Template Designer Documentation

This document describes the syntax and semantics of the template engine and will be most useful as reference to those creating Jinja templates. As the template engine is very flexible the configuration from the application might be slightly different from here in terms of delimiters and behavior of undefined values.

Synopsis

A template is simply a text file. It can generate any text-based format (HTML, XML, CSV, LaTeX, etc.). It doesn’t have a specific extension, .html or .xml are just fine.

A template contains variables or expressions, which get replaced with values when the template is evaluated, and tags, which control the logic of the template. The template syntax is heavily inspired by Django and Python.

Below is a minimal template that illustrates a few basics. We will cover the details later in that document:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
    <title>My Webpage</title>
</head>
<body>
    <ul id="navigation">
    {% for item in navigation %}
        <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
    {% endfor %}
    </ul>

    <h1>My Webpage</h1>
    {{ a_variable }}
</body>
</html>

This covers the default settings. The application developer might have changed the syntax from {% foo %} to <% foo %> or something similar.

There are two kinds of delimiters. {% ... %} and {{ ... }}. The first one is used to execute statements such as for-loops or assign values, the latter prints the result of the expression to the template.

Variables

The application passes variables to the templates you can mess around in the template. Variables may have attributes or elements on them you can access too. How a variable looks like, heavily depends on the application providing those.

You can use a dot (.) to access attributes of a variable, alternative the so-called “subscript” syntax ([]) can be used. The following lines do the same:

{{ foo.bar }}
{{ foo['bar'] }}

It’s important to know that the curly braces are not part of the variable but the print statement. If you access variables inside tags don’t put the braces around.

If a variable or attribute does not exist you will get back an undefined value. What you can do with that kind of value depends on the application configuration, the default behavior is that it evaluates to an empty string if printed and that you can iterate over it, but every other operation fails.

Implementation

For convenience sake foo.bar in Jinja2 does the following things on the Python layer:

  • check if there is an attribute called bar on foo.
  • if there is not, check if there is an item 'bar' in foo.
  • if there is not, return an undefined object.

foo['bar'] on the other hand works mostly the same with the a small difference in the order:

  • check if there is an item 'bar' in foo.
  • if there is not, check if there is an attribute called bar on foo.
  • if there is not, return an undefined object.

This is important if an object has an item or attribute with the same name. Additionally there is the attr() filter that just looks up attributes.

Filters

Variables can be modified by filters. Filters are separated from the variable by a pipe symbol (|) and may have optional arguments in parentheses. Multiple filters can be chained. The output of one filter is applied to the next.

{{ name|striptags|title }} for example will remove all HTML Tags from the name and title-cases it. Filters that accept arguments have parentheses around the arguments, like a function call. This example will join a list by commas: {{ list|join(', ') }}.

The List of Builtin Filters below describes all the builtin filters.

Tests

Beside filters there are also so called “tests” available. Tests can be used to test a variable against a common expression. To test a variable or expression you add is plus the name of the test after the variable. For example to find out if a variable is defined you can do name is defined which will then return true or false depending on if name is defined.

Tests can accept arguments too. If the test only takes one argument you can leave out the parentheses to group them. For example the following two expressions do the same:

{% if loop.index is divisibleby 3 %}
{% if loop.index is divisibleby(3) %}

The List of Builtin Tests below describes all the builtin tests.

Comments

To comment-out part of a line in a template, use the comment syntax which is by default set to {# ... #}. This is useful to comment out parts of the template for debugging or to add information for other template designers or yourself:

{# note: disabled template because we no longer use this
    {% for user in users %}
        ...
    {% endfor %}
#}

Whitespace Control

In the default configuration, a single trailing newline is stripped if present, and whitespace is not further modified by the template engine. Each whitespace (spaces, tabs, newlines etc.) is returned unchanged. If the application configures Jinja to trim_blocks the first newline after a template tag is removed automatically (like in PHP). The lstrip_blocks option can also be set to strip tabs and spaces from the beginning of line to the start of a block. (Nothing will be stripped if there are other characters before the start of the block.)

With both trim_blocks and lstrip_blocks enabled you can put block tags on their own lines, and the entire block line will be removed when rendered, preserving the whitespace of the contents. For example, without the trim_blocks and lstrip_blocks options, this template:

<div>
    {% if True %}
        yay
    {% endif %}
</div>

gets rendered with blank lines inside the div:

<div>

        yay

</div>

But with both trim_blocks and lstrip_blocks enabled, the lines with the template blocks are removed while preserving the whitespace of the contents:

<div>
        yay
</div>

You can manually disable the lstrip_blocks behavior by putting a plus sign (+) at the start of a block:

<div>
        {%+ if something %}yay{% endif %}
</div>

You can also strip whitespace in templates by hand. If you put an minus sign (-) to the start or end of an block (for example a for tag), a comment or variable expression you can remove the whitespaces after or before that block:

{% for item in seq -%}
    {{ item }}
{%- endfor %}

This will yield all elements without whitespace between them. If seq was a list of numbers from 1 to 9 the output would be 123456789.

If Line Statements are enabled they strip leading whitespace automatically up to the beginning of the line.

Jinja2 by default also removes trailing newlines. To keep the single trailing newline when it is present, configure Jinja to keep_trailing_newline.

Note

You must not use a whitespace between the tag and the minus sign.

valid:

{%- if foo -%}...{% endif %}

invalid:

{% - if foo - %}...{% endif %}

Escaping

It is sometimes desirable or even necessary to have Jinja ignore parts it would otherwise handle as variables or blocks. For example if the default syntax is used and you want to use {{ as raw string in the template and not start a variable you have to use a trick.

The easiest way is to output the variable delimiter ({{) by using a variable expression:

{{ '{{' }}

For bigger sections it makes sense to mark a block raw. For example to put Jinja syntax as example into a template you can use this snippet:

{% raw %}
    <ul>
    {% for item in seq %}
        <li>{{ item }}</li>
    {% endfor %}
    </ul>
{% endraw %}

Line Statements

If line statements are enabled by the application it’s possible to mark a line as a statement. For example if the line statement prefix is configured to # the following two examples are equivalent:

<ul>
# for item in seq
    <li>{{ item }}</li>
# endfor
</ul>

<ul>
{% for item in seq %}
    <li>{{ item }}</li>
{% endfor %}
</ul>

The line statement prefix can appear anywhere on the line as long as no text precedes it. For better readability statements that start a block (such as for, if, elif etc.) may end with a colon:

# for item in seq:
    ...
# endfor

Note

Line statements can span multiple lines if there are open parentheses, braces or brackets:

<ul>
# for href, caption in [('index.html', 'Index'),
                        ('about.html', 'About')]:
    <li><a href="{{ href }}">{{ caption }}</a></li>
# endfor
</ul>

Since Jinja 2.2 line-based comments are available as well. For example if the line-comment prefix is configured to be ## everything from ## to the end of the line is ignored (excluding the newline sign):

# for item in seq:
    <li>{{ item }}</li>     ## this comment is ignored
# endfor

Template Inheritance

The most powerful part of Jinja is template inheritance. Template inheritance allows you to build a base “skeleton” template that contains all the common elements of your site and defines blocks that child templates can override.

Sounds complicated but is very basic. It’s easiest to understand it by starting with an example.

Base Template

This template, which we’ll call base.html, defines a simple HTML skeleton document that you might use for a simple two-column page. It’s the job of “child” templates to fill the empty blocks with content:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    {% block head %}
    <link rel="stylesheet" href="style.css" />
    <title>{% block title %}{% endblock %} - My Webpage</title>
    {% endblock %}
</head>
<body>
    <div id="content">{% block content %}{% endblock %}</div>
    <div id="footer">
        {% block footer %}
        &copy; Copyright 2008 by <a href="http://domain.invalid/">you</a>.
        {% endblock %}
    </div>
</body>

In this example, the {% block %} tags define four blocks that child templates can fill in. All the block tag does is to tell the template engine that a child template may override those portions of the template.

Child Template

A child template might look like this:

{% extends "base.html" %}
{% block title %}Index{% endblock %}
{% block head %}
    {{ super() }}
    <style type="text/css">
        .important { color: #336699; }
    </style>
{% endblock %}
{% block content %}
    <h1>Index</h1>
    <p class="important">
      Welcome on my awesome homepage.
    </p>
{% endblock %}

The {% extends %} tag is the key here. It tells the template engine that this template “extends” another template. When the template system evaluates this template, first it locates the parent. The extends tag should be the first tag in the template. Everything before it is printed out normally and may cause confusion. For details about this behavior and how to take advantage of it, see Null-Master Fallback.

The filename of the template depends on the template loader. For example the FileSystemLoader allows you to access other templates by giving the filename. You can access templates in subdirectories with a slash:

{% extends "layout/default.html" %}

But this behavior can depend on the application embedding Jinja. Note that since the child template doesn’t define the footer block, the value from the parent template is used instead.

You can’t define multiple {% block %} tags with the same name in the same template. This limitation exists because a block tag works in “both” directions. That is, a block tag doesn’t just provide a hole to fill - it also defines the content that fills the hole in the parent. If there were two similarly-named {% block %} tags in a template, that template’s parent wouldn’t know which one of the blocks’ content to use.

If you want to print a block multiple times you can however use the special self variable and call the block with that name:

<title>{% block title %}{% endblock %}</title>
<h1>{{ self.title() }}</h1>
{% block body %}{% endblock %}

Super Blocks

It’s possible to render the contents of the parent block by calling super. This gives back the results of the parent block:

{% block sidebar %}
    <h3>Table Of Contents</h3>
    ...
    {{ super() }}
{% endblock %}

Named Block End-Tags

Jinja2 allows you to put the name of the block after the end tag for better readability:

{% block sidebar %}
    {% block inner_sidebar %}
        ...
    {% endblock inner_sidebar %}
{% endblock sidebar %}

However the name after the endblock word must match the block name.

Block Nesting and Scope

Blocks can be nested for more complex layouts. However per default blocks may not access variables from outer scopes:

{% for item in seq %}
    <li>{% block loop_item %}{{ item }}{% endblock %}</li>
{% endfor %}

This example would output empty <li> items because item is unavailable inside the block. The reason for this is that if the block is replaced by a child template a variable would appear that was not defined in the block or passed to the context.

Starting with Jinja 2.2 you can explicitly specify that variables are available in a block by setting the block to “scoped” by adding the scoped modifier to a block declaration:

{% for item in seq %}
    <li>{% block loop_item scoped %}{{ item }}{% endblock %}</li>
{% endfor %}

When overriding a block the scoped modifier does not have to be provided.

Template Objects

Changed in version 2.4.

If a template object was passed to the template context you can extend from that object as well. Assuming the calling code passes a layout template as layout_template to the environment, this code works:

{% extends layout_template %}

Previously the layout_template variable had to be a string with the layout template’s filename for this to work.

HTML Escaping

When generating HTML from templates, there’s always a risk that a variable will include characters that affect the resulting HTML. There are two approaches: manually escaping each variable or automatically escaping everything by default.

Jinja supports both, but what is used depends on the application configuration. The default configuaration is no automatic escaping for various reasons:

  • escaping everything except of safe values will also mean that Jinja is escaping variables known to not include HTML such as numbers which is a huge performance hit.
  • The information about the safety of a variable is very fragile. It could happen that by coercing safe and unsafe values the return value is double escaped HTML.

Working with Manual Escaping

If manual escaping is enabled it’s your responsibility to escape variables if needed. What to escape? If you have a variable that may include any of the following chars (>, <, &, or ") you have to escape it unless the variable contains well-formed and trusted HTML. Escaping works by piping the variable through the |e filter: {{ user.username|e }}.

Working with Automatic Escaping

When automatic escaping is enabled everything is escaped by default except for values explicitly marked as safe. Those can either be marked by the application or in the template by using the |safe filter. The main problem with this approach is that Python itself doesn’t have the concept of tainted values so the information if a value is safe or unsafe can get lost. If the information is lost escaping will take place which means that you could end up with double escaped contents.

Double escaping is easy to avoid however, just rely on the tools Jinja2 provides and don’t use builtin Python constructs such as the string modulo operator.

Functions returning template data (macros, super, self.BLOCKNAME) return safe markup always.

String literals in templates with automatic escaping are considered unsafe too. The reason for this is that the safe string is an extension to Python and not every library will work properly with it.

List of Control Structures

A control structure refers to all those things that control the flow of a program - conditionals (i.e. if/elif/else), for-loops, as well as things like macros and blocks. Control structures appear inside {% ... %} blocks in the default syntax.

For

Loop over each item in a sequence. For example, to display a list of users provided in a variable called users:

<h1>Members</h1>
<ul>
{% for user in users %}
  <li>{{ user.username|e }}</li>
{% endfor %}
</ul>

As variables in templates retain their object properties, it is possible to iterate over containers like dict:

<dl>
{% for key, value in my_dict.iteritems() %}
    <dt>{{ key|e }}</dt>
    <dd>{{ value|e }}</dd>
{% endfor %}
</dl>

Note however that dictionaries usually are unordered so you might want to either pass it as a sorted list to the template or use the dictsort filter.

Inside of a for-loop block you can access some special variables:

Variable Description
loop.index The current iteration of the loop. (1 indexed)
loop.index0 The current iteration of the loop. (0 indexed)
loop.revindex The number of iterations from the end of the loop (1 indexed)
loop.revindex0 The number of iterations from the end of the loop (0 indexed)
loop.first True if first iteration.
loop.last True if last iteration.
loop.length The number of items in the sequence.
loop.cycle A helper function to cycle between a list of sequences. See the explanation below.
loop.depth Indicates how deep in deep in a recursive loop the rendering currently is. Starts at level 1
loop.depth0 Indicates how deep in deep in a recursive loop the rendering currently is. Starts at level 0

Within a for-loop, it’s possible to cycle among a list of strings/variables each time through the loop by using the special loop.cycle helper:

{% for row in rows %}
    <li class="{{ loop.cycle('odd', 'even') }}">{{ row }}</li>
{% endfor %}

Since Jinja 2.1 an extra cycle helper exists that allows loop-unbound cycling. For more information have a look at the List of Global Functions.

Unlike in Python it’s not possible to break or continue in a loop. You can however filter the sequence during iteration which allows you to skip items. The following example skips all the users which are hidden:

{% for user in users if not user.hidden %}
    <li>{{ user.username|e }}</li>
{% endfor %}

The advantage is that the special loop variable will count correctly thus not counting the users not iterated over.

If no iteration took place because the sequence was empty or the filtering removed all the items from the sequence you can render a replacement block by using else:

<ul>
{% for user in users %}
    <li>{{ user.username|e }}</li>
{% else %}
    <li><em>no users found</em></li>
{% endfor %}
</ul>

Note that in Python else blocks are executed whenever the corresponding loop did not break. Since in Jinja loops cannot break anyway, a slightly different behavior of the else keyword was chosen.

It is also possible to use loops recursively. This is useful if you are dealing with recursive data such as sitemaps. To use loops recursively you basically have to add the recursive modifier to the loop definition and call the loop variable with the new iterable where you want to recurse.

The following example implements a sitemap with recursive loops:

<ul class="sitemap">
{%- for item in sitemap recursive %}
    <li><a href="{{ item.href|e }}">{{ item.title }}</a>
    {%- if item.children -%}
        <ul class="submenu">{{ loop(item.children) }}</ul>
    {%- endif %}</li>
{%- endfor %}
</ul>

The loop variable always refers to the closest (innermost) loop. If we have more than one levels of loops, we can rebind the variable loop by writing {% set outer_loop = loop %} after the loop that we want to use recursively. Then, we can call it using {{ outer_loop(...) }}

If

The if statement in Jinja is comparable with the if statements of Python. In the simplest form you can use it to test if a variable is defined, not empty or not false:

{% if users %}
<ul>
{% for user in users %}
    <li>{{ user.username|e }}</li>
{% endfor %}
</ul>
{% endif %}

For multiple branches elif and else can be used like in Python. You can use more complex Expressions there too:

{% if kenny.sick %}
    Kenny is sick.
{% elif kenny.dead %}
    You killed Kenny!  You bastard!!!
{% else %}
    Kenny looks okay --- so far
{% endif %}

If can also be used as inline expression and for loop filtering.

Macros

Macros are comparable with functions in regular programming languages. They are useful to put often used idioms into reusable functions to not repeat yourself.

Here a small example of a macro that renders a form element:

{% macro input(name, value='', type='text', size=20) -%}
    <input type="{{ type }}" name="{{ name }}" value="{{
        value|e }}" size="{{ size }}">
{%- endmacro %}

The macro can then be called like a function in the namespace:

<p>{{ input('username') }}</p>
<p>{{ input('password', type='password') }}</p>

If the macro was defined in a different template you have to import it first.

Inside macros you have access to three special variables:

varargs
If more positional arguments are passed to the macro than accepted by the macro they end up in the special varargs variable as list of values.
kwargs
Like varargs but for keyword arguments. All unconsumed keyword arguments are stored in this special variable.
caller
If the macro was called from a call tag the caller is stored in this variable as macro which can be called.

Macros also expose some of their internal details. The following attributes are available on a macro object:

name
The name of the macro. {{ input.name }} will print input.
arguments
A tuple of the names of arguments the macro accepts.
defaults
A tuple of default values.
catch_kwargs
This is true if the macro accepts extra keyword arguments (ie: accesses the special kwargs variable).
catch_varargs
This is true if the macro accepts extra positional arguments (ie: accesses the special varargs variable).
caller
This is true if the macro accesses the special caller variable and may be called from a call tag.

If a macro name starts with an underscore it’s not exported and can’t be imported.

Call

In some cases it can be useful to pass a macro to another macro. For this purpose you can use the special call block. The following example shows a macro that takes advantage of the call functionality and how it can be used:

{% macro render_dialog(title, class='dialog') -%}
    <div class="{{ class }}">
        <h2>{{ title }}</h2>
        <div class="contents">
            {{ caller() }}
        </div>
    </div>
{%- endmacro %}

{% call render_dialog('Hello World') %}
    This is a simple dialog rendered by using a macro and
    a call block.
{% endcall %}

It’s also possible to pass arguments back to the call block. This makes it useful as replacement for loops. Generally speaking a call block works exactly like an macro, just that it doesn’t have a name.

Here an example of how a call block can be used with arguments:

{% macro dump_users(users) -%}
    <ul>
    {%- for user in users %}
        <li><p>{{ user.username|e }}</p>{{ caller(user) }}</li>
    {%- endfor %}
    </ul>
{%- endmacro %}

{% call(user) dump_users(list_of_user) %}
    <dl>
        <dl>Realname</dl>
        <dd>{{ user.realname|e }}</dd>
        <dl>Description</dl>
        <dd>{{ user.description }}</dd>
    </dl>
{% endcall %}

Filters

Filter sections allow you to apply regular Jinja2 filters on a block of template data. Just wrap the code in the special filter section:

{% filter upper %}
    This text becomes uppercase
{% endfilter %}

Assignments

Inside code blocks you can also assign values to variables. Assignments at top level (outside of blocks, macros or loops) are exported from the template like top level macros and can be imported by other templates.

Assignments use the set tag and can have multiple targets:

{% set navigation = [('index.html', 'Index'), ('about.html', 'About')] %}
{% set key, value = call_something() %}

Extends

The extends tag can be used to extend a template from another one. You can have multiple of them in a file but only one of them may be executed at the time. See the section about Template Inheritance above.

Block

Blocks are used for inheritance and act as placeholders and replacements at the same time. They are documented in detail as part of the section about Template Inheritance.

Include

The include statement is useful to include a template and return the rendered contents of that file into the current namespace:

{% include 'header.html' %}
    Body
{% include 'footer.html' %}

Included templates have access to the variables of the active context by default. For more details about context behavior of imports and includes see Import Context Behavior.

From Jinja 2.2 onwards you can mark an include with ignore missing in which case Jinja will ignore the statement if the template to be included does not exist. When combined with with or without context it has to be placed before the context visibility statement. Here some valid examples:

{% include "sidebar.html" ignore missing %}
{% include "sidebar.html" ignore missing with context %}
{% include "sidebar.html" ignore missing without context %}

New in version 2.2.

You can also provide a list of templates that are checked for existence before inclusion. The first template that exists will be included. If ignore missing is given, it will fall back to rendering nothing if none of the templates exist, otherwise it will raise an exception.

Example:

{% include ['page_detailed.html', 'page.html'] %}
{% include ['special_sidebar.html', 'sidebar.html'] ignore missing %}

Changed in version 2.4: If a template object was passed to the template context you can include that object using include.

Import

Jinja2 supports putting often used code into macros. These macros can go into different templates and get imported from there. This works similar to the import statements in Python. It’s important to know that imports are cached and imported templates don’t have access to the current template variables, just the globals by default. For more details about context behavior of imports and includes see Import Context Behavior.

There are two ways to import templates. You can import the complete template into a variable or request specific macros / exported variables from it.

Imagine we have a helper module that renders forms (called forms.html):

{% macro input(name, value='', type='text') -%}
    <input type="{{ type }}" value="{{ value|e }}" name="{{ name }}">
{%- endmacro %}

{%- macro textarea(name, value='', rows=10, cols=40) -%}
    <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
        }}">{{ value|e }}</textarea>
{%- endmacro %}

The easiest and most flexible is importing the whole module into a variable. That way you can access the attributes:

{% import 'forms.html' as forms %}
<dl>
    <dt>Username</dt>
    <dd>{{ forms.input('username') }}</dd>
    <dt>Password</dt>
    <dd>{{ forms.input('password', type='password') }}</dd>
</dl>
<p>{{ forms.textarea('comment') }}</p>

Alternatively you can import names from the template into the current namespace:

{% from 'forms.html' import input as input_field, textarea %}
<dl>
    <dt>Username</dt>
    <dd>{{ input_field('username') }}</dd>
    <dt>Password</dt>
    <dd>{{ input_field('password', type='password') }}</dd>
</dl>
<p>{{ textarea('comment') }}</p>

Macros and variables starting with one or more underscores are private and cannot be imported.

Changed in version 2.4: If a template object was passed to the template context you can import from that object.

Import Context Behavior

Per default included templates are passed the current context and imported templates not. The reason for this is that imports unlike includes are cached as imports are often used just as a module that holds macros.

This however can be changed of course explicitly. By adding with context or without context to the import/include directive the current context can be passed to the template and caching is disabled automatically.

Here two examples:

{% from 'forms.html' import input with context %}
{% include 'header.html' without context %}

Note

In Jinja 2.0 the context that was passed to the included template did not include variables defined in the template. As a matter of fact this did not work:

{% for box in boxes %}
    {% include "render_box.html" %}
{% endfor %}

The included template render_box.html is not able to access box in Jinja 2.0. As of Jinja 2.1 render_box.html is able to do so.

Expressions

Jinja allows basic expressions everywhere. These work very similar to regular Python and even if you’re not working with Python you should feel comfortable with it.

Literals

The simplest form of expressions are literals. Literals are representations for Python objects such as strings and numbers. The following literals exist:

“Hello World”:
Everything between two double or single quotes is a string. They are useful whenever you need a string in the template (for example as arguments to function calls, filters or just to extend or include a template).
42 / 42.23:
Integers and floating point numbers are created by just writing the number down. If a dot is present the number is a float, otherwise an integer. Keep in mind that for Python 42 and 42.0 is something different.
[‘list’, ‘of’, ‘objects’]:

Everything between two brackets is a list. Lists are useful to store sequential data in or to iterate over them. For example you can easily create a list of links using lists and tuples with a for loop:

<ul>
{% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
                         ('downloads.html', 'Downloads')] %}
    <li><a href="{{ href }}">{{ caption }}</a></li>
{% endfor %}
</ul>
(‘tuple’, ‘of’, ‘values’):
Tuples are like lists, just that you can’t modify them. If the tuple only has one item you have to end it with a comma. Tuples are usually used to represent items of two or more elements. See the example above for more details.
{‘dict’: ‘of’, ‘key’: ‘and’, ‘value’: ‘pairs’}:
A dict in Python is a structure that combines keys and values. Keys must be unique and always have exactly one value. Dicts are rarely used in templates, they are useful in some rare cases such as the xmlattr() filter.
true / false:
true is always true and false is always false.

Note

The special constants true, false and none are indeed lowercase. Because that caused confusion in the past, when writing True expands to an undefined variable that is considered false, all three of them can be written in title case too (True, False, and None). However for consistency (all Jinja identifiers are lowercase) you should use the lowercase versions.

Math

Jinja allows you to calculate with values. This is rarely useful in templates but exists for completeness’ sake. The following operators are supported:

+
Adds two objects together. Usually the objects are numbers but if both are strings or lists you can concatenate them this way. This however is not the preferred way to concatenate strings! For string concatenation have a look at the ~ operator. {{ 1 + 1 }} is 2.
-
Substract the second number from the first one. {{ 3 - 2 }} is 1.
/
Divide two numbers. The return value will be a floating point number. {{ 1 / 2 }} is {{ 0.5 }}.
//
Divide two numbers and return the truncated integer result. {{ 20 // 7 }} is 2.
%
Calculate the remainder of an integer division. {{ 11 % 7 }} is 4.
*
Multiply the left operand with the right one. {{ 2 * 2 }} would return 4. This can also be used to repeat a string multiple times. {{ '=' * 80 }} would print a bar of 80 equal signs.
**
Raise the left operand to the power of the right operand. {{ 2**3 }} would return 8.

Comparisons

==
Compares two objects for equality.
!=
Compares two objects for inequality.
>
true if the left hand side is greater than the right hand side.
>=
true if the left hand side is greater or equal to the right hand side.
<
true if the left hand side is lower than the right hand side.
<=
true if the left hand side is lower or equal to the right hand side.

Logic

For if statements, for filtering or if expressions it can be useful to combine multiple expressions:

and
Return true if the left and the right operand is true.
or
Return true if the left or the right operand is true.
not
negate a statement (see below).
(expr)
group an expression.

Note

The is and in operators support negation using an infix notation too: foo is not bar and foo not in bar instead of not foo is bar and not foo in bar. All other expressions require a prefix notation: not (foo and bar).

Other Operators

The following operators are very useful but don’t fit into any of the other two categories:

in
Perform sequence / mapping containment test. Returns true if the left operand is contained in the right. {{ 1 in [1, 2, 3] }} would for example return true.
is
Performs a test.
|
Applies a filter.
~
Converts all operands into strings and concatenates them. {{ "Hello " ~ name ~ "!" }} would return (assuming name is 'John') Hello John!.
()
Call a callable: {{ post.render() }}. Inside of the parentheses you can use positional arguments and keyword arguments like in python: {{ post.render(user, full=true) }}.
. / []
Get an attribute of an object. (See Variables)

If Expression

It is also possible to use inline if expressions. These are useful in some situations. For example you can use this to extend from one template if a variable is defined, otherwise from the default layout template:

{% extends layout_template if layout_template is defined else 'master.html' %}

The general syntax is <do something> if <something is true> else <do something else>.

The else part is optional. If not provided the else block implicitly evaluates into an undefined object:

{{ '[%s]' % page.title if page.title }}

List of Builtin Filters

abs(number)

Return the absolute value of the argument.

attr(obj, name)

Get an attribute of an object. foo|attr("bar") works like foo["bar"] just that always an attribute is returned and items are not looked up.

See Notes on subscriptions for more details.

batch(value, linecount, fill_with=None)

A filter that batches items. It works pretty much like slice just the other way round. It returns a list of lists with the given number of items. If you provide a second parameter this is used to fill up missing items. See this example:

<table>
{%- for row in items|batch(3, '&nbsp;') %}
  <tr>
  {%- for column in row %}
    <td>{{ column }}</td>
  {%- endfor %}
  </tr>
{%- endfor %}
</table>
capitalize(s)

Capitalize a value. The first character will be uppercase, all others lowercase.

center(value, width=80)

Centers the value in a field of a given width.

default(value, default_value=u'', boolean=False)

If the value is undefined it will return the passed default value, otherwise the value of the variable:

{{ my_variable|default('my_variable is not defined') }}

This will output the value of my_variable if the variable was defined, otherwise 'my_variable is not defined'. If you want to use default with variables that evaluate to false you have to set the second parameter to true:

{{ ''|default('the string was empty', true) }}
Aliases:d
dictsort(value, case_sensitive=False, by='key')

Sort a dict and yield (key, value) pairs. Because python dicts are unsorted you may want to use this function to order them by either key or value:

{% for item in mydict|dictsort %}
    sort the dict by key, case insensitive

{% for item in mydict|dictsort(true) %}
    sort the dict by key, case sensitive

{% for item in mydict|dictsort(false, 'value') %}
    sort the dict by key, case insensitive, sorted
    normally and ordered by value.
escape(s)

Convert the characters &, <, >, ‘, and ” in string s to HTML-safe sequences. Use this if you need to display text that might contain such characters in HTML. Marks return value as markup string.

Aliases:e
filesizeformat(value, binary=False)

Format the value like a ‘human-readable’ file size (i.e. 13 kB, 4.1 MB, 102 Bytes, etc). Per default decimal prefixes are used (Mega, Giga, etc.), if the second parameter is set to True the binary prefixes are used (Mebi, Gibi).

first(seq)

Return the first item of a sequence.

float(value, default=0.0)

Convert the value into a floating point number. If the conversion doesn’t work it will return 0.0. You can override this default using the first parameter.

forceescape(value)

Enforce HTML escaping. This will probably double escape variables.

format(value, *args, **kwargs)

Apply python string formatting on an object:

{{ "%s - %s"|format("Hello?", "Foo!") }}
    -> Hello? - Foo!
groupby(value, attribute)

Group a sequence of objects by a common attribute.

If you for example have a list of dicts or objects that represent persons with gender, first_name and last_name attributes and you want to group all users by genders you can do something like the following snippet:

<ul>
{% for group in persons|groupby('gender') %}
    <li>{{ group.grouper }}<ul>
    {% for person in group.list %}
        <li>{{ person.first_name }} {{ person.last_name }}</li>
    {% endfor %}</ul></li>
{% endfor %}
</ul>

Additionally it’s possible to use tuple unpacking for the grouper and list:

<ul>
{% for grouper, list in persons|groupby('gender') %}
    ...
{% endfor %}
</ul>

As you can see the item we’re grouping by is stored in the grouper attribute and the list contains all the objects that have this grouper in common.

Changed in version 2.6: It’s now possible to use dotted notation to group by the child attribute of another attribute.

indent(s, width=4, indentfirst=False)

Return a copy of the passed string, each line indented by 4 spaces. The first line is not indented. If you want to change the number of spaces or indent the first line too you can pass additional parameters to the filter:

{{ mytext|indent(2, true) }}
    indent by two spaces and indent the first line too.
int(value, default=0)

Convert the value into an integer. If the conversion doesn’t work it will return 0. You can override this default using the first parameter.

join(value, d=u'', attribute=None)

Return a string which is the concatenation of the strings in the sequence. The separator between elements is an empty string per default, you can define it with the optional parameter:

{{ [1, 2, 3]|join('|') }}
    -> 1|2|3

{{ [1, 2, 3]|join }}
    -> 123

It is also possible to join certain attributes of an object:

{{ users|join(', ', attribute='username') }}

New in version 2.6: The attribute parameter was added.

last(seq)

Return the last item of a sequence.

length(object)

Return the number of items of a sequence or mapping.

Aliases:count
list(value)

Convert the value into a list. If it was a string the returned list will be a list of characters.

lower(s)

Convert a value to lowercase.

map()

Applies a filter on a sequence of objects or looks up an attribute. This is useful when dealing with lists of objects but you are really only interested in a certain value of it.

The basic usage is mapping on an attribute. Imagine you have a list of users but you are only interested in a list of usernames:

Users on this page: {{ users|map(attribute='username')|join(', ') }}

Alternatively you can let it invoke a filter by passing the name of the filter and the arguments afterwards. A good example would be applying a text conversion filter on a sequence:

Users on this page: {{ titles|map('lower')|join(', ') }}

New in version 2.7.

pprint(value, verbose=False)

Pretty print a variable. Useful for debugging.

With Jinja 1.2 onwards you can pass it a parameter. If this parameter is truthy the output will be more verbose (this requires pretty)

random(seq)

Return a random item from the sequence.

reject()

Filters a sequence of objects by appying a test to the object and rejecting the ones with the test succeeding.

Example usage:

{{ numbers|reject("odd") }}

New in version 2.7.

rejectattr()

Filters a sequence of objects by appying a test to an attribute of an object or the attribute and rejecting the ones with the test succeeding.

{{ users|rejectattr("is_active") }}
{{ users|rejectattr("email", "none") }}

New in version 2.7.

replace(s, old, new, count=None)

Return a copy of the value with all occurrences of a substring replaced with a new one. The first argument is the substring that should be replaced, the second is the replacement string. If the optional third argument count is given, only the first count occurrences are replaced:

{{ "Hello World"|replace("Hello", "Goodbye") }}
    -> Goodbye World

{{ "aaaaargh"|replace("a", "d'oh, ", 2) }}
    -> d'oh, d'oh, aaargh
reverse(value)

Reverse the object or return an iterator the iterates over it the other way round.

round(value, precision=0, method='common')

Round the number to a given precision. The first parameter specifies the precision (default is 0), the second the rounding method:

  • 'common' rounds either up or down
  • 'ceil' always rounds up
  • 'floor' always rounds down

If you don’t specify a method 'common' is used.

{{ 42.55|round }}
    -> 43.0
{{ 42.55|round(1, 'floor') }}
    -> 42.5

Note that even if rounded to 0 precision, a float is returned. If you need a real integer, pipe it through int:

{{ 42.55|round|int }}
    -> 43
safe(value)

Mark the value as safe which means that in an environment with automatic escaping enabled this variable will not be escaped.

select()

Filters a sequence of objects by appying a test to the object and only selecting the ones with the test succeeding.

Example usage:

{{ numbers|select("odd") }}
{{ numbers|select("odd") }}

New in version 2.7.

selectattr()

Filters a sequence of objects by appying a test to an attribute of an object and only selecting the ones with the test succeeding.

Example usage:

{{ users|selectattr("is_active") }}
{{ users|selectattr("email", "none") }}

New in version 2.7.

slice(value, slices, fill_with=None)

Slice an iterator and return a list of lists containing those items. Useful if you want to create a div containing three ul tags that represent columns:

<div class="columwrapper">
  {%- for column in items|slice(3) %}
    <ul class="column-{{ loop.index }}">
    {%- for item in column %}
      <li>{{ item }}</li>
    {%- endfor %}
    </ul>
  {%- endfor %}
</div>

If you pass it a second argument it’s used to fill missing values on the last iteration.

sort(value, reverse=False, case_sensitive=False, attribute=None)

Sort an iterable. Per default it sorts ascending, if you pass it true as first argument it will reverse the sorting.

If the iterable is made of strings the third parameter can be used to control the case sensitiveness of the comparison which is disabled by default.

{% for item in iterable|sort %}
    ...
{% endfor %}

It is also possible to sort by an attribute (for example to sort by the date of an object) by specifying the attribute parameter:

{% for item in iterable|sort(attribute='date') %}
    ...
{% endfor %}

Changed in version 2.6: The attribute parameter was added.

string(object)

Make a string unicode if it isn’t already. That way a markup string is not converted back to unicode.

striptags(value)

Strip SGML/XML tags and replace adjacent whitespace by one space.

sum(iterable, attribute=None, start=0)

Returns the sum of a sequence of numbers plus the value of parameter ‘start’ (which defaults to 0). When the sequence is empty it returns start.

It is also possible to sum up only certain attributes:

Total: {{ items|sum(attribute='price') }}

Changed in version 2.6: The attribute parameter was added to allow suming up over attributes. Also the start parameter was moved on to the right.

title(s)

Return a titlecased version of the value. I.e. words will start with uppercase letters, all remaining characters are lowercase.

trim(value)

Strip leading and trailing whitespace.

truncate(s, length=255, killwords=False, end='...')

Return a truncated copy of the string. The length is specified with the first parameter which defaults to 255. If the second parameter is true the filter will cut the text at length. Otherwise it will discard the last word. If the text was in fact truncated it will append an ellipsis sign ("..."). If you want a different ellipsis sign than "..." you can specify it using the third parameter.

{{ "foo bar baz"|truncate(9) }}
    -> "foo ba..."
{{ "foo bar baz"|truncate(9, True) }}
    -> "foo ..."
upper(s)

Convert a value to uppercase.

urlencode(value)

Escape strings for use in URLs (uses UTF-8 encoding). It accepts both dictionaries and regular strings as well as pairwise iterables.

New in version 2.7.

urlize(value, trim_url_limit=None, nofollow=False, target=None)

Converts URLs in plain text into clickable links.

If you pass the filter an additional integer it will shorten the urls to that number. Also a third argument exists that makes the urls “nofollow”:

{{ mytext|urlize(40, true) }}
    links are shortened to 40 chars and defined with rel="nofollow"

If target is specified, the target attribute will be added to the <a> tag:

{{ mytext|urlize(40, target='_blank') }}

Changed in version 2.8+: The target parameter was added.

wordcount(s)

Count the words in that string.

wordwrap(s, width=79, break_long_words=True, wrapstring=None)

Return a copy of the string passed to the filter wrapped after 79 characters. You can override this default using the first parameter. If you set the second parameter to false Jinja will not split words apart if they are longer than width. By default, the newlines will be the default newlines for the environment, but this can be changed using the wrapstring keyword argument.

New in version 2.7: Added support for the wrapstring parameter.

xmlattr(d, autospace=True)

Create an SGML/XML attribute string based on the items in a dict. All values that are neither none nor undefined are automatically escaped:

<ul{{ {'class': 'my_list', 'missing': none,
        'id': 'list-%d'|format(variable)}|xmlattr }}>
...
</ul>

Results in something like this:

<ul class="my_list" id="list-42">
...
</ul>

As you can see it automatically prepends a space in front of the item if the filter returned something unless the second parameter is false.

List of Builtin Tests

callable(object)

Return whether the object is callable (i.e., some kind of function). Note that classes are callable, as are instances with a __call__() method.

defined(value)

Return true if the variable is defined:

{% if variable is defined %}
    value of variable: {{ variable }}
{% else %}
    variable is not defined
{% endif %}

See the default() filter for a simple way to set undefined variables.

divisibleby(value, num)

Check if a variable is divisible by a number.

equalto(value, other)

Check if an object has the same value as another object:

{% if foo.expression is equalto 42 %}
    the foo attribute evaluates to the constant 42
{% endif %}

This appears to be a useless test as it does exactly the same as the == operator, but it can be useful when used together with the selectattr function:

{{ users|selectattr("email", "equalto", "foo@bar.invalid") }}
escaped(value)

Check if the value is escaped.

even(value)

Return true if the variable is even.

iterable(value)

Check if it’s possible to iterate over an object.

lower(value)

Return true if the variable is lowercased.

mapping(value)

Return true if the object is a mapping (dict etc.).

New in version 2.6.

none(value)

Return true if the variable is none.

number(value)

Return true if the variable is a number.

odd(value)

Return true if the variable is odd.

sameas(value, other)

Check if an object points to the same memory address than another object:

{% if foo.attribute is sameas false %}
    the foo attribute really is the `False` singleton
{% endif %}
sequence(value)

Return true if the variable is a sequence. Sequences are variables that are iterable.

string(value)

Return true if the object is a string.

undefined(value)

Like defined() but the other way round.

upper(value)

Return true if the variable is uppercased.

List of Global Functions

The following functions are available in the global scope by default:

range([start], stop[, step])

Return a list containing an arithmetic progression of integers. range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0. When step is given, it specifies the increment (or decrement). For example, range(4) returns [0, 1, 2, 3]. The end point is omitted! These are exactly the valid indices for a list of 4 elements.

This is useful to repeat a template block multiple times for example to fill a list. Imagine you have 7 users in the list but you want to render three empty items to enforce a height with CSS:

<ul>
{% for user in users %}
    <li>{{ user.username }}</li>
{% endfor %}
{% for number in range(10 - users|count) %}
    <li class="empty"><span>...</span></li>
{% endfor %}
</ul>
lipsum(n=5, html=True, min=20, max=100)

Generates some lorem ipsum for the template. Per default five paragraphs with HTML are generated each paragraph between 20 and 100 words. If html is disabled regular text is returned. This is useful to generate simple contents for layout testing.

dict(**items)

A convenient alternative to dict literals. {'foo': 'bar'} is the same as dict(foo='bar').

class cycler(*items)

The cycler allows you to cycle among values similar to how loop.cycle works. Unlike loop.cycle however you can use this cycler outside of loops or over multiple loops.

This is for example very useful if you want to show a list of folders and files, with the folders on top, but both in the same list with alternating row colors.

The following example shows how cycler can be used:

{% set row_class = cycler('odd', 'even') %}
<ul class="browser">
{% for folder in folders %}
  <li class="folder {{ row_class.next() }}">{{ folder|e }}</li>
{% endfor %}
{% for filename in files %}
  <li class="file {{ row_class.next() }}">{{ filename|e }}</li>
{% endfor %}
</ul>

A cycler has the following attributes and methods:

reset()

Resets the cycle to the first item.

next()

Goes one item a head and returns the then current item.

current

Returns the current item.

new in Jinja 2.1

class joiner(sep=', ')

A tiny helper that can be use to “join” multiple sections. A joiner is passed a string and will return that string every time it’s called, except the first time in which situation it returns an empty string. You can use this to join things:

{% set pipe = joiner("|") %}
{% if categories %} {{ pipe() }}
    Categories: {{ categories|join(", ") }}
{% endif %}
{% if author %} {{ pipe() }}
    Author: {{ author() }}
{% endif %}
{% if can_edit %} {{ pipe() }}
    <a href="?action=edit">Edit</a>
{% endif %}

new in Jinja 2.1

Extensions

The following sections cover the built-in Jinja2 extensions that may be enabled by the application. The application could also provide further extensions not covered by this documentation. In that case there should be a separate document explaining the extensions.

i18n

If the i18n extension is enabled it’s possible to mark parts in the template as translatable. To mark a section as translatable you can use trans:

<p>{% trans %}Hello {{ user }}!{% endtrans %}</p>

To translate a template expression — say, using template filters or just accessing an attribute of an object — you need to bind the expression to a name for use within the translation block:

<p>{% trans user=user.username %}Hello {{ user }}!{% endtrans %}</p>

If you need to bind more than one expression inside a trans tag, separate the pieces with a comma (,):

{% trans book_title=book.title, author=author.name %}
This is {{ book_title }} by {{ author }}
{% endtrans %}

Inside trans tags no statements are allowed, only variable tags are.

To pluralize, specify both the singular and plural forms with the pluralize tag, which appears between trans and endtrans:

{% trans count=list|length %}
There is {{ count }} {{ name }} object.
{% pluralize %}
There are {{ count }} {{ name }} objects.
{% endtrans %}

Per default the first variable in a block is used to determine the correct singular or plural form. If that doesn’t work out you can specify the name which should be used for pluralizing by adding it as parameter to pluralize:

{% trans ..., user_count=users|length %}...
{% pluralize user_count %}...{% endtrans %}

It’s also possible to translate strings in expressions. For that purpose three functions exist:

_ gettext: translate a single string - ngettext: translate a pluralizable string - _: alias for gettext

For example you can print a translated string easily this way:

{{ _('Hello World!') }}

To use placeholders you can use the format filter:

{{ _('Hello %(user)s!')|format(user=user.username) }}

For multiple placeholders always use keyword arguments to format as other languages may not use the words in the same order.

Changed in version 2.5.

If newstyle gettext calls are activated (Newstyle Gettext), using placeholders is a lot easier:

{{ gettext('Hello World!') }}
{{ gettext('Hello %(name)s!', name='World') }}
{{ ngettext('%(num)d apple', '%(num)d apples', apples|count) }}

Note that the ngettext function’s format string automatically receives the count as num parameter additionally to the regular parameters.

Expression Statement

If the expression-statement extension is loaded a tag called do is available that works exactly like the regular variable expression ({{ ... }}) just that it doesn’t print anything. This can be used to modify lists:

{% do navigation.append('a string') %}

Loop Controls

If the application enables the Loop Controls it’s possible to use break and continue in loops. When break is reached, the loop is terminated; if continue is reached, the processing is stopped and continues with the next iteration.

Here a loop that skips every second item:

{% for user in users %}
    {%- if loop.index is even %}{% continue %}{% endif %}
    ...
{% endfor %}

Likewise a look that stops processing after the 10th iteration:

{% for user in users %}
    {%- if loop.index >= 10 %}{% break %}{% endif %}
{%- endfor %}

With Statement

New in version 2.3.

If the application enables the With Statement it is possible to use the with keyword in templates. This makes it possible to create a new inner scope. Variables set within this scope are not visible outside of the scope.

With in a nutshell:

{% with %}
    {% set foo = 42 %}
    {{ foo }}           foo is 42 here
{% endwith %}
foo is not visible here any longer

Because it is common to set variables at the beginning of the scope you can do that within the with statement. The following two examples are equivalent:

{% with foo = 42 %}
    {{ foo }}
{% endwith %}

{% with %}
    {% set foo = 42 %}
    {{ foo }}
{% endwith %}

Autoescape Extension

New in version 2.4.

If the application enables the Autoescape Extension one can activate and deactivate the autoescaping from within the templates.

Example:

{% autoescape true %}
    Autoescaping is active within this block
{% endautoescape %}

{% autoescape false %}
    Autoescaping is inactive within this block
{% endautoescape %}

After the endautoescape the behavior is reverted to what it was before.