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 "subscript" 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.
77 .. _notes-on-subscriptions:
79 .. admonition:: Implementation
81 For convenience sake ``foo.bar`` in Jinja2 does the following things on
84 - check if there is an attribute called `bar` on `foo`.
85 - if there is not, check if there is an item ``'bar'`` in `foo`.
86 - if there is not, return an undefined object.
88 ``foo['bar']`` on the other hand works mostly the same with the a small
89 difference in the order:
91 - check if there is an item ``'bar'`` in `foo`.
92 - if there is not, check if there is an attribute called `bar` on `foo`.
93 - if there is not, return an undefined object.
95 This is important if an object has an item or attribute with the same
96 name. Additionally there is the :func:`attr` filter that just looks up
104 Variables can by modified by **filters**. Filters are separated from the
105 variable by a pipe symbol (``|``) and may have optional arguments in
106 parentheses. Multiple filters can be chained. The output of one filter is
109 ``{{ name|striptags|title }}`` for example will remove all HTML Tags from the
110 `name` and title-cases it. Filters that accept arguments have parentheses
111 around the arguments, like a function call. This example will join a list
112 by spaces: ``{{ list|join(', ') }}``.
114 The :ref:`builtin-filters` below describes all the builtin filters.
121 Beside filters there are also so called "tests" available. Tests can be used
122 to test a variable against a common expression. To test a variable or
123 expression you add `is` plus the name of the test after the variable. For
124 example to find out if a variable is defined you can do ``name is defined``
125 which will then return true or false depending on if `name` is defined.
127 Tests can accept arguments too. If the test only takes one argument you can
128 leave out the parentheses to group them. For example the following two
129 expressions do the same::
131 {% if loop.index is divisibleby 3 %}
132 {% if loop.index is divisibleby(3) %}
134 The :ref:`builtin-tests` below describes all the builtin tests.
140 To comment-out part of a line in a template, use the comment syntax which is
141 by default set to ``{# ... #}``. This is useful to comment out parts of the
142 template for debugging or to add information for other template designers or
145 {# note: disabled template because we no longer user this
146 {% for user in users %}
155 In the default configuration whitespace is not further modified by the
156 template engine, so each whitespace (spaces, tabs, newlines etc.) is returned
157 unchanged. If the application configures Jinja to `trim_blocks` the first
158 newline after a a template tag is removed automatically (like in PHP).
160 But you can also strip whitespace in templates by hand. If you put an minus
161 sign (``-``) to the start or end of an block (for example a for tag), a
162 comment or variable expression you can remove the whitespaces after or before
165 {% for item in seq -%}
169 This will yield all elements without whitespace between them. If `seq` was
170 a list of numbers from ``1`` to ``9`` the output would be ``123456789``.
172 If :ref:`line-statements` are enabled they strip leading whitespace
173 automatically up to the beginning of the line.
177 You must not use a whitespace between the tag and the minus sign.
181 {%- if foo -%}...{% endif %}
185 {% - if foo - %}...{% endif %}
191 It is sometimes desirable or even necessary to have Jinja ignore parts it
192 would otherwise handle as variables or blocks. For example if the default
193 syntax is used and you want to use ``{{`` as raw string in the template and
194 not start a variable you have to use a trick.
196 The easiest way is to output the variable delimiter (``{{``) by using a
197 variable expression::
201 For bigger sections it makes sense to mark a block `raw`. For example to
202 put Jinja syntax as example into a template you can use this snippet::
206 {% for item in seq %}
218 If line statements are enabled by the application it's possible to mark a
219 line as a statement. For example if the line statement prefix is configured
220 to ``#`` the following two examples are equivalent::
229 {% for item in seq %}
234 The line statement prefix can appear anywhere on the line as long as no text
235 precedes it. For better readability statements that start a block (such as
236 `for`, `if`, `elif` etc.) may end with a colon::
245 Line statements can span multiple lines if there are open parentheses,
249 # for href, caption in [('index.html', 'Index'),
250 ('about.html', 'About')]:
251 <li><a href="{{ href }}">{{ caption }}</a></li>
256 .. _template-inheritance:
261 The most powerful part of Jinja is template inheritance. Template inheritance
262 allows you to build a base "skeleton" template that contains all the common
263 elements of your site and defines **blocks** that child templates can override.
265 Sounds complicated but is very basic. It's easiest to understand it by starting
272 This template, which we'll call ``base.html``, defines a simple HTML skeleton
273 document that you might use for a simple two-column page. It's the job of
274 "child" templates to fill the empty blocks with content::
276 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
278 <html xmlns="http://www.w3.org/1999/xhtml">
281 <link rel="stylesheet" href="style.css" />
282 <title>{% block title %}{% endblock %} - My Webpage</title>
286 <div id="content">{% block content %}{% endblock %}</div>
289 © Copyright 2008 by <a href="http://domain.invalid/">you</a>.
294 In this example, the ``{% block %}`` tags define four blocks that child templates
295 can fill in. All the `block` tag does is to tell the template engine that a
296 child template may override those portions of the template.
301 A child template might look like this::
303 {% extends "base.html" %}
304 {% block title %}Index{% endblock %}
307 <style type="text/css">
308 .important { color: #336699; }
313 <p class="important">
314 Welcome on my awsome homepage.
318 The ``{% extends %}`` tag is the key here. It tells the template engine that
319 this template "extends" another template. When the template system evaluates
320 this template, first it locates the parent. The extends tag should be the
321 first tag in the template. Everything before it is printed out normally and
322 may cause confusion. For details about this behavior and how to take
323 advantage of it, see :ref:`null-master-fallback`.
325 The filename of the template depends on the template loader. For example the
326 :class:`FileSystemLoader` allows you to access other templates by giving the
327 filename. You can access templates in subdirectories with an slash::
329 {% extends "layout/default.html" %}
331 But this behavior can depend on the application embedding Jinja. Note that
332 since the child template doesn't define the ``footer`` block, the value from
333 the parent template is used instead.
335 You can't define multiple ``{% block %}`` tags with the same name in the
336 same template. This limitation exists because a block tag works in "both"
337 directions. That is, a block tag doesn't just provide a hole to fill - it
338 also defines the content that fills the hole in the *parent*. If there
339 were two similarly-named ``{% block %}`` tags in a template, that template's
340 parent wouldn't know which one of the blocks' content to use.
342 If you want to print a block multiple times you can however use the special
343 `self` variable and call the block with that name::
345 <title>{% block title %}{% endblock %}</title>
346 <h1>{{ self.title() }}</h1>
347 {% block body %}{% endblock %}
349 Unlike Python Jinja does not support multiple inheritance. So you can only have
350 one extends tag called per rendering.
356 It's possible to render the contents of the parent block by calling `super`.
357 This gives back the results of the parent block::
360 <h3>Table Of Contents</h3>
369 Jinja2 allows you to put the name of the block after the end tag for better
373 {% block inner_sidebar %}
375 {% endblock inner_sidebar %}
376 {% endblock sidebar %}
378 However the name after the `endblock` word must match the block name.
384 When generating HTML from templates, there's always a risk that a variable will
385 include characters that affect the resulting HTML. There are two approaches:
386 manually escaping each variable or automatically escaping everything by default.
388 Jinja supports both, but what is used depends on the application configuration.
389 The default configuaration is no automatic escaping for various reasons:
391 - escaping everything except of safe values will also mean that Jinja is
392 escaping variables known to not include HTML such as numbers which is
393 a huge performance hit.
395 - The information about the safety of a variable is very fragile. It could
396 happen that by coercing safe and unsafe values the return value is double
399 Working with Manual Escaping
400 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
402 If manual escaping is enabled it's **your** responsibility to escape
403 variables if needed. What to escape? If you have a variable that *may*
404 include any of the following chars (``>``, ``<``, ``&``, or ``"``) you
405 **have to** escape it unless the variable contains well-formed and trusted
406 HTML. Escaping works by piping the variable through the ``|e`` filter:
407 ``{{ user.username|e }}``.
409 Working with Automatic Escaping
410 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
412 When automatic escaping is enabled everything is escaped by default except
413 for values explicitly marked as safe. Those can either be marked by the
414 application or in the template by using the `|safe` filter. The main
415 problem with this approach is that Python itself doesn't have the concept
416 of tainted values so the information if a value is safe or unsafe can get
417 lost. If the information is lost escaping will take place which means that
418 you could end up with double escaped contents.
420 Double escaping is easy to avoid however, just rely on the tools Jinja2
421 provides and don't use builtin Python constructs such as the string modulo
424 Functions returning template data (macros, `super`, `self.BLOCKNAME`) return
427 String literals in templates with automatic escaping are considered unsafe
428 too. The reason for this is that the safe string is an extension to Python
429 and not every library will work properly with it.
432 List of Control Structures
433 --------------------------
435 A control structure refers to all those things that control the flow of a
436 program - conditionals (i.e. if/elif/else), for-loops, as well as things like
437 macros and blocks. Control structures appear inside ``{% ... %}`` blocks
438 in the default syntax.
443 Loop over each item in a sequence. For example, to display a list of users
444 provided in a variable called `users`::
448 {% for user in users %}
449 <li>{{ user.username|e }}</li>
453 Inside of a for loop block you can access some special variables:
455 +-----------------------+---------------------------------------------------+
456 | Variable | Description |
457 +=======================+===================================================+
458 | `loop.index` | The current iteration of the loop. (1 indexed) |
459 +-----------------------+---------------------------------------------------+
460 | `loop.index0` | The current iteration of the loop. (0 indexed) |
461 +-----------------------+---------------------------------------------------+
462 | `loop.revindex` | The number of iterations from the end of the loop |
464 +-----------------------+---------------------------------------------------+
465 | `loop.revindex0` | The number of iterations from the end of the loop |
467 +-----------------------+---------------------------------------------------+
468 | `loop.first` | True if first iteration. |
469 +-----------------------+---------------------------------------------------+
470 | `loop.last` | True if last iteration. |
471 +-----------------------+---------------------------------------------------+
472 | `loop.length` | The number of items in the sequence. |
473 +-----------------------+---------------------------------------------------+
474 | `loop.cycle` | A helper function to cycle between a list of |
475 | | sequences. See the explanation below. |
476 +-----------------------+---------------------------------------------------+
478 Within a for-loop, it's possible to cycle among a list of strings/variables
479 each time through the loop by using the special `loop.cycle` helper::
481 {% for row in rows %}
482 <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
487 Unlike in Python it's not possible to `break` or `continue` in a loop. You
488 can however filter the sequence during iteration which allows you to skip
489 items. The following example skips all the users which are hidden::
491 {% for user in users if not user.hidden %}
492 <li>{{ user.username|e }}</li>
495 The advantage is that the special `loop` variable will count correctly thus
496 not counting the users not iterated over.
498 If no iteration took place because the sequence was empty or the filtering
499 removed all the items from the sequence you can render a replacement block
503 {% for user in users %}
504 <li>{{ user.username|e }}</li>
506 <li><em>no users found</em></li>
510 It is also possible to use loops recursively. This is useful if you are
511 dealing with recursive data such as sitemaps. To use loops recursively you
512 basically have to add the `recursive` modifier to the loop definition and
513 call the `loop` variable with the new iterable where you want to recurse.
515 The following example implements a sitemap with recursive loops::
518 {%- for item in sitemap recursive %}
519 <li><a href="{{ item.href|e }}">{{ item.title }}</a>
520 {%- if item.children -%}
521 <ul class="submenu">{{ loop(item.children) }}</ul>
530 The `if` statement in Jinja is comparable with the if statements of Python.
531 In the simplest form you can use it to test if a variable is defined, not
536 {% for user in users %}
537 <li>{{ user.username|e }}</li>
542 For multiple branches `elif` and `else` can be used like in Python. You can
543 use more complex :ref:`expressions` there too::
547 {% elif kenny.dead %}
548 You killed Kenny! You bastard!!!
550 Kenny looks okay --- so far
553 If can also be used as :ref:`inline expression <if-expression>` and for
554 :ref:`loop filtering <loop-filtering>`.
560 Macros are comparable with functions in regular programming languages. They
561 are useful to put often used idioms into reusable functions to not repeat
564 Here a small example of a macro that renders a form element::
566 {% macro input(name, value='', type='text', size=20) -%}
567 <input type="{{ type }}" name="{{ name }}" value="{{
568 value|e }}" size="{{ size }}">
571 The macro can then be called like a function in the namespace::
573 <p>{{ input('username') }}</p>
574 <p>{{ input('password', type='password') }}</p>
576 If the macro was defined in a different template you have to
577 :ref:`import <import>` it first.
579 Inside macros you have access to three special variables:
582 If more positional arguments are passed to the macro than accepted by the
583 macro they end up in the special `varargs` variable as list of values.
586 Like `varargs` but for keyword arguments. All unconsumed keyword
587 arguments are stored in this special variable.
590 If the macro was called from a :ref:`call<call>` tag the caller is stored
591 in this variable as macro which can be called.
593 Macros also expose some of their internal details. The following attributes
594 are available on a macro object:
597 The name of the macro. ``{{ input.name }}`` will print ``input``.
600 A tuple of the names of arguments the macro accepts.
603 A tuple of default values.
606 This is `true` if the macro accepts extra keyword arguments (ie: accesses
607 the special `kwargs` variable).
610 This is `true` if the macro accepts extra positional arguments (ie:
611 accesses the special `varargs` variable).
614 This is `true` if the macro accesses the special `caller` variable and may
615 be called from a :ref:`call<call>` tag.
617 If a macro name starts with an underscore it's not exported and can't
626 In some cases it can be useful to pass a macro to another macro. For this
627 purpose you can use the special `call` block. The following example shows
628 a macro that takes advantage of the call functionality and how it can be
631 {% macro render_dialog(title, class='dialog') -%}
632 <div class="{{ class }}">
634 <div class="contents">
640 {% call render_dialog('Hello World') %}
641 This is a simple dialog rendered by using a macro and
645 It's also possible to pass arguments back to the call block. This makes it
646 useful as replacement for loops. Generally speaking a call block works
647 exactly like an macro, just that it doesn't have a name.
649 Here an example of how a call block can be used with arguments::
651 {% macro dump_users(users) -%}
653 {%- for user in users %}
654 <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
659 {% call(user) dump_users(list_of_user) %}
662 <dd>{{ user.realname|e }}</dd>
664 <dd>{{ user.description }}</dd>
672 Filter sections allow you to apply regular Jinja2 filters on a block of
673 template data. Just wrap the code in the special `filter` section::
676 This text becomes uppercase
683 Inside code blocks you can also assign values to variables. Assignments at
684 top level (outside of blocks, macros or loops) are exported from the template
685 like top level macros and can be imported by other templates.
687 Assignments use the `set` tag and can have multiple targets::
689 {% set navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
690 {% set key, value = call_something() %}
696 The `extends` tag can be used to extend a template from another one. You
697 can have multiple of them in a file but only one of them may be executed
698 at the time. There is no support for multiple inheritance. See the section
699 about :ref:`template-inheritance` above.
705 Blocks are used for inheritance and act as placeholders and replacements
706 at the same time. They are documented in detail as part of the section
707 about :ref:`template-inheritance`.
713 The `include` statement is useful to include a template and return the
714 rendered contents of that file into the current namespace::
716 {% include 'header.html' %}
718 {% include 'footer.html' %}
720 Included templates have access to the variables of the active context by
721 default. For more details about context behavior of imports and includes
722 see :ref:`import-visibility`.
729 Jinja2 supports putting often used code into macros. These macros can go into
730 different templates and get imported from there. This works similar to the
731 import statements in Python. It's important to know that imports are cached
732 and imported templates don't have access to the current template variables,
733 just the globals by defualt. For more details about context behavior of
734 imports and includes see :ref:`import-visibility`.
736 There are two ways to import templates. You can import the complete template
737 into a variable or request specific macros / exported variables from it.
739 Imagine we have a helper module that renders forms (called `forms.html`)::
741 {% macro input(name, value='', type='text') -%}
742 <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
745 {%- macro textarea(name, value='', rows=10, cols=40) -%}
746 <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
747 }}">{{ value|e }}</textarea>
750 The easiest and most flexible is importing the whole module into a variable.
751 That way you can access the attributes::
753 {% import 'forms.html' as forms %}
756 <dd>{{ forms.input('username') }}</dd>
758 <dd>{{ forms.input('password', type='password') }}</dd>
760 <p>{{ forms.textarea('comment') }}</p>
763 Alternatively you can import names from the template into the current
766 {% from 'forms.html' import input as input_field, textarea %}
769 <dd>{{ input_field('username') }}</dd>
771 <dd>{{ input_field('password', type='password') }}</dd>
773 <p>{{ textarea('comment') }}</p>
775 Macros and variables starting with one ore more underscores are private and
779 .. _import-visibility:
781 Import Context Behavior
782 -----------------------
784 Per default included templates are passed the current context and imported
785 templates not. The reason for this is that imports unlike includes are
786 cached as imports are often used just as a module that holds macros.
788 This however can be changed of course explicitly. By adding `with context`
789 or `without context` to the import/include directive the current context
790 can be passed to the template and caching is disabled automatically.
794 {% from 'forms.html' import input with context %}
795 {% include 'header.html' without context %}
799 In Jinja 2.0 the context that was passed to the included template
800 did not include variables define in the template. As a matter of
801 fact this did not work::
803 {% for box in boxes %}
804 {% include "render_box.html" %}
807 The included template ``render_box.html`` is not able to access
808 `box` in Jinja 2.0, but in Jinja 2.1.
816 Jinja allows basic expressions everywhere. These work very similar to regular
817 Python and even if you're not working with Python you should feel comfortable
823 The simplest form of expressions are literals. Literals are representations
824 for Python objects such as strings and numbers. The following literals exist:
827 Everything between two double or single quotes is a string. They are
828 useful whenever you need a string in the template (for example as
829 arguments to function calls, filters or just to extend or include a
833 Integers and floating point numbers are created by just writing the
834 number down. If a dot is present the number is a float, otherwise an
835 integer. Keep in mind that for Python ``42`` and ``42.0`` is something
838 ['list', 'of', 'objects']:
839 Everything between two brackets is a list. Lists are useful to store
840 sequential data in or to iterate over them. For example you can easily
841 create a list of links using lists and tuples with a for loop::
844 {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
845 ('downloads.html', 'Downloads')] %}
846 <li><a href="{{ href }}">{{ caption }}</a></li>
850 ('tuple', 'of', 'values'):
851 Tuples are like lists, just that you can't modify them. If the tuple
852 only has one item you have to end it with a comma. Tuples are usually
853 used to represent items of two or more elements. See the example above
856 {'dict': 'of', 'key': 'and', 'value': 'pairs'}:
857 A dict in Python is a structure that combines keys and values. Keys must
858 be unique and always have exactly one value. Dicts are rarely used in
859 templates, they are useful in some rare cases such as the :func:`xmlattr`
863 true is always true and false is always false.
867 The special constants `true`, `false` and `none` are indeed lowercase.
868 Because that caused confusion in the past, when writing `True` expands
869 to an undefined variable that is considered false, all three of them can
870 be written in title case too (`True`, `False`, and `None`). However for
871 consistency (all Jinja identifiers are lowercase) you should use the
877 Jinja allows you to calculate with values. This is rarely useful in templates
878 but exists for completeness sake. The following operators are supported:
881 Adds two objects with each other. Usually numbers but if both objects are
882 strings or lists you can concatenate them this way. This however is not
883 the preferred way to concatenate strings! For string concatenation have
884 a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``.
887 Substract two numbers from each other. ``{{ 3 - 2 }}`` is ``1``.
890 Divide two numbers. The return value will be a floating point number.
891 ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.
894 Divide two numbers and return the truncated integer result.
895 ``{{ 20 / 7 }}`` is ``2``.
898 Calculate the remainder of an integer division between the left and right
899 operand. ``{{ 11 % 7 }}`` is ``4``.
902 Multiply the left operand with the right one. ``{{ 2 * 2 }}`` would
903 return ``4``. This can also be used to repeat string multiple times.
904 ``{{ '=' * 80 }}`` would print a bar of 80 equal signs.
907 Raise the left operand to the power of the right operand. ``{{ 2**3 }}``
913 For `if` statements / `for` filtering or `if` expressions it can be useful to
914 combine group multiple expressions:
917 Return true if the left and the right operand is true.
920 Return true if the left or the right operand is true.
923 negate a statement (see below).
930 The ``is`` and ``in`` operators support negation using an infix notation
931 too: ``foo is not bar`` and ``foo not in bar`` instead of ``not foo is bar``
932 and ``not foo in bar``. All other expressions require a prefix notation:
933 ``not (foo and bar).``
939 The following operators are very useful but don't fit into any of the other
943 Perform sequence / mapping containment test. Returns true if the left
944 operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for
948 Performs a :ref:`test <tests>`.
951 Applies a :ref:`filter <filters>`.
954 Converts all operands into strings and concatenates them.
955 ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is
956 ``'John'``) ``Hello John!``.
959 Call a callable: ``{{ post.render() }}``. Inside of the parentheses you
960 can use arguments and keyword arguments like in python:
961 ``{{ post.render(user, full=true) }}``.
964 Get an attribute of an object. (See :ref:`variables`)
972 It is also possible to use inline `if` expressions. These are useful in some
973 situations. For example you can use this to extend from one template if a
974 variable is defined, otherwise from the default layout template::
976 {% extends layout_template if layout_template is defined else 'master.html' %}
978 The general syntax is ``<do something> if <something is true> else <do
981 The `else` part is optional. If not provided the else block implicitly
982 evaluates into an undefined object::
984 {{ '[%s]' % page.title if page.title }}
989 List of Builtin Filters
990 -----------------------
997 List of Builtin Tests
998 ---------------------
1003 List of Global Functions
1004 ------------------------
1006 The following functions are available in the global scope by default:
1008 .. function:: range([start,] stop[, step])
1010 Return a list containing an arithmetic progression of integers.
1011 range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
1012 When step is given, it specifies the increment (or decrement).
1013 For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
1014 These are exactly the valid indices for a list of 4 elements.
1016 This is useful to repeat a template block multiple times for example
1017 to fill a list. Imagine you have 7 users in the list but you want to
1018 render three empty items to enforce a height with CSS::
1021 {% for user in users %}
1022 <li>{{ user.username }}</li>
1024 {% for number in range(10 - users|count) %}
1025 <li class="empty"><span>...</span></li>
1029 .. function:: lipsum(n=5, html=True, min=20, max=100)
1031 Generates some lorem ipsum for the template. Per default five paragraphs
1032 with HTML are generated each paragraph between 20 and 100 words. If html
1033 is disabled regular text is returned. This is useful to generate simple
1034 contents for layout testing.
1036 .. function:: dict(\**items)
1038 A convenient alternative to dict literals. ``{'foo': 'bar'}`` is the same
1039 as ``dict(foo='bar')``.
1045 The following sections cover the built-in Jinja2 extensions that may be
1046 enabled by the application. The application could also provide further
1047 extensions not covered by this documentation. In that case there should
1048 be a separate document explaining the extensions.
1050 .. _i18n-in-templates:
1055 If the i18n extension is enabled it's possible to mark parts in the template
1056 as translatable. To mark a section as translatable you can use `trans`::
1058 <p>{% trans %}Hello {{ user }}!{% endtrans %}</p>
1060 To translate a template expression --- say, using template filters or just
1061 accessing an attribute of an object --- you need to bind the expression to a
1062 name for use within the translation block::
1064 <p>{% trans user=user.username %}Hello {{ user }}!{% endtrans %}</p>
1066 If you need to bind more than one expression inside a `trans` tag, separate
1067 the pieces with a comma (``,``)::
1069 {% trans book_title=book.title, author=author.name %}
1070 This is {{ book_title }} by {{ author }}
1073 Inside trans tags no statements are allowed, only variable tags are.
1075 To pluralize, specify both the singular and plural forms with the `pluralize`
1076 tag, which appears between `trans` and `endtrans`::
1078 {% trans count=list|length %}
1079 There is {{ count }} {{ name }} object.
1081 There are {{ count }} {{ name }} objects.
1084 Per default the first variable in a block is used to determine the correct
1085 singular or plural form. If that doesn't work out you can specify the name
1086 which should be used for pluralizing by adding it as parameter to `pluralize`::
1088 {% trans ..., user_count=users|length %}...
1089 {% pluralize user_count %}...{% endtrans %}
1091 It's also possible to translate strings in expressions. For that purpose
1092 three functions exist:
1094 _ `gettext`: translate a single string
1095 - `ngettext`: translate a pluralizable string
1096 - `_`: alias for `gettext`
1098 For example you can print a translated string easily this way::
1100 {{ _('Hello World!') }}
1102 To use placeholders you can use the `format` filter::
1104 {{ _('Hello %(user)s!')|format(user=user.username) }}
1106 {{ _('Hello %s')|format(user.username) }}
1108 For multiple placeholders always use keyword arguments to `format` as other
1109 languages may not use the words in the same order.
1112 Expression Statement
1113 ~~~~~~~~~~~~~~~~~~~~
1115 If the expression-statement extension is loaded a tag called `do` is available
1116 that works exactly like the regular variable expression (``{{ ... }}``) just
1117 that it doesn't print anything. This can be used to modify lists::
1119 {% do navigation.append('a string') %}
1125 If the application enables the :ref:`loopcontrols-extension` it's possible to
1126 use `break` and `continue` in loops. When `break` is reached, the loop is
1127 terminated, if `continue` is eached the processing is stopped and continues
1128 with the next iteration.
1130 Here a loop that skips every second item::
1132 {% for user in users %}
1133 {%- if loop.index is even %}{% continue %}{% endif %}
1137 Likewise a look that stops processing after the 10th iteration::
1139 {% for user in users %}
1140 {%- if loop.index >= 10 %}{% break %}{% endif %}
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