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 depending 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 describes 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 %}
133 In the default configuration whitespace is not further modified by the
134 template engine, so each whitespace (spaces, tabs, newlines etc.) is returned
135 unchanged. If the application configures Jinja to `trim_blocks` the first
136 newline after a a template tag is removed automatically (like in PHP).
138 But you can also strip whitespace in templates by hand. If you put an minus
139 sign (``-``) to the start or end of an block (for example a for tag), a
140 comment or variable expression you can remove the whitespaces after or before
143 {% for item in seq -%}
147 This will yield all elements without whitespace between them. If `seq` was
148 a list of numbers from ``1`` to ``9`` the output would be ``123456789``.
150 If :ref:`line-statements` are enabled they strip leading whitespace
151 automatically up to the beginning of the line.
155 You must not use a whitespace between the tag and the minus sign.
159 {%- if foo -%}...{% endif %}
163 {% - if foo - %}...{% endif %}
169 It is sometimes desirable or even necessary to have Jinja ignore parts it
170 would otherwise handle as variables or blocks. For example if the default
171 syntax is used and you want to use ``{{`` as raw string in the template and
172 not start a variable you have to use a trick.
174 The easiest way is to output the variable delimiter (``{{``) by using a
175 variable expression::
179 For bigger sections it makes sense to mark a block `raw`. For example to
180 put Jinja syntax as example into a template you can use this snippet::
184 {% for item in seq %}
196 If line statements are enabled by the application it's possible to mark a
197 line as a statement. For example if the line statement prefix is configured
198 to ``#`` the following two examples are equivalent::
207 {% for item in seq %}
212 The line statement prefix can appear anywhere on the line as long as no text
213 precedes it. For better readability statements that start a block (such as
214 `for`, `if`, `elif` etc.) may end with a colon::
223 Line statements can span multiple lines if there are open parentheses,
227 # for href, caption in [('index.html', 'Index'),
228 ('about.html', 'About')]:
229 <li><a href="{{ href }}">{{ caption }}</a></li>
234 .. _template-inheritance:
239 The most powerful part of Jinja is template inheritance. Template inheritance
240 allows you to build a base "skeleton" template that contains all the common
241 elements of your site and defines **blocks** that child templates can override.
243 Sounds complicated but is very basic. It's easiest to understand it by starting
250 This template, which we'll call ``base.html``, defines a simple HTML skeleton
251 document that you might use for a simple two-column page. It's the job of
252 "child" templates to fill the empty blocks with content::
254 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
256 <html xmlns="http://www.w3.org/1999/xhtml">
259 <link rel="stylesheet" href="style.css" />
260 <title>{% block title %}{% endblock %} - My Webpage</title>
264 <div id="content">{% block content %}{% endblock %}</div>
267 © Copyright 2008 by <a href="http://domain.invalid/">you</a>.
272 In this example, the ``{% block %}`` tags define four blocks that child templates
273 can fill in. All the `block` tag does is to tell the template engine that a
274 child template may override those portions of the template.
279 A child template might look like this::
281 {% extends "base.html" %}
282 {% block title %}Index{% endblock %}
285 <style type="text/css">
286 .important { color: #336699; }
291 <p class="important">
292 Welcome on my awsome homepage.
296 The ``{% extends %}`` tag is the key here. It tells the template engine that
297 this template "extends" another template. When the template system evaluates
298 this template, first it locates the parent. The extends tag should be the
299 first tag in the template. Everything before it is printed out normally and
300 may cause confusion. For details about this behavior and how to take
301 advantage of it, see :ref:`null-master-fallback`.
303 The filename of the template depends on the template loader. For example the
304 :class:`FileSystemLoader` allows you to access other templates by giving the
305 filename. You can access templates in subdirectories with an slash::
307 {% extends "layout/default.html" %}
309 But this behavior can depend on the application embedding Jinja. Note that
310 since the child template doesn't define the ``footer`` block, the value from
311 the parent template is used instead.
313 You can't define multiple ``{% block %}`` tags with the same name in the
314 same template. This limitation exists because a block tag works in "both"
315 directions. That is, a block tag doesn't just provide a hole to fill - it
316 also defines the content that fills the hole in the *parent*. If there
317 were two similarly-named ``{% block %}`` tags in a template, that template's
318 parent wouldn't know which one of the blocks' content to use.
320 If you want to print a block multiple times you can however use the special
321 `self` variable and call the block with that name::
323 <title>{% block title %}{% endblock %}</title>
324 <h1>{{ self.title() }}</h1>
325 {% block body %}{% endblock %}
328 Unlike Python Jinja does not support multiple inheritance. So you can only have
329 one extends tag called per rendering.
335 It's possible to render the contents of the parent block by calling `super`.
336 This gives back the results of the parent block::
339 <h3>Table Of Contents</h3>
348 Jinja2 allows you to put the name of the block after the end tag for better
352 {% block inner_sidebar %}
354 {% endblock inner_sidebar %}
355 {% endblock sidebar %}
357 However the name after the `endblock` word must match the block name.
363 When generating HTML from templates, there's always a risk that a variable will
364 include characters that affect the resulting HTML. There are two approaches:
365 manually escaping each variable or automatically escaping everything by default.
367 Jinja supports both, but what is used depends on the application configuration.
368 The default configuaration is no automatic escaping for various reasons:
370 - escaping everything except of safe values will also mean that Jinja is
371 escaping variables known to not include HTML such as numbers which is
372 a huge performance hit.
374 - The information about the safety of a variable is very fragile. It could
375 happen that by coercing safe and unsafe values the return value is double
378 Working with Manual Escaping
379 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
381 If manual escaping is enabled it's **your** responsibility to escape
382 variables if needed. What to escape? If you have a variable that *may*
383 include any of the following chars (``>``, ``<``, ``&``, or ``"``) you
384 **have to** escape it unless the variable contains well-formed and trusted
385 HTML. Escaping works by piping the variable through the ``|e`` filter:
386 ``{{ user.username|e }}``.
388 Working with Automatic Escaping
389 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
391 When automatic escaping is enabled everything is escaped by default except
392 for values explicitly marked as safe. Those can either be marked by the
393 application or in the template by using the `|safe` filter. The main
394 problem with this approach is that Python itself doesn't have the concept
395 of tainted values so the information if a value is safe or unsafe can get
396 lost. If the information is lost escaping will take place which means that
397 you could end up with double escaped contents.
399 Double escaping is easy to avoid however, just rely on the tools Jinja2
400 provides and don't use builtin Python constructs such as the string modulo
403 Functions returning template data (macros, `super`, `self.BLOCKNAME`) return
406 String literals in templates with automatic escaping are considered unsafe
407 too. The reason for this is that the safe string is an extension to Python
408 and not every library will work properly with it.
411 List of Control Structures
412 --------------------------
414 A control structure refers to all those things that control the flow of a
415 program - conditionals (i.e. if/elif/else), for-loops, as well as things like
416 macros and blocks. Control structures appear inside ``{% ... %}`` blocks
417 in the default syntax.
422 Loop over each item in a sequence. For example, to display a list of users
423 provided in a variable called `users`::
427 {% for user in users %}
428 <li>{{ user.username|e }}</li>
432 Inside of a for loop block you can access some special variables:
434 +-----------------------+---------------------------------------------------+
435 | Variable | Description |
436 +=======================+===================================================+
437 | `loop.index` | The current iteration of the loop. (1 indexed) |
438 +-----------------------+---------------------------------------------------+
439 | `loop.index0` | The current iteration of the loop. (0 indexed) |
440 +-----------------------+---------------------------------------------------+
441 | `loop.revindex` | The number of iterations from the end of the loop |
443 +-----------------------+---------------------------------------------------+
444 | `loop.revindex0` | The number of iterations from the end of the loop |
446 +-----------------------+---------------------------------------------------+
447 | `loop.first` | True if first iteration. |
448 +-----------------------+---------------------------------------------------+
449 | `loop.last` | True if last iteration. |
450 +-----------------------+---------------------------------------------------+
451 | `loop.length` | The number of items in the sequence. |
452 +-----------------------+---------------------------------------------------+
453 | `loop.cycle` | A helper function to cycle between a list of |
454 | | sequences. See the explanation below. |
455 +-----------------------+---------------------------------------------------+
457 Within a for-loop, it's possible to cycle among a list of strings/variables
458 each time through the loop by using the special `loop.cycle` helper::
460 {% for row in rows %}
461 <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
466 Unlike in Python it's not possible to `break` or `continue` in a loop. You
467 can however filter the sequence during iteration which allows you to skip
468 items. The following example skips all the users which are hidden::
470 {% for user in users if not user.hidden %}
471 <li>{{ user.username|e }}</li>
474 The advantage is that the special `loop` variable will count correctly thus
475 not counting the users not iterated over.
477 If no iteration took place because the sequence was empty or the filtering
478 removed all the items from the sequence you can render a replacement block
482 {% for user in users %}
483 <li>{{ user.username|e }}</li>
485 <li><em>no users found</em></li>
489 It is also possible to use loops recursively. This is useful if you are
490 dealing with recursive data such as sitemaps. To use loops recursively you
491 basically have to add the `recursive` modifier to the loop definition and
492 call the `loop` variable with the new iterable where you want to recurse.
494 The following example implements a sitemap with recursive loops::
497 {%- for item in sitemap recursive %}
498 <li><a href="{{ item.href|e }}">{{ item.title }}</a>
499 {%- if item.children -%}
500 <ul class="submenu">{{ loop(item.children) }}</ul>
509 The `if` statement in Jinja is comparable with the if statements of Python.
510 In the simplest form you can use it to test if a variable is defined, not
515 {% for user in users %}
516 <li>{{ user.username|e }}</li>
521 For multiple branches `elif` and `else` can be used like in Python. You can
522 use more complex :ref:`expressions` there too::
526 {% elif kenny.dead %}
527 You killed Kenny! You bastard!!!
529 Kenny looks okay --- so far
532 If can also be used as :ref:`inline expression <if-expression>` and for
533 :ref:`loop filtering <loop-filtering>`.
539 Macros are comparable with functions in regular programming languages. They
540 are useful to put often used idioms into reusable functions to not repeat
543 Here a small example of a macro that renders a form element::
545 {% macro input(name, value='', type='text', size=20) -%}
546 <input type="{{ type }}" name="{{ name }}" value="{{
547 value|e }}" size="{{ size }}">
550 The macro can then be called like a function in the namespace::
552 <p>{{ input('username') }}</p>
553 <p>{{ input('password', type='password') }}</p>
555 If the macro was defined in a different template you have to
556 :ref:`import <import>` it first.
558 Inside macros you have access to three special variables:
561 If more positional arguments are passed to the macro than accepted by the
562 macro they end up in the special `varargs` variable as list of values.
565 Like `varargs` but for keyword arguments. All unconsumed keyword
566 arguments are stored in this special variable.
569 If the macro was called from a :ref:`call<call>` tag the caller is stored
570 in this variable as macro which can be called.
572 Macros also expose some of their internal details. The following attributes
573 are available on a macro object:
576 The name of the macro. ``{{ input.name }}`` will print ``input``.
579 A tuple of the names of arguments the macro accepts.
582 A tuple of default values.
585 This is `true` if the macro accepts extra keyword arguments (ie: accesses
586 the special `kwargs` variable).
589 This is `true` if the macro accepts extra positional arguments (ie:
590 accesses the special `varargs` variable).
593 This is `true` if the macro accesses the special `caller` variable and may
594 be called from a :ref:`call<call>` tag.
602 In some cases it can be useful to pass a macro to another macro. For this
603 purpose you can use the special `call` block. The following example shows
604 a macro that takes advantage of the call functionality and how it can be
607 {% macro render_dialog(title, class='dialog') -%}
608 <div class="{{ class }}">
610 <div class="contents">
616 {% call render_dialog('Hello World') %}
617 This is a simple dialog rendered by using a macro and
621 It's also possible to pass arguments back to the call block. This makes it
622 useful as replacement for loops. Generally speaking a call block works
623 exactly like an macro, just that it doesn't have a name.
625 Here an example of how a call block can be used with arguments::
627 {% macro dump_users(users) -%}
629 {%- for user in users %}
630 <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
635 {% call(user) dump_users(list_of_user) %}
638 <dd>{{ user.realname|e }}</dd>
640 <dd>{{ user.description }}</dd>
648 Inside code blocks you can also assign values to variables. Assignments at
649 top level (outside of blocks, macros or loops) are exported from the template
650 like top level macros and can be imported by other templates.
652 Assignments use the `set` tag and can have multiple targets::
654 {% set navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
655 {% set key, value = call_something() %}
661 The `extends` tag can be used to extend a template from another one. You
662 can have multiple of them in a file but only one of them may be executed
663 at the time. There is no support for multiple inheritance. See the section
664 about :ref:`template-inheritance` above.
670 Blocks are used for inheritance and act as placeholders and replacements
671 at the same time. They are documented in detail as part of the section
672 about :ref:`template-inheritance`.
678 The `include` statement is useful to include a template and return the
679 rendered contents of that file into the current namespace::
681 {% include 'header.html' %}
683 {% include 'footer.html' %}
685 Included templates have access to the variables of the active context by
686 default. For more details about context behavior of imports and includes
687 see :ref:`import-visibility`.
694 Jinja2 supports putting often used code into macros. These macros can go into
695 different templates and get imported from there. This works similar to the
696 import statements in Python. It's important to know that imports are cached
697 and imported templates don't have access to the current template variables,
698 just the globals by defualt. For more details about context behavior of
699 imports and includes see :ref:`import-visibility`.
701 There are two ways to import templates. You can import the complete template
702 into a variable or request specific macros / exported variables from it.
704 Imagine we have a helper module that renders forms (called `forms.html`)::
706 {% macro input(name, value='', type='text') -%}
707 <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
710 {%- macro textarea(name, value='', rows=10, cols=40) -%}
711 <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
712 }}">{{ value|e }}</textarea>
715 The easiest and most flexible is importing the whole module into a variable.
716 That way you can access the attributes::
718 {% import 'forms.html' as forms %}
721 <dd>{{ forms.input('username') }}</dd>
723 <dd>{{ forms.input('password', type='password') }}</dd>
725 <p>{{ forms.textarea('comment') }}</p>
728 Alternatively you can import names from the template into the current
731 {% from 'forms.html' import input as input_field, textarea %}
734 <dd>{{ input_field('username') }}</dd>
736 <dd>{{ input_field('password', type='password') }}</dd>
738 <p>{{ textarea('comment') }}</p>
740 Macros and variables starting with one ore more underscores are private and
744 .. _import-visibility:
746 Import Context Behavior
747 -----------------------
749 Per default included templates are passed the current context and imported
750 templates not. The reason for this is that imports unlike includes are
751 cached as imports are often used just as a module that holds macros.
753 This however can be changed of course explicitly. By adding `with context`
754 or `without context` to the import/include directive the current context
755 can be passed to the template and caching is disabled automatically.
759 {% from 'forms.html' import input with context %}
760 {% include 'header.html' without context %}
768 Jinja allows basic expressions everywhere. These work very similar to regular
769 Python and even if you're not working with Python you should feel comfortable
775 The simplest form of expressions are literals. Literals are representations
776 for Python objects such as strings and numbers. The following literals exist:
779 Everything between two double or single quotes is a string. They are
780 useful whenever you need a string in the template (for example as
781 arguments to function calls, filters or just to extend or include a
785 Integers and floating point numbers are created by just writing the
786 number down. If a dot is present the number is a float, otherwise an
787 integer. Keep in mind that for Python ``42`` and ``42.0`` is something
790 ['list', 'of', 'objects']:
791 Everything between two brackets is a list. Lists are useful to store
792 sequential data in or to iterate over them. For example you can easily
793 create a list of links using lists and tuples with a for loop::
796 {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
797 ('downloads.html', 'Downloads')] %}
798 <li><a href="{{ href }}">{{ caption }}</a></li>
802 ('tuple', 'of', 'values'):
803 Tuples are like lists, just that you can't modify them. If the tuple
804 only has one item you have to end it with a comma. Tuples are usually
805 used to represent items of two or more elements. See the example above
808 {'dict': 'of', 'key': 'and', 'value': 'pairs'}:
809 A dict in Python is a structure that combines keys and values. Keys must
810 be unique and always have exactly one value. Dicts are rarely used in
811 templates, they are useful in some rare cases such as the :func:`xmlattr`
815 true is always true and false is always false.
819 The special constants `true`, `false` and `none` are indeed lowercase.
820 Because that caused confusion in the past, when writing `True` expands
821 to an undefined variable that is considered false, all three of them can
822 be written in title case too (`True`, `False`, and `None`). However for
823 consistency (all Jinja identifiers are lowercase) you should use the
829 Jinja allows you to calculate with values. This is rarely useful in templates
830 but exists for completeness sake. The following operators are supported:
833 Adds two objects with each other. Usually numbers but if both objects are
834 strings or lists you can concatenate them this way. This however is not
835 the preferred way to concatenate strings! For string concatenation have
836 a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``.
839 Substract two numbers from each other. ``{{ 3 - 2 }}`` is ``1``.
842 Divide two numbers. The return value will be a floating point number.
843 ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.
846 Divide two numbers and return the truncated integer result.
847 ``{{ 20 / 7 }}`` is ``2``.
850 Calculate the remainder of an integer division between the left and right
851 operand. ``{{ 11 % 7 }}`` is ``4``.
854 Multiply the left operand with the right one. ``{{ 2 * 2 }}`` would
855 return ``4``. This can also be used to repeat string multiple times.
856 ``{{ '=' * 80 }}`` would print a bar of 80 equal signs.
859 Raise the left operand to the power of the right operand. ``{{ 2**3 }}``
865 For `if` statements / `for` filtering or `if` expressions it can be useful to
866 combine group multiple expressions:
869 Return true if the left and the right operand is true.
872 Return true if the left or the right operand is true.
875 negate a statement (see below).
882 The ``is`` and ``in`` operators support negation using an infix notation
883 too: ``foo is not bar`` and ``foo not in bar`` instead of ``not foo is bar``
884 and ``not foo in bar``. All other expressions require a prefix notation:
885 ``not (foo and bar).``
891 The following operators are very useful but don't fit into any of the other
895 Perform sequence / mapping containment test. Returns true if the left
896 operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for
900 Performs a :ref:`test <tests>`.
903 Applies a :ref:`filter <filters>`.
906 Converts all operands into strings and concatenates them.
907 ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is
908 ``'John'``) ``Hello John!``.
911 Call a callable: ``{{ post.render() }}``. Inside of the parentheses you
912 can use arguments and keyword arguments like in python:
913 ``{{ post.render(user, full=true) }}``.
916 Get an attribute of an object. (See :ref:`variables`)
924 It is also possible to use inline `if` expressions. These are useful in some
925 situations. For example you can use this to extend from one template if a
926 variable is defined, otherwise from the default layout template::
928 {% extends layout_template if layout_template is defined else 'master.html' %}
930 The general syntax is ``<do something> if <something is true> else <do
936 List of Builtin Filters
937 -----------------------
944 List of Builtin Tests
945 ---------------------
950 List of Global Functions
951 ------------------------
953 The following functions are available in the global scope by default:
955 .. function:: range([start,] stop[, step])
957 Return a list containing an arithmetic progression of integers.
958 range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
959 When step is given, it specifies the increment (or decrement).
960 For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
961 These are exactly the valid indices for a list of 4 elements.
963 This is useful to repeat a template block multiple times for example
964 to fill a list. Imagine you have 7 users in the list but you want to
965 render three empty items to enforce a height with CSS::
968 {% for user in users %}
969 <li>{{ user.username }}</li>
971 {% for number in range(10 - users|count) %}
972 <li class="empty"><span>...</span></li>
976 .. function:: lipsum(n=5, html=True, min=20, max=100)
978 Generates some lorem ipsum for the template. Per default five paragraphs
979 with HTML are generated each paragraph between 20 and 100 words. If html
980 is disabled regular text is returned. This is useful to generate simple
981 contents for layout testing.
983 .. function:: dict(\**items)
985 A convenient alternative to dict literals. ``{'foo': 'bar'}`` is the same
986 as ``dict(foo='bar')``.
992 The following sections cover the built-in Jinja2 extensions that may be
993 enabled by the application. The application could also provide further
994 extensions not covered by this documentation. In that case there should
995 be a separate document explaining the extensions.
997 .. _i18n-in-templates:
1002 If the i18n extension is enabled it's possible to mark parts in the template
1003 as translatable. To mark a section as translatable you can use `trans`::
1005 <p>{% trans %}Hello {{ user }}!{% endtrans %}</p>
1007 To translate a template expression --- say, using template filters or just
1008 accessing an attribute of an object --- you need to bind the expression to a
1009 name for use within the translation block::
1011 <p>{% trans user=user.username %}Hello {{ user }}!{% endtrans %}</p>
1013 If you need to bind more than one expression inside a `trans` tag, separate
1014 the pieces with a comma (``,``)::
1016 {% trans book_title=book.title, author=author.name %}
1017 This is {{ book_title }} by {{ author }}
1020 Inside trans tags no statements are allowed, only variable tags are.
1022 To pluralize, specify both the singular and plural forms with the `pluralize`
1023 tag, which appears between `trans` and `endtrans`::
1025 {% trans count=list|length %}
1026 There is {{ count }} {{ name }} object.
1028 There are {{ count }} {{ name }} objects.
1031 Per default the first variable in a block is used to determine the correct
1032 singular or plural form. If that doesn't work out you can specify the name
1033 which should be used for pluralizing by adding it as parameter to `pluralize`::
1035 {% trans ..., user_count=users|length %}...
1036 {% pluralize user_count %}...{% endtrans %}
1038 It's also possible to translate strings in expressions. For that purpose
1039 three functions exist:
1041 _ `gettext`: translate a single string
1042 - `ngettext`: translate a pluralizable string
1043 - `_`: alias for `gettext`
1045 For example you can print a translated string easily this way::
1047 {{ _('Hello World!') }}
1049 To use placeholders you can use the `format` filter::
1051 {{ _('Hello %(user)s!')|format(user=user.username) }}
1053 {{ _('Hello %s')|format(user.username) }}
1055 For multiple placeholders always use keyword arguments to `format` as other
1056 languages may not use the words in the same order.
1059 Expression Statement
1060 ~~~~~~~~~~~~~~~~~~~~
1062 If the expression-statement extension is loaded a tag called `do` is available
1063 that works exactly like the regular variable expression (``{{ ... }}``) just
1064 that it doesn't print anything. This can be used to modify lists::
1066 {% do navigation.append('a string') %}
1072 If the application enables the :ref:`loopcontrols-extension` it's possible to
1073 use `break` and `continue` in loops. When `break` is reached, the loop is
1074 terminated, if `continue` is eached the processing is stopped and continues
1075 with the next iteration.
1077 Here a loop that skips every second item::
1079 {% for user in users %}
1080 {%- if loop.index is even %}{% continue %}{% endif %}
1084 Likewise a look that stops processing after the 10th iteration::
1086 {% for user in users %}
1087 {%- if loop.index >= 10 %}{% break %}{% endif %}