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 delimiters. ``{% ... %}`` 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 be 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 .. versionchanged:: 2.4
417 If a template object was passed to the template context you can
418 extend from that object as well. Assuming the calling code passes
419 a layout template as `layout_template` to the environment, this
422 {% extends layout_template %}
424 Previously the `layout_template` variable had to be a string with
425 the layout template's filename for this to work.
431 When generating HTML from templates, there's always a risk that a variable will
432 include characters that affect the resulting HTML. There are two approaches:
433 manually escaping each variable or automatically escaping everything by default.
435 Jinja supports both, but what is used depends on the application configuration.
436 The default configuaration is no automatic escaping for various reasons:
438 - escaping everything except of safe values will also mean that Jinja is
439 escaping variables known to not include HTML such as numbers which is
440 a huge performance hit.
442 - The information about the safety of a variable is very fragile. It could
443 happen that by coercing safe and unsafe values the return value is double
446 Working with Manual Escaping
447 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
449 If manual escaping is enabled it's **your** responsibility to escape
450 variables if needed. What to escape? If you have a variable that *may*
451 include any of the following chars (``>``, ``<``, ``&``, or ``"``) you
452 **have to** escape it unless the variable contains well-formed and trusted
453 HTML. Escaping works by piping the variable through the ``|e`` filter:
454 ``{{ user.username|e }}``.
456 Working with Automatic Escaping
457 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
459 When automatic escaping is enabled everything is escaped by default except
460 for values explicitly marked as safe. Those can either be marked by the
461 application or in the template by using the `|safe` filter. The main
462 problem with this approach is that Python itself doesn't have the concept
463 of tainted values so the information if a value is safe or unsafe can get
464 lost. If the information is lost escaping will take place which means that
465 you could end up with double escaped contents.
467 Double escaping is easy to avoid however, just rely on the tools Jinja2
468 provides and don't use builtin Python constructs such as the string modulo
471 Functions returning template data (macros, `super`, `self.BLOCKNAME`) return
474 String literals in templates with automatic escaping are considered unsafe
475 too. The reason for this is that the safe string is an extension to Python
476 and not every library will work properly with it.
479 List of Control Structures
480 --------------------------
482 A control structure refers to all those things that control the flow of a
483 program - conditionals (i.e. if/elif/else), for-loops, as well as things like
484 macros and blocks. Control structures appear inside ``{% ... %}`` blocks
485 in the default syntax.
490 Loop over each item in a sequence. For example, to display a list of users
491 provided in a variable called `users`::
495 {% for user in users %}
496 <li>{{ user.username|e }}</li>
500 Inside of a for loop block you can access some special variables:
502 +-----------------------+---------------------------------------------------+
503 | Variable | Description |
504 +=======================+===================================================+
505 | `loop.index` | The current iteration of the loop. (1 indexed) |
506 +-----------------------+---------------------------------------------------+
507 | `loop.index0` | The current iteration of the loop. (0 indexed) |
508 +-----------------------+---------------------------------------------------+
509 | `loop.revindex` | The number of iterations from the end of the loop |
511 +-----------------------+---------------------------------------------------+
512 | `loop.revindex0` | The number of iterations from the end of the loop |
514 +-----------------------+---------------------------------------------------+
515 | `loop.first` | True if first iteration. |
516 +-----------------------+---------------------------------------------------+
517 | `loop.last` | True if last iteration. |
518 +-----------------------+---------------------------------------------------+
519 | `loop.length` | The number of items in the sequence. |
520 +-----------------------+---------------------------------------------------+
521 | `loop.cycle` | A helper function to cycle between a list of |
522 | | sequences. See the explanation below. |
523 +-----------------------+---------------------------------------------------+
525 Within a for-loop, it's possible to cycle among a list of strings/variables
526 each time through the loop by using the special `loop.cycle` helper::
528 {% for row in rows %}
529 <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
532 With Jinja 2.1 an extra `cycle` helper exists that allows loop-unbound
533 cycling. For more information have a look at the :ref:`builtin-globals`.
537 Unlike in Python it's not possible to `break` or `continue` in a loop. You
538 can however filter the sequence during iteration which allows you to skip
539 items. The following example skips all the users which are hidden::
541 {% for user in users if not user.hidden %}
542 <li>{{ user.username|e }}</li>
545 The advantage is that the special `loop` variable will count correctly thus
546 not counting the users not iterated over.
548 If no iteration took place because the sequence was empty or the filtering
549 removed all the items from the sequence you can render a replacement block
553 {% for user in users %}
554 <li>{{ user.username|e }}</li>
556 <li><em>no users found</em></li>
560 It is also possible to use loops recursively. This is useful if you are
561 dealing with recursive data such as sitemaps. To use loops recursively you
562 basically have to add the `recursive` modifier to the loop definition and
563 call the `loop` variable with the new iterable where you want to recurse.
565 The following example implements a sitemap with recursive loops::
568 {%- for item in sitemap recursive %}
569 <li><a href="{{ item.href|e }}">{{ item.title }}</a>
570 {%- if item.children -%}
571 <ul class="submenu">{{ loop(item.children) }}</ul>
580 The `if` statement in Jinja is comparable with the if statements of Python.
581 In the simplest form you can use it to test if a variable is defined, not
586 {% for user in users %}
587 <li>{{ user.username|e }}</li>
592 For multiple branches `elif` and `else` can be used like in Python. You can
593 use more complex :ref:`expressions` there too::
597 {% elif kenny.dead %}
598 You killed Kenny! You bastard!!!
600 Kenny looks okay --- so far
603 If can also be used as :ref:`inline expression <if-expression>` and for
604 :ref:`loop filtering <loop-filtering>`.
610 Macros are comparable with functions in regular programming languages. They
611 are useful to put often used idioms into reusable functions to not repeat
614 Here a small example of a macro that renders a form element::
616 {% macro input(name, value='', type='text', size=20) -%}
617 <input type="{{ type }}" name="{{ name }}" value="{{
618 value|e }}" size="{{ size }}">
621 The macro can then be called like a function in the namespace::
623 <p>{{ input('username') }}</p>
624 <p>{{ input('password', type='password') }}</p>
626 If the macro was defined in a different template you have to
627 :ref:`import <import>` it first.
629 Inside macros you have access to three special variables:
632 If more positional arguments are passed to the macro than accepted by the
633 macro they end up in the special `varargs` variable as list of values.
636 Like `varargs` but for keyword arguments. All unconsumed keyword
637 arguments are stored in this special variable.
640 If the macro was called from a :ref:`call<call>` tag the caller is stored
641 in this variable as macro which can be called.
643 Macros also expose some of their internal details. The following attributes
644 are available on a macro object:
647 The name of the macro. ``{{ input.name }}`` will print ``input``.
650 A tuple of the names of arguments the macro accepts.
653 A tuple of default values.
656 This is `true` if the macro accepts extra keyword arguments (ie: accesses
657 the special `kwargs` variable).
660 This is `true` if the macro accepts extra positional arguments (ie:
661 accesses the special `varargs` variable).
664 This is `true` if the macro accesses the special `caller` variable and may
665 be called from a :ref:`call<call>` tag.
667 If a macro name starts with an underscore it's not exported and can't
676 In some cases it can be useful to pass a macro to another macro. For this
677 purpose you can use the special `call` block. The following example shows
678 a macro that takes advantage of the call functionality and how it can be
681 {% macro render_dialog(title, class='dialog') -%}
682 <div class="{{ class }}">
684 <div class="contents">
690 {% call render_dialog('Hello World') %}
691 This is a simple dialog rendered by using a macro and
695 It's also possible to pass arguments back to the call block. This makes it
696 useful as replacement for loops. Generally speaking a call block works
697 exactly like an macro, just that it doesn't have a name.
699 Here an example of how a call block can be used with arguments::
701 {% macro dump_users(users) -%}
703 {%- for user in users %}
704 <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
709 {% call(user) dump_users(list_of_user) %}
712 <dd>{{ user.realname|e }}</dd>
714 <dd>{{ user.description }}</dd>
722 Filter sections allow you to apply regular Jinja2 filters on a block of
723 template data. Just wrap the code in the special `filter` section::
726 This text becomes uppercase
733 Inside code blocks you can also assign values to variables. Assignments at
734 top level (outside of blocks, macros or loops) are exported from the template
735 like top level macros and can be imported by other templates.
737 Assignments use the `set` tag and can have multiple targets::
739 {% set navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
740 {% set key, value = call_something() %}
746 The `extends` tag can be used to extend a template from another one. You
747 can have multiple of them in a file but only one of them may be executed
748 at the time. See the section about :ref:`template-inheritance` above.
754 Blocks are used for inheritance and act as placeholders and replacements
755 at the same time. They are documented in detail as part of the section
756 about :ref:`template-inheritance`.
762 The `include` statement is useful to include a template and return the
763 rendered contents of that file into the current namespace::
765 {% include 'header.html' %}
767 {% include 'footer.html' %}
769 Included templates have access to the variables of the active context by
770 default. For more details about context behavior of imports and includes
771 see :ref:`import-visibility`.
773 From Jinja 2.2 onwards you can mark an include with ``ignore missing`` in
774 which case Jinja will ignore the statement if the template to be ignored
775 does not exist. When combined with ``with`` or ``without context`` it has
776 to be placed *before* the context visibility statement. Here some valid
779 {% include "sidebar.html" ignore missing %}
780 {% include "sidebar.html" ignore missing with context %}
781 {% include "sidebar.html" ignore missing without context %}
783 .. versionadded:: 2.2
785 You can also provide a list of templates that are checked for existence
786 before inclusion. The first template that exists will be included. If
787 `ignore missing` is given, it will fall back to rendering nothing if
788 none of the templates exist, otherwise it will raise an exception.
792 {% include ['page_detailed.html', 'page.html'] %}
793 {% include ['special_sidebar.html', 'sidebar.html'] ignore missing %}
795 .. versionchanged:: 2.4
796 If a template object was passed to the template context you can
797 include that object using `include`.
804 Jinja2 supports putting often used code into macros. These macros can go into
805 different templates and get imported from there. This works similar to the
806 import statements in Python. It's important to know that imports are cached
807 and imported templates don't have access to the current template variables,
808 just the globals by defualt. For more details about context behavior of
809 imports and includes see :ref:`import-visibility`.
811 There are two ways to import templates. You can import the complete template
812 into a variable or request specific macros / exported variables from it.
814 Imagine we have a helper module that renders forms (called `forms.html`)::
816 {% macro input(name, value='', type='text') -%}
817 <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
820 {%- macro textarea(name, value='', rows=10, cols=40) -%}
821 <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
822 }}">{{ value|e }}</textarea>
825 The easiest and most flexible is importing the whole module into a variable.
826 That way you can access the attributes::
828 {% import 'forms.html' as forms %}
831 <dd>{{ forms.input('username') }}</dd>
833 <dd>{{ forms.input('password', type='password') }}</dd>
835 <p>{{ forms.textarea('comment') }}</p>
838 Alternatively you can import names from the template into the current
841 {% from 'forms.html' import input as input_field, textarea %}
844 <dd>{{ input_field('username') }}</dd>
846 <dd>{{ input_field('password', type='password') }}</dd>
848 <p>{{ textarea('comment') }}</p>
850 Macros and variables starting with one ore more underscores are private and
853 .. versionchanged:: 2.4
854 If a template object was passed to the template context you can
855 import from that object.
858 .. _import-visibility:
860 Import Context Behavior
861 -----------------------
863 Per default included templates are passed the current context and imported
864 templates not. The reason for this is that imports unlike includes are
865 cached as imports are often used just as a module that holds macros.
867 This however can be changed of course explicitly. By adding `with context`
868 or `without context` to the import/include directive the current context
869 can be passed to the template and caching is disabled automatically.
873 {% from 'forms.html' import input with context %}
874 {% include 'header.html' without context %}
878 In Jinja 2.0 the context that was passed to the included template
879 did not include variables defined in the template. As a matter of
880 fact this did not work::
882 {% for box in boxes %}
883 {% include "render_box.html" %}
886 The included template ``render_box.html`` is *not* able to access
887 `box` in Jinja 2.0. As of Jinja 2.1 ``render_box.html`` *is* able
896 Jinja allows basic expressions everywhere. These work very similar to regular
897 Python and even if you're not working with Python you should feel comfortable
903 The simplest form of expressions are literals. Literals are representations
904 for Python objects such as strings and numbers. The following literals exist:
907 Everything between two double or single quotes is a string. They are
908 useful whenever you need a string in the template (for example as
909 arguments to function calls, filters or just to extend or include a
913 Integers and floating point numbers are created by just writing the
914 number down. If a dot is present the number is a float, otherwise an
915 integer. Keep in mind that for Python ``42`` and ``42.0`` is something
918 ['list', 'of', 'objects']:
919 Everything between two brackets is a list. Lists are useful to store
920 sequential data in or to iterate over them. For example you can easily
921 create a list of links using lists and tuples with a for loop::
924 {% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
925 ('downloads.html', 'Downloads')] %}
926 <li><a href="{{ href }}">{{ caption }}</a></li>
930 ('tuple', 'of', 'values'):
931 Tuples are like lists, just that you can't modify them. If the tuple
932 only has one item you have to end it with a comma. Tuples are usually
933 used to represent items of two or more elements. See the example above
936 {'dict': 'of', 'key': 'and', 'value': 'pairs'}:
937 A dict in Python is a structure that combines keys and values. Keys must
938 be unique and always have exactly one value. Dicts are rarely used in
939 templates, they are useful in some rare cases such as the :func:`xmlattr`
943 true is always true and false is always false.
947 The special constants `true`, `false` and `none` are indeed lowercase.
948 Because that caused confusion in the past, when writing `True` expands
949 to an undefined variable that is considered false, all three of them can
950 be written in title case too (`True`, `False`, and `None`). However for
951 consistency (all Jinja identifiers are lowercase) you should use the
957 Jinja allows you to calculate with values. This is rarely useful in templates
958 but exists for completeness' sake. The following operators are supported:
961 Adds two objects together. Usually the objects are numbers but if both are
962 strings or lists you can concatenate them this way. This however is not
963 the preferred way to concatenate strings! For string concatenation have
964 a look at the ``~`` operator. ``{{ 1 + 1 }}`` is ``2``.
967 Substract the second number from the first one. ``{{ 3 - 2 }}`` is ``1``.
970 Divide two numbers. The return value will be a floating point number.
971 ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.
974 Divide two numbers and return the truncated integer result.
975 ``{{ 20 // 7 }}`` is ``2``.
978 Calculate the remainder of an integer division. ``{{ 11 % 7 }}`` is ``4``.
981 Multiply the left operand with the right one. ``{{ 2 * 2 }}`` would
982 return ``4``. This can also be used to repeat a string multiple times.
983 ``{{ '=' * 80 }}`` would print a bar of 80 equal signs.
986 Raise the left operand to the power of the right operand. ``{{ 2**3 }}``
993 Compares two objects for equality.
996 Compares two objects for inequality.
999 `true` if the left hand side is greater than the right hand side.
1002 `true` if the left hand side is greater or equal to the right hand side.
1005 `true` if the left hand side is lower than the right hand side.
1008 `true` if the left hand side is lower or equal to the right hand side.
1013 For `if` statements, `for` filtering or `if` expressions it can be useful to
1014 combine multiple expressions:
1017 Return true if the left and the right operand is true.
1020 Return true if the left or the right operand is true.
1023 negate a statement (see below).
1026 group an expression.
1028 .. admonition:: Note
1030 The ``is`` and ``in`` operators support negation using an infix notation
1031 too: ``foo is not bar`` and ``foo not in bar`` instead of ``not foo is bar``
1032 and ``not foo in bar``. All other expressions require a prefix notation:
1033 ``not (foo and bar).``
1039 The following operators are very useful but don't fit into any of the other
1043 Perform sequence / mapping containment test. Returns true if the left
1044 operand is contained in the right. ``{{ 1 in [1, 2, 3] }}`` would for
1045 example return true.
1048 Performs a :ref:`test <tests>`.
1051 Applies a :ref:`filter <filters>`.
1054 Converts all operands into strings and concatenates them.
1055 ``{{ "Hello " ~ name ~ "!" }}`` would return (assuming `name` is
1056 ``'John'``) ``Hello John!``.
1059 Call a callable: ``{{ post.render() }}``. Inside of the parentheses you
1060 can use positional arguments and keyword arguments like in python:
1061 ``{{ post.render(user, full=true) }}``.
1064 Get an attribute of an object. (See :ref:`variables`)
1072 It is also possible to use inline `if` expressions. These are useful in some
1073 situations. For example you can use this to extend from one template if a
1074 variable is defined, otherwise from the default layout template::
1076 {% extends layout_template if layout_template is defined else 'master.html' %}
1078 The general syntax is ``<do something> if <something is true> else <do
1081 The `else` part is optional. If not provided the else block implicitly
1082 evaluates into an undefined object::
1084 {{ '[%s]' % page.title if page.title }}
1087 .. _builtin-filters:
1089 List of Builtin Filters
1090 -----------------------
1097 List of Builtin Tests
1098 ---------------------
1102 .. _builtin-globals:
1104 List of Global Functions
1105 ------------------------
1107 The following functions are available in the global scope by default:
1109 .. function:: range([start,] stop[, step])
1111 Return a list containing an arithmetic progression of integers.
1112 range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
1113 When step is given, it specifies the increment (or decrement).
1114 For example, range(4) returns [0, 1, 2, 3]. The end point is omitted!
1115 These are exactly the valid indices for a list of 4 elements.
1117 This is useful to repeat a template block multiple times for example
1118 to fill a list. Imagine you have 7 users in the list but you want to
1119 render three empty items to enforce a height with CSS::
1122 {% for user in users %}
1123 <li>{{ user.username }}</li>
1125 {% for number in range(10 - users|count) %}
1126 <li class="empty"><span>...</span></li>
1130 .. function:: lipsum(n=5, html=True, min=20, max=100)
1132 Generates some lorem ipsum for the template. Per default five paragraphs
1133 with HTML are generated each paragraph between 20 and 100 words. If html
1134 is disabled regular text is returned. This is useful to generate simple
1135 contents for layout testing.
1137 .. function:: dict(\**items)
1139 A convenient alternative to dict literals. ``{'foo': 'bar'}`` is the same
1140 as ``dict(foo='bar')``.
1142 .. class:: cycler(\*items)
1144 The cycler allows you to cycle among values similar to how `loop.cycle`
1145 works. Unlike `loop.cycle` however you can use this cycler outside of
1146 loops or over multiple loops.
1148 This is for example very useful if you want to show a list of folders and
1149 files, with the folders on top, but both in the same list with alternating
1152 The following example shows how `cycler` can be used::
1154 {% set row_class = cycler('odd', 'even') %}
1155 <ul class="browser">
1156 {% for folder in folders %}
1157 <li class="folder {{ row_class.next() }}">{{ folder|e }}</li>
1159 {% for filename in files %}
1160 <li class="file {{ row_class.next() }}">{{ filename|e }}</li>
1164 A cycler has the following attributes and methods:
1168 Resets the cycle to the first item.
1172 Goes one item a head and returns the then current item.
1174 .. attribute:: current
1176 Returns the current item.
1178 **new in Jinja 2.1**
1180 .. class:: joiner(sep=', ')
1182 A tiny helper that can be use to "join" multiple sections. A joiner is
1183 passed a string and will return that string every time it's called, except
1184 the first time in which situation it returns an empty string. You can
1185 use this to join things::
1187 {% set pipe = joiner("|") %}
1188 {% if categories %} {{ pipe() }}
1189 Categories: {{ categories|join(", ") }}
1191 {% if author %} {{ pipe() }}
1192 Author: {{ author() }}
1194 {% if can_edit %} {{ pipe() }}
1195 <a href="?action=edit">Edit</a>
1198 **new in Jinja 2.1**
1204 The following sections cover the built-in Jinja2 extensions that may be
1205 enabled by the application. The application could also provide further
1206 extensions not covered by this documentation. In that case there should
1207 be a separate document explaining the extensions.
1209 .. _i18n-in-templates:
1214 If the i18n extension is enabled it's possible to mark parts in the template
1215 as translatable. To mark a section as translatable you can use `trans`::
1217 <p>{% trans %}Hello {{ user }}!{% endtrans %}</p>
1219 To translate a template expression --- say, using template filters or just
1220 accessing an attribute of an object --- you need to bind the expression to a
1221 name for use within the translation block::
1223 <p>{% trans user=user.username %}Hello {{ user }}!{% endtrans %}</p>
1225 If you need to bind more than one expression inside a `trans` tag, separate
1226 the pieces with a comma (``,``)::
1228 {% trans book_title=book.title, author=author.name %}
1229 This is {{ book_title }} by {{ author }}
1232 Inside trans tags no statements are allowed, only variable tags are.
1234 To pluralize, specify both the singular and plural forms with the `pluralize`
1235 tag, which appears between `trans` and `endtrans`::
1237 {% trans count=list|length %}
1238 There is {{ count }} {{ name }} object.
1240 There are {{ count }} {{ name }} objects.
1243 Per default the first variable in a block is used to determine the correct
1244 singular or plural form. If that doesn't work out you can specify the name
1245 which should be used for pluralizing by adding it as parameter to `pluralize`::
1247 {% trans ..., user_count=users|length %}...
1248 {% pluralize user_count %}...{% endtrans %}
1250 It's also possible to translate strings in expressions. For that purpose
1251 three functions exist:
1253 _ `gettext`: translate a single string
1254 - `ngettext`: translate a pluralizable string
1255 - `_`: alias for `gettext`
1257 For example you can print a translated string easily this way::
1259 {{ _('Hello World!') }}
1261 To use placeholders you can use the `format` filter::
1263 {{ _('Hello %(user)s!')|format(user=user.username) }}
1265 For multiple placeholders always use keyword arguments to `format` as other
1266 languages may not use the words in the same order.
1268 .. versionchanged:: 2.5
1270 If newstyle gettext calls are activated (:ref:`newstyle-gettext`), using
1271 placeholders is a lot easier:
1273 .. sourcecode:: html+jinja
1275 {{ gettext('Hello World!') }}
1276 {{ gettext('Hello %(name)s!', name='World') }}
1277 {{ ngettext('%(num)d apple', '%(num)d apples', apples|count) }}
1279 Note that the `ngettext` function's format string automatically receives
1280 the count as `num` parameter additionally to the regular parameters.
1283 Expression Statement
1284 ~~~~~~~~~~~~~~~~~~~~
1286 If the expression-statement extension is loaded a tag called `do` is available
1287 that works exactly like the regular variable expression (``{{ ... }}``) just
1288 that it doesn't print anything. This can be used to modify lists::
1290 {% do navigation.append('a string') %}
1296 If the application enables the :ref:`loopcontrols-extension` it's possible to
1297 use `break` and `continue` in loops. When `break` is reached, the loop is
1298 terminated; if `continue` is reached, the processing is stopped and continues
1299 with the next iteration.
1301 Here a loop that skips every second item::
1303 {% for user in users %}
1304 {%- if loop.index is even %}{% continue %}{% endif %}
1308 Likewise a look that stops processing after the 10th iteration::
1310 {% for user in users %}
1311 {%- if loop.index >= 10 %}{% break %}{% endif %}
1318 .. versionadded:: 2.3
1320 If the application enables the :ref:`with-extension` it is possible to
1321 use the `with` keyword in templates. This makes it possible to create
1322 a new inner scope. Variables set within this scope are not visible
1323 outside of the scope.
1325 With in a nutshell::
1329 {{ foo }} foo is 42 here
1331 foo is not visible here any longer
1333 Because it is common to set variables at the beginning of the scope
1334 you can do that within the with statement. The following two examples
1346 .. _autoescape-overrides:
1348 Autoescape Extension
1349 --------------------
1351 .. versionadded:: 2.4
1353 If the application enables the :ref:`autoescape-extension` one can
1354 activate and deactivate the autoescaping from within the templates.
1358 {% autoescape true %}
1359 Autoescaping is active within this block
1362 {% autoescape false %}
1363 Autoescaping is inactive within this block
1366 After the `endautoescape` the behavior is reverted to what it was before.