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 commas: ``{{ 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 use 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>
255 Since Jinja 2.2 line-based comments are available as well. For example if
256 the line-comment prefix is configured to be ``##`` everything from ``##`` to
257 the end of the line is ignored (excluding the newline sign)::
260 <li>{{ item }}</li> ## this comment is ignored
264 .. _template-inheritance:
269 The most powerful part of Jinja is template inheritance. Template inheritance
270 allows you to build a base "skeleton" template that contains all the common
271 elements of your site and defines **blocks** that child templates can override.
273 Sounds complicated but is very basic. It's easiest to understand it by starting
280 This template, which we'll call ``base.html``, defines a simple HTML skeleton
281 document that you might use for a simple two-column page. It's the job of
282 "child" templates to fill the empty blocks with content::
284 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
286 <html xmlns="http://www.w3.org/1999/xhtml">
289 <link rel="stylesheet" href="style.css" />
290 <title>{% block title %}{% endblock %} - My Webpage</title>
294 <div id="content">{% block content %}{% endblock %}</div>
297 © Copyright 2008 by <a href="http://domain.invalid/">you</a>.
302 In this example, the ``{% block %}`` tags define four blocks that child templates
303 can fill in. All the `block` tag does is to tell the template engine that a
304 child template may override those portions of the template.
309 A child template might look like this::
311 {% extends "base.html" %}
312 {% block title %}Index{% endblock %}
315 <style type="text/css">
316 .important { color: #336699; }
321 <p class="important">
322 Welcome on my awesome homepage.
326 The ``{% extends %}`` tag is the key here. It tells the template engine that
327 this template "extends" another template. When the template system evaluates
328 this template, first it locates the parent. The extends tag should be the
329 first tag in the template. Everything before it is printed out normally and
330 may cause confusion. For details about this behavior and how to take
331 advantage of it, see :ref:`null-master-fallback`.
333 The filename of the template depends on the template loader. For example the
334 :class:`FileSystemLoader` allows you to access other templates by giving the
335 filename. You can access templates in subdirectories with an slash::
337 {% extends "layout/default.html" %}
339 But this behavior can depend on the application embedding Jinja. Note that
340 since the child template doesn't define the ``footer`` block, the value from
341 the parent template is used instead.
343 You can't define multiple ``{% block %}`` tags with the same name in the
344 same template. This limitation exists because a block tag works in "both"
345 directions. That is, a block tag doesn't just provide a hole to fill - it
346 also defines the content that fills the hole in the *parent*. If there
347 were two similarly-named ``{% block %}`` tags in a template, that template's
348 parent wouldn't know which one of the blocks' content to use.
350 If you want to print a block multiple times you can however use the special
351 `self` variable and call the block with that name::
353 <title>{% block title %}{% endblock %}</title>
354 <h1>{{ self.title() }}</h1>
355 {% block body %}{% endblock %}
361 It's possible to render the contents of the parent block by calling `super`.
362 This gives back the results of the parent block::
365 <h3>Table Of Contents</h3>
374 Jinja2 allows you to put the name of the block after the end tag for better
378 {% block inner_sidebar %}
380 {% endblock inner_sidebar %}
381 {% endblock sidebar %}
383 However the name after the `endblock` word must match the block name.
386 Block Nesting and Scope
387 ~~~~~~~~~~~~~~~~~~~~~~~
389 Blocks can be nested for more complex layouts. However per default blocks
390 may not access variables from outer scopes::
392 {% for item in seq %}
393 <li>{% block loop_item %}{{ item }}{% endblock %}</li>
396 This example would output empty ``<li>`` items because `item` is unavailable
397 inside the block. The reason for this is that if the block is replaced by
398 a child template a variable would appear that was not defined in the block or
399 passed to the context.
401 Starting with Jinja 2.2 you can explicitly specify that variables are
402 available in a block by setting the block to "scoped" by adding the `scoped`
403 modifier to a block declaration::
405 {% for item in seq %}
406 <li>{% block loop_item scoped %}{{ item }}{% endblock %}</li>
409 When overriding a block the `scoped` modifier does not have to be provided.
415 When generating HTML from templates, there's always a risk that a variable will
416 include characters that affect the resulting HTML. There are two approaches:
417 manually escaping each variable or automatically escaping everything by default.
419 Jinja supports both, but what is used depends on the application configuration.
420 The default configuaration is no automatic escaping for various reasons:
422 - escaping everything except of safe values will also mean that Jinja is
423 escaping variables known to not include HTML such as numbers which is
424 a huge performance hit.
426 - The information about the safety of a variable is very fragile. It could
427 happen that by coercing safe and unsafe values the return value is double
430 Working with Manual Escaping
431 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
433 If manual escaping is enabled it's **your** responsibility to escape
434 variables if needed. What to escape? If you have a variable that *may*
435 include any of the following chars (``>``, ``<``, ``&``, or ``"``) you
436 **have to** escape it unless the variable contains well-formed and trusted
437 HTML. Escaping works by piping the variable through the ``|e`` filter:
438 ``{{ user.username|e }}``.
440 Working with Automatic Escaping
441 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
443 When automatic escaping is enabled everything is escaped by default except
444 for values explicitly marked as safe. Those can either be marked by the
445 application or in the template by using the `|safe` filter. The main
446 problem with this approach is that Python itself doesn't have the concept
447 of tainted values so the information if a value is safe or unsafe can get
448 lost. If the information is lost escaping will take place which means that
449 you could end up with double escaped contents.
451 Double escaping is easy to avoid however, just rely on the tools Jinja2
452 provides and don't use builtin Python constructs such as the string modulo
455 Functions returning template data (macros, `super`, `self.BLOCKNAME`) return
458 String literals in templates with automatic escaping are considered unsafe
459 too. The reason for this is that the safe string is an extension to Python
460 and not every library will work properly with it.
463 List of Control Structures
464 --------------------------
466 A control structure refers to all those things that control the flow of a
467 program - conditionals (i.e. if/elif/else), for-loops, as well as things like
468 macros and blocks. Control structures appear inside ``{% ... %}`` blocks
469 in the default syntax.
474 Loop over each item in a sequence. For example, to display a list of users
475 provided in a variable called `users`::
479 {% for user in users %}
480 <li>{{ user.username|e }}</li>
484 Inside of a for loop block you can access some special variables:
486 +-----------------------+---------------------------------------------------+
487 | Variable | Description |
488 +=======================+===================================================+
489 | `loop.index` | The current iteration of the loop. (1 indexed) |
490 +-----------------------+---------------------------------------------------+
491 | `loop.index0` | The current iteration of the loop. (0 indexed) |
492 +-----------------------+---------------------------------------------------+
493 | `loop.revindex` | The number of iterations from the end of the loop |
495 +-----------------------+---------------------------------------------------+
496 | `loop.revindex0` | The number of iterations from the end of the loop |
498 +-----------------------+---------------------------------------------------+
499 | `loop.first` | True if first iteration. |
500 +-----------------------+---------------------------------------------------+
501 | `loop.last` | True if last iteration. |
502 +-----------------------+---------------------------------------------------+
503 | `loop.length` | The number of items in the sequence. |
504 +-----------------------+---------------------------------------------------+
505 | `loop.cycle` | A helper function to cycle between a list of |
506 | | sequences. See the explanation below. |
507 +-----------------------+---------------------------------------------------+
509 Within a for-loop, it's possible to cycle among a list of strings/variables
510 each time through the loop by using the special `loop.cycle` helper::
512 {% for row in rows %}
513 <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
516 With Jinja 2.1 an extra `cycle` helper exists that allows loop-unbound
517 cycling. For more information have a look at the :ref:`builtin-globals`.
521 Unlike in Python it's not possible to `break` or `continue` in a loop. You
522 can however filter the sequence during iteration which allows you to skip
523 items. The following example skips all the users which are hidden::
525 {% for user in users if not user.hidden %}
526 <li>{{ user.username|e }}</li>
529 The advantage is that the special `loop` variable will count correctly thus
530 not counting the users not iterated over.
532 If no iteration took place because the sequence was empty or the filtering
533 removed all the items from the sequence you can render a replacement block
537 {% for user in users %}
538 <li>{{ user.username|e }}</li>
540 <li><em>no users found</em></li>
544 It is also possible to use loops recursively. This is useful if you are
545 dealing with recursive data such as sitemaps. To use loops recursively you
546 basically have to add the `recursive` modifier to the loop definition and
547 call the `loop` variable with the new iterable where you want to recurse.
549 The following example implements a sitemap with recursive loops::
552 {%- for item in sitemap recursive %}
553 <li><a href="{{ item.href|e }}">{{ item.title }}</a>
554 {%- if item.children -%}
555 <ul class="submenu">{{ loop(item.children) }}</ul>
564 The `if` statement in Jinja is comparable with the if statements of Python.
565 In the simplest form you can use it to test if a variable is defined, not
570 {% for user in users %}
571 <li>{{ user.username|e }}</li>
576 For multiple branches `elif` and `else` can be used like in Python. You can
577 use more complex :ref:`expressions` there too::
581 {% elif kenny.dead %}
582 You killed Kenny! You bastard!!!
584 Kenny looks okay --- so far
587 If can also be used as :ref:`inline expression <if-expression>` and for
588 :ref:`loop filtering <loop-filtering>`.
594 Macros are comparable with functions in regular programming languages. They
595 are useful to put often used idioms into reusable functions to not repeat
598 Here a small example of a macro that renders a form element::
600 {% macro input(name, value='', type='text', size=20) -%}
601 <input type="{{ type }}" name="{{ name }}" value="{{
602 value|e }}" size="{{ size }}">
605 The macro can then be called like a function in the namespace::
607 <p>{{ input('username') }}</p>
608 <p>{{ input('password', type='password') }}</p>
610 If the macro was defined in a different template you have to
611 :ref:`import <import>` it first.
613 Inside macros you have access to three special variables:
616 If more positional arguments are passed to the macro than accepted by the
617 macro they end up in the special `varargs` variable as list of values.
620 Like `varargs` but for keyword arguments. All unconsumed keyword
621 arguments are stored in this special variable.
624 If the macro was called from a :ref:`call<call>` tag the caller is stored
625 in this variable as macro which can be called.
627 Macros also expose some of their internal details. The following attributes
628 are available on a macro object:
631 The name of the macro. ``{{ input.name }}`` will print ``input``.
634 A tuple of the names of arguments the macro accepts.
637 A tuple of default values.
640 This is `true` if the macro accepts extra keyword arguments (ie: accesses
641 the special `kwargs` variable).
644 This is `true` if the macro accepts extra positional arguments (ie:
645 accesses the special `varargs` variable).
648 This is `true` if the macro accesses the special `caller` variable and may
649 be called from a :ref:`call<call>` tag.
651 If a macro name starts with an underscore it's not exported and can't
660 In some cases it can be useful to pass a macro to another macro. For this
661 purpose you can use the special `call` block. The following example shows
662 a macro that takes advantage of the call functionality and how it can be
665 {% macro render_dialog(title, class='dialog') -%}
666 <div class="{{ class }}">
668 <div class="contents">
674 {% call render_dialog('Hello World') %}
675 This is a simple dialog rendered by using a macro and
679 It's also possible to pass arguments back to the call block. This makes it
680 useful as replacement for loops. Generally speaking a call block works
681 exactly like an macro, just that it doesn't have a name.
683 Here an example of how a call block can be used with arguments::
685 {% macro dump_users(users) -%}
687 {%- for user in users %}
688 <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
693 {% call(user) dump_users(list_of_user) %}
696 <dd>{{ user.realname|e }}</dd>
698 <dd>{{ user.description }}</dd>
706 Filter sections allow you to apply regular Jinja2 filters on a block of
707 template data. Just wrap the code in the special `filter` section::
710 This text becomes uppercase
717 Inside code blocks you can also assign values to variables. Assignments at
718 top level (outside of blocks, macros or loops) are exported from the template
719 like top level macros and can be imported by other templates.
721 Assignments use the `set` tag and can have multiple targets::
723 {% set navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
724 {% set key, value = call_something() %}
730 The `extends` tag can be used to extend a template from another one. You
731 can have multiple of them in a file but only one of them may be executed
732 at the time. See the section about :ref:`template-inheritance` above.
738 Blocks are used for inheritance and act as placeholders and replacements
739 at the same time. They are documented in detail as part of the section
740 about :ref:`template-inheritance`.
746 The `include` statement is useful to include a template and return the
747 rendered contents of that file into the current namespace::
749 {% include 'header.html' %}
751 {% include 'footer.html' %}
753 Included templates have access to the variables of the active context by
754 default. For more details about context behavior of imports and includes
755 see :ref:`import-visibility`.
757 From Jinja 2.2 onwards you can mark an include with ``ignore missing`` in
758 which case Jinja will ignore the statement if the template to be ignored
759 does not exist. When combined with ``with`` or ``without context`` it has
760 to be placed *before* the context visibility statement. Here some valid
763 {% include "sidebar.html" ignore missing %}
764 {% include "sidebar.html" ignore missing with context %}
765 {% include "sidebar.html" ignore missing without context %}
767 .. versionadded:: 2.2
769 You can also provide a list of templates that are checked for existence
770 before inclusion. The first template that exists will be included. If
771 `ignore missing` is given, it will fall back to rendering nothing if
772 none of the templates exist, otherwise it will raise an exception.
776 {% include ['page_detailed.html', 'page.html'] %}
777 {% include ['special_sidebar.html', 'sidebar.html'] ignore missing %}
784 Jinja2 supports putting often used code into macros. These macros can go into
785 different templates and get imported from there. This works similar to the
786 import statements in Python. It's important to know that imports are cached
787 and imported templates don't have access to the current template variables,
788 just the globals by defualt. For more details about context behavior of
789 imports and includes see :ref:`import-visibility`.
791 There are two ways to import templates. You can import the complete template
792 into a variable or request specific macros / exported variables from it.
794 Imagine we have a helper module that renders forms (called `forms.html`)::
796 {% macro input(name, value='', type='text') -%}
797 <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
800 {%- macro textarea(name, value='', rows=10, cols=40) -%}
801 <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
802 }}">{{ value|e }}</textarea>
805 The easiest and most flexible is importing the whole module into a variable.
806 That way you can access the attributes::
808 {% import 'forms.html' as forms %}
811 <dd>{{ forms.input('username') }}</dd>
813 <dd>{{ forms.input('password', type='password') }}</dd>
815 <p>{{ forms.textarea('comment') }}</p>
818 Alternatively you can import names from the template into the current
821 {% from 'forms.html' import input as input_field, textarea %}
824 <dd>{{ input_field('username') }}</dd>
826 <dd>{{ input_field('password', type='password') }}</dd>
828 <p>{{ textarea('comment') }}</p>
830 Macros and variables starting with one ore more underscores are private and
834 .. _import-visibility:
836 Import Context Behavior
837 -----------------------
839 Per default included templates are passed the current context and imported
840 templates not. The reason for this is that imports unlike includes are
841 cached as imports are often used just as a module that holds macros.
843 This however can be changed of course explicitly. By adding `with context`
844 or `without context` to the import/include directive the current context
845 can be passed to the template and caching is disabled automatically.
849 {% from 'forms.html' import input with context %}
850 {% include 'header.html' without context %}
854 In Jinja 2.0 the context that was passed to the included template
855 did not include variables defined in the template. As a matter of
856 fact this did not work::
858 {% for box in boxes %}
859 {% include "render_box.html" %}
862 The included template ``render_box.html`` is not able to access
863 `box` in Jinja 2.0, but in Jinja 2.1.
871 Jinja allows basic expressions everywhere. These work very similar to regular
872 Python and even if you're not working with Python you should feel comfortable
878 The simplest form of expressions are literals. Literals are representations
879 for Python objects such as strings and numbers. The following literals exist:
882 Everything between two double or single quotes is a string. They are
883 useful whenever you need a string in the template (for example as
884 arguments to function calls, filters or just to extend or include a
888 Integers and floating point numbers are created by just writing the
889 number down. If a dot is present the number is a float, otherwise an
890 integer. Keep in mind that for Python ``42`` and ``42.0`` is something
893 ['list', 'of', 'objects']:
894 Everything between two brackets is a list. Lists are useful to store
895 sequential data in or to iterate over them. For example you can easily
896 create a list of links using lists and tuples with a for loop::
899 {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
900 ('downloads.html', 'Downloads')] %}
901 <li><a href="{{ href }}">{{ caption }}</a></li>
905 ('tuple', 'of', 'values'):
906 Tuples are like lists, just that you can't modify them. If the tuple
907 only has one item you have to end it with a comma. Tuples are usually
908 used to represent items of two or more elements. See the example above
911 {'dict': 'of', 'key': 'and', 'value': 'pairs'}:
912 A dict in Python is a structure that combines keys and values. Keys must
913 be unique and always have exactly one value. Dicts are rarely used in
914 templates, they are useful in some rare cases such as the :func:`xmlattr`
918 true is always true and false is always false.
922 The special constants `true`, `false` and `none` are indeed lowercase.
923 Because that caused confusion in the past, when writing `True` expands
924 to an undefined variable that is considered false, all three of them can
925 be written in title case too (`True`, `False`, and `None`). However for
926 consistency (all Jinja identifiers are lowercase) you should use the
932 Jinja allows you to calculate with values. This is rarely useful in templates
933 but exists for completeness' sake. The following operators are supported:
936 Adds two objects together. Usually the objects are numbers but if both are
937 strings or lists you can concatenate them this way. This however is not
938 the preferred way to concatenate strings! For string concatenation have
939 a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``.
942 Substract the second number from the first one. ``{{ 3 - 2 }}`` is ``1``.
945 Divide two numbers. The return value will be a floating point number.
946 ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.
949 Divide two numbers and return the truncated integer result.
950 ``{{ 20 / 7 }}`` is ``2``.
953 Calculate the remainder of an integer division. ``{{ 11 % 7 }}`` is ``4``.
956 Multiply the left operand with the right one. ``{{ 2 * 2 }}`` would
957 return ``4``. This can also be used to repeat a string multiple times.
958 ``{{ '=' * 80 }}`` would print a bar of 80 equal signs.
961 Raise the left operand to the power of the right operand. ``{{ 2**3 }}``
967 For `if` statements, `for` filtering or `if` expressions it can be useful to
968 combine multiple expressions:
971 Return true if the left and the right operand is true.
974 Return true if the left or the right operand is true.
977 negate a statement (see below).
984 The ``is`` and ``in`` operators support negation using an infix notation
985 too: ``foo is not bar`` and ``foo not in bar`` instead of ``not foo is bar``
986 and ``not foo in bar``. All other expressions require a prefix notation:
987 ``not (foo and bar).``
993 The following operators are very useful but don't fit into any of the other
997 Perform sequence / mapping containment test. Returns true if the left
998 operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for
1002 Performs a :ref:`test <tests>`.
1005 Applies a :ref:`filter <filters>`.
1008 Converts all operands into strings and concatenates them.
1009 ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is
1010 ``'John'``) ``Hello John!``.
1013 Call a callable: ``{{ post.render() }}``. Inside of the parentheses you
1014 can use positional arguments and keyword arguments like in python:
1015 ``{{ post.render(user, full=true) }}``.
1018 Get an attribute of an object. (See :ref:`variables`)
1026 It is also possible to use inline `if` expressions. These are useful in some
1027 situations. For example you can use this to extend from one template if a
1028 variable is defined, otherwise from the default layout template::
1030 {% extends layout_template if layout_template is defined else 'master.html' %}
1032 The general syntax is ``<do something> if <something is true> else <do
1035 The `else` part is optional. If not provided the else block implicitly
1036 evaluates into an undefined object::
1038 {{ '[%s]' % page.title if page.title }}
1041 .. _builtin-filters:
1043 List of Builtin Filters
1044 -----------------------
1051 List of Builtin Tests
1052 ---------------------
1056 .. _builtin-globals:
1058 List of Global Functions
1059 ------------------------
1061 The following functions are available in the global scope by default:
1063 .. function:: range([start,] stop[, step])
1065 Return a list containing an arithmetic progression of integers.
1066 range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
1067 When step is given, it specifies the increment (or decrement).
1068 For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
1069 These are exactly the valid indices for a list of 4 elements.
1071 This is useful to repeat a template block multiple times for example
1072 to fill a list. Imagine you have 7 users in the list but you want to
1073 render three empty items to enforce a height with CSS::
1076 {% for user in users %}
1077 <li>{{ user.username }}</li>
1079 {% for number in range(10 - users|count) %}
1080 <li class="empty"><span>...</span></li>
1084 .. function:: lipsum(n=5, html=True, min=20, max=100)
1086 Generates some lorem ipsum for the template. Per default five paragraphs
1087 with HTML are generated each paragraph between 20 and 100 words. If html
1088 is disabled regular text is returned. This is useful to generate simple
1089 contents for layout testing.
1091 .. function:: dict(\**items)
1093 A convenient alternative to dict literals. ``{'foo': 'bar'}`` is the same
1094 as ``dict(foo='bar')``.
1096 .. class:: cycler(\*items)
1098 The cycler allows you to cycle among values similar to how `loop.cycle`
1099 works. Unlike `loop.cycle` however you can use this cycler outside of
1100 loops or over multiple loops.
1102 This is for example very useful if you want to show a list of folders and
1103 files, with the folders on top, but both in the same list with alternating
1106 The following example shows how `cycler` can be used::
1108 {% set row_class = cycler('odd', 'even') %}
1109 <ul class="browser">
1110 {% for folder in folders %}
1111 <li class="folder {{ row_class.next() }}">{{ folder|e }}</li>
1113 {% for filename in files %}
1114 <li class="file {{ row_class.next() }}">{{ filename|e }}</li>
1118 A cycler has the following attributes and methods:
1122 Resets the cycle to the first item.
1126 Goes one item a head and returns the then current item.
1128 .. attribute:: current
1130 Returns the current item.
1132 **new in Jinja 2.1**
1134 .. class:: joiner(sep=', ')
1136 A tiny helper that can be use to "join" multiple sections. A joiner is
1137 passed a string and will return that string every time it's calld, except
1138 the first time in which situation it returns an empty string. You can
1139 use this to join things::
1141 {% set pipe = joiner("|") %}
1142 {% if categories %} {{ pipe() }}
1143 Categories: {{ categories|join(", ") }}
1145 {% if author %} {{ pipe() }}
1146 Author: {{ author() }}
1148 {% if can_edit %} {{ pipe() }}
1149 <a href="?action=edit">Edit</a>
1152 **new in Jinja 2.1**
1158 The following sections cover the built-in Jinja2 extensions that may be
1159 enabled by the application. The application could also provide further
1160 extensions not covered by this documentation. In that case there should
1161 be a separate document explaining the extensions.
1163 .. _i18n-in-templates:
1168 If the i18n extension is enabled it's possible to mark parts in the template
1169 as translatable. To mark a section as translatable you can use `trans`::
1171 <p>{% trans %}Hello {{ user }}!{% endtrans %}</p>
1173 To translate a template expression --- say, using template filters or just
1174 accessing an attribute of an object --- you need to bind the expression to a
1175 name for use within the translation block::
1177 <p>{% trans user=user.username %}Hello {{ user }}!{% endtrans %}</p>
1179 If you need to bind more than one expression inside a `trans` tag, separate
1180 the pieces with a comma (``,``)::
1182 {% trans book_title=book.title, author=author.name %}
1183 This is {{ book_title }} by {{ author }}
1186 Inside trans tags no statements are allowed, only variable tags are.
1188 To pluralize, specify both the singular and plural forms with the `pluralize`
1189 tag, which appears between `trans` and `endtrans`::
1191 {% trans count=list|length %}
1192 There is {{ count }} {{ name }} object.
1194 There are {{ count }} {{ name }} objects.
1197 Per default the first variable in a block is used to determine the correct
1198 singular or plural form. If that doesn't work out you can specify the name
1199 which should be used for pluralizing by adding it as parameter to `pluralize`::
1201 {% trans ..., user_count=users|length %}...
1202 {% pluralize user_count %}...{% endtrans %}
1204 It's also possible to translate strings in expressions. For that purpose
1205 three functions exist:
1207 _ `gettext`: translate a single string
1208 - `ngettext`: translate a pluralizable string
1209 - `_`: alias for `gettext`
1211 For example you can print a translated string easily this way::
1213 {{ _('Hello World!') }}
1215 To use placeholders you can use the `format` filter::
1217 {{ _('Hello %(user)s!')|format(user=user.username) }}
1219 {{ _('Hello %s')|format(user.username) }}
1221 For multiple placeholders always use keyword arguments to `format` as other
1222 languages may not use the words in the same order.
1225 Expression Statement
1226 ~~~~~~~~~~~~~~~~~~~~
1228 If the expression-statement extension is loaded a tag called `do` is available
1229 that works exactly like the regular variable expression (``{{ ... }}``) just
1230 that it doesn't print anything. This can be used to modify lists::
1232 {% do navigation.append('a string') %}
1238 If the application enables the :ref:`loopcontrols-extension` it's possible to
1239 use `break` and `continue` in loops. When `break` is reached, the loop is
1240 terminated, if `continue` is eached the processing is stopped and continues
1241 with the next iteration.
1243 Here a loop that skips every second item::
1245 {% for user in users %}
1246 {%- if loop.index is even %}{% continue %}{% endif %}
1250 Likewise a look that stops processing after the 10th iteration::
1252 {% for user in users %}
1253 {%- if loop.index >= 10 %}{% break %}{% endif %}
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