------------------------------------------+
318 | `loop.index0` | The current iteration of the loop. (0 indexed) |
319 +-----------------------+---------------------------------------------------+
320 | `loop.revindex` | The number of iterations from the end of the loop |
322 +-----------------------+---------------------------------------------------+
323 | `loop.revindex0` | The number of iterations from the end of the loop |
325 +-----------------------+---------------------------------------------------+
326 | `loop.first` | True if first iteration. |
327 +-----------------------+---------------------------------------------------+
328 | `loop.last` | True if last iteration. |
329 +-----------------------+---------------------------------------------------+
330 | `loop.length` | The number of items in the sequence. |
331 +-----------------------+---------------------------------------------------+
332 | `loop.cycle` | A helper function to cycle between a list of |
333 | | sequences. See the explanation below. |
334 +-----------------------+---------------------------------------------------+
336 Within a for-loop, it's psosible to cycle among a list of strings/variables
337 each time through the loop by using the special `loop.cycle` helper::
339 {% for row in rows %}
340 <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
345 Unlike in Python it's not possible to `break` or `continue` in a loop. You
346 can however filter the sequence during iteration which allows you to skip
347 items. The following example skips all the users which are hidden::
349 {% for user in users if not user.hidden %}
350 <li>{{ user.username|e }}</li>
353 The advantage is that the special `loop` variable will count correctly thus
354 not counting the users not iterated over.
356 If no iteration took place because the sequence was empty or the filtering
357 removed all the items from the sequence you can render a replacement block
361 {% for user in users %}
362 <li>{{ user.username|e }}</li>
364 <li><em>no users found</em></li>
372 The `if` statement in Jinja is comparable with the if statements of Python.
373 In the simplest form you can use it to test if a variable is defined, not
378 {% for user in users %}
379 <li>{{ user.username|e }}</li>
384 For multiple branches `elif` and `else` can be used like in Python. You can
385 use more complex :ref:`expressions` there too::
389 {% elif kenny.dead %}
390 You killed Kenny! You bastard!!!
392 Kenny looks okay --- so far
395 If can also be used as :ref:`inline expression <if-expression>` and for
396 :ref:`loop filtering <loop-filtering>`.
402 Macros comparable with functions in regular programming languages. They are
403 useful to put often used idoms into reusable functions to not repeat yourself.
405 Macros can be defined in helper templates with then are :ref:`imported <import>`
406 or directly in the template where they are used. There is one big difference
407 between those two possibilities. A macro that is defined in the template where
408 it's also used has access to the context passed to the template. A macro
409 defined in another template and then imported can only access variables defined
410 there or in the global context.
412 Here a small example of a macro that renders a form element::
414 {% macro input(name, value='', type='text', size=20) -%}
415 <input type="{{ type }}" name="{{ name }}" value="{{
416 value|e }}" size="{{ size }}">
419 The macro can then be called like a function in the namespace::
421 <p>{{ input('username') }}</p>
422 <p>{{ input('password', type='password') }}</p>
424 If the macro was defiend in a different template you have to
425 :ref:`import <import>` it first.
427 Inside macros you have access to three special variables:
430 If more positional arguments are passed to the macro then accepted by the
431 macro they end up in the special `varargs` variable as list of values.
434 Like `varargs` but for keyword arguments. All unconsumed keyword
435 arguments are stored in this special variable.
438 If the macro was called from a :ref:`call` tag the caller is stored in
439 this variable as macro which can be called.
441 Macros also expose some of their internal details. The following attributes
442 are available on a macro object:
445 The name of the macro. ``{{ input.name }}`` will print ``input``.
448 A tuple of the names of arguments the macro accepts.
451 A tuple of default values.
454 This is `true` if the macro accepts extra keyword arguments (ie: accesses
455 the special `kwargs` variable).
458 This is `true` if the macro accepts extra positional arguments (ie:
459 accesses the special `varargs` variable).
462 This is `true` if the macro accesses the special `caller` variable and may
463 be called from a :ref:`call` tag.
471 In some cases it can be useful to pass a macro to another macro. For this
472 purpose you can use the special `call` block. The following example shows
473 a macro that takes advantage of the call functionality and how it can be
476 {% macro render_dialog(title, class='dialog') -%}
477 <div class="{{ class }}">
479 <div class="contents">
485 {% call render_dialog('Hello World') %}
486 This is a simple dialog rendered by using a macro and
490 It's also possible to pass arguments back to the call block. This makes it
491 useful as replacement for loops. It is however not possible to call a
492 call block with another call block.
494 Here an example of how a call block can be used with arguments::
496 {% macro dump_users(users) -%}
498 {%- for user in users %}
499 <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
504 {% call(user) dump_users(list_of_user) %}
507 <dd>{{ user.realname|e }}</dd>
509 <dd>{{ user.description }}</dd>
517 Inside code blocks you can also assign values to variables. Assignments at
518 top level (outside of blocks, macros or loops) are exported from the template
519 like top level macros and can be imported by other templates.
521 Assignments are just written in code blocks like any other statement just
522 without explicit keyword::
524 {% navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
530 The `extends` tag can be used to extend a template from another one. You
531 can have multiple of them in a file but only one of them may be executed
532 at the time. There is no support for multiple inheritance. See the section
533 about :ref:`template-inheritance` above.
539 Blocks are used for inheritance and act as placeholders and replacements
540 at the same time. They are documented in detail as part of the section
541 about :ref:`template-inheritance`.
547 The `include` statement is useful to include a template and return the
548 rendered contents of that file into the current namespace::
550 {% include 'header.html' %}
552 {% include 'footer.html' %}
554 Included templates have access to the current template variables minus local
562 Jinja2 supports putting often used code into macros. These macros can go into
563 different templates and get imported from there. This works similar to the
564 import statements in Python. It's important to know that imports are cached
565 and imported templates don't have access to the current template variables,
568 There are two ways to import templates. You can import the complete template
569 into a variable or request specific macros / exported variables from it.
571 Imagine we have a helper module that renders forms (called `forms.html`)::
573 {% macro input(name, value='', type='text') -%}
574 <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
577 {%- macro textarea(name, value='', rows=10, cols=40) -%}
578 <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
579 }}">{{ value|e }}</textarea>
582 The easiest and most flexible is importing the whole module into a variable.
583 That way you can access the attributes::
585 {% import 'forms.html' as forms %}
588 <dd>{{ forms.input('username') }}</dd>
590 <dd>{{ forms.input('password', type='password') }}</dd>
592 <p>{{ forms.textarea('comment') }}</p>
595 Alternatively you can import names from the template into the current
598 {% from 'forms.html' import input as input_field, textarea %}
601 <dd>{{ input_field('username') }}</dd>
603 <dd>{{ input_field('password', type='password') }}</dd>
605 <p>{{ textarea('comment') }}</p>
613 Jinja allows basic expressions everywhere. These work very similar to regular
614 Python and even if you're not working with Python you should feel comfortable
620 The simplest form of expressions are literals. Literals are representations
621 for Python objects such as strings and numbers. The following literals exist:
624 Everything between two double or single quotes is a string. They are
625 useful whenever you need a string in the template (for example as
626 arguments to function calls, filters or just to extend or include a
630 Integers and floating point numbers are created by just writing the
631 number down. If a dot is present the number is a float, otherwise an
632 integer. Keep in mind that for Python ``42`` and ``42.0`` is something
635 ['list', 'of', 'objects']:
636 Everything between two brackets is a list. Lists are useful to store
637 sequential data in or to iterate over them. For example you can easily
638 create a list of links using lists and tuples with a for loop::
641 {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
642 ('downloads.html', 'Downloads')] %}
643 <li><a href="{{ href }}">{{ caption }}</a></li>
647 ('tuple', 'of', 'values'):
648 Tuples are like lists, just that you can't modify them. If the tuple
649 only has one item you have to end it with a comma. Tuples are usually
650 used to represent items of two or more elements. See the example above
653 {'dict': 'of', 'keys': 'and', 'value': 'pairs'}:
654 A dict in Python is a structure that combines keys and values. Keys must
655 be unique and always have exactly one value. Dicts are rarely used in
656 templates, they are useful in some rare cases such as the :func:`xmlattr`
660 true is always true and false is always false. Keep in mind that those
661 literals are lowercase!
666 Jinja allows you to calculate with values. This is rarely useful in templates
667 but exists for completeness sake. The following operators are supported:
670 Adds two objects with each other. Usually numbers but if both objects are
671 strings or lists you can concatenate them this way. This however is not
672 the preferred way to concatenate strings! For string concatenation have
673 a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``.
676 Substract two numbers from each other. ``{{ 3 - 2 }}`` is ``1``.
679 Divide two numbers. The return value will be a floating point number.
680 ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.
683 Divide two numbers and return the truncated integer result.
684 ``{{ 20 / 7 }}`` is ``2``.
687 Calculate the remainder of an integer division between the left and right
688 operand. ``{{ 11 % 7 }}`` is ``4``.
691 Multiply the left operand with the right one. ``{{ 2 * 2 }}`` would
692 return ``4``. This can also be used to repeat string multiple times.
693 ``{{ '=' * 80 }}`` would print a bar of 80 equal signs.
696 Raise the left operand to the power of the right operand. ``{{ 2**3 }}``
702 For `if` statements / `for` filtering or `if` expressions it can be useful to
703 combine group multiple expressions:
706 Return true if the left and the right operand is true.
709 Return true if the left or the right operand is true.
712 negate a statement (see below).
717 Note that there is no support for any bit operations or something similar.
719 - special note regarding ``not``: The ``is`` and ``in`` operators support
720 negation using an infix notation too: ``foo is not bar`` and
721 ``foo not in bar`` instead of ``not foo is bar`` and ``not foo in bar``.
722 All other expressions require a prefix notation: ``not (foo and bar).``
728 The following operators are very useful but don't fit into any of the other
732 Perform sequence / mapping containment test. Returns true if the left
733 operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for
737 Performs a :ref:`test <tests>`.
740 Applies a :ref:`filter <filters>`.
743 Converts all operands into strings and concatenates them.
744 ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is
745 ``'John'``) ``Hello John!``.
748 Call a callable: ``{{ post.render() }}``. Inside of the parentheses you
749 can use arguments and keyword arguments like in python:
750 ``{{ post.render(user, full=true) }}``.
753 Get an attribute of an object. (See :ref:`variables`)
761 It is also possible to use inline `if` expressions. These are useful in some
762 situations. For example you can use this to extend from one template if a
763 variable is defined, otherwise from the default layout template::
765 {% extends layout_template if layout_template is defined else 'master.html' %}
767 The general syntax is ``<do something> if <something is true> else <do
773 List of Builtin Filters
774 -----------------------
781 List of Builtin Tests
782 ---------------------
787 List of Global Functions
788 ------------------------
790 The following functions are available in the global scope by default:
792 .. function:: range([start,] stop[, step])
794 Return a list containing an arithmetic progression of integers.
795 range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
796 When step is given, it specifies the increment (or decrement).
797 For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
798 These are exactly the valid indices for a list of 4 elements.
800 This is useful to repeat a template block multiple times for example
801 to fill a list. Imagine you have 7 users in the list but you want to
802 render three empty items to enforce a height with CSS::
805 {% for user in users %}
806 <li>{{ user.username }}</li>
808 {% for number in range(10 - users|count) %}
809 <li class="empty"><span>...</span></li>
813 .. function:: lipsum(n=5, html=True, min=20, max=100)
815 Generates some lorem ipsum for the template. Per default five paragraphs
816 with HTML are generated each paragraph between 20 and 100 words. If html
817 is disabled regular text is returned. This is useful to generate simple
818 contents for layout testing.