Template Design

This document describes the syntax and semantics of the expzdee templates and will be most useful as reference.


A template is simply a dynamic passage of text. A template may contain 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 based of Jinja2, and thus 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:

<html lang="en">
    <title>My Webpage</title>
    <ul id="navigation">
    {% for item in navigation %}
        <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
    {% endfor %}

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

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.

Runtime variables

There are two types of variables in use in a template. The first is runtime variables which are local to the template. Changing a runtime variable does not affect the value of a variable outside of the template’s scope. The other type of variable is a experiment variable object, which we will cover in detail below.

Both types of variables may have attributes or elements on them that you can access too.

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.


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.

Form handling

Functions Description
getErrors(name) Return the HTML rendering of the errors associated with the Field with name ‘field’ (only available in Stage Templates).
getField(name) Return the HTML rendering of the input specified by the Field with name ‘name’ (only available in Stage Templates).
getForm() Return the HTML rendering of all the Fields added to the current stage (only available in Stage Templates).
getLabel(name) Return the HTML rendering of the label specified by the Field with name ‘name’ (only available in Stage Templates).

Experiment variable objects

To retreive a Experimental variable object to be manipulated within a template there is a battery of functions available.

Functions Description
getVar(varName, subject= subjectName, group= groupName)

Return the Variable object with the name varName.

If the Variable object is of scope type ‘group’, the Variable object belonging to the Group specified in the groupName argument is returned. If the groupName argument is not given, but the subjectName argument is, it will return the Variable object that belongs to the Subject’s primary Group. If neither argument is given it will return the Variable object belonging to the primary Group of the Subject/Admin’s currently rendering the template.

If the Variable object is of scope type ‘user’, the Variable object belonging to the Subject/Admin specified in the subjectName argument is returned. If the subjectName argument is not given, it returns the Variable object belonging to the Subject/Admin’s currently rendering the template.


Return a list of Variables.

If the ‘scope’ argument is not supplied it will return it will return all Variables that has a Global scope, it will also return all Variables that belongs to the Group specified in the ‘group’ argument. If the ‘group’ argument is not supplied, but the ‘subject’ argument is, then the Variables belonging to the primary Group of the Subject supplied will be returned. If neither of the two arguments are supplied, then it will return the Variables belonging to the primary Group of the Subject/Admin currently rendering the template.

If the ‘scope’ argument is supplied only the ‘global’, ‘group’ or ‘user’ portion of the above will be returned.


Return a list of all Variables that matches the arguments, a non-supplied argument is treated as a wildcard.

  • ‘names’ can either be a name of a Variable or a list of names of Variables
  • ‘subjects’ can either be a Subject, or as a list of Subject
  • ‘groups’ can either be a Group, or as a list of Group

If no ‘names’ argument is supplied, all Variables of scope type Global will be returned, as well as all Group scoped Variables that belong to a Group in ‘groups’, and lastly all User scoped Variables that belong to a Subject/Admin in ‘subjects’.

If the ‘names’ argument is supplied the Variables and neither the ‘subject’ or ‘group’ argument is supplied it returns all Variables, and if either is specified it will only return those matching the ‘users’ or ‘groups’ specified.


Experiment variable objects can be manipulated with the following methods.

Methods Description
.get() Return the value of the variable object
.getGroup() Return the Group object if the variable object has scope type equal to ‘group’, otherwise ‘None’.
.getName() Return the name of the variable object
.getScope() Return the scope type of the variable object
.getSubject() Return the Subject object if the variable object has scope type is ‘user’, otherwise ‘None’
.getType() Return the data type of the variable object. Either ‘int’, ‘float’, ‘string’, ‘choice’ or ‘list’.
.set(newValue) Sets the variable object to newValue.

In addition if the Experiment variable object is of data type ‘choice’ the following methods also apply.

Methods Description
.getChoices() Return a list of the available strings to choose from for the given variable object.
.set(newValue) Sets the variable object to newValue, but only if newValue is a value in the list of choices.

In addition if the Experiment variable object is of data type ‘int’ or ‘float’ the following methods also apply.

Methods Description
.inc() Increase the value of the variable object by 1.
.dec() Decrease the value of the variable object by 1.

Experiment variable objects may also be set directly using.

Functions Description

Set the value of the Variable specified by ‘variable’, which either is the name of the variable or a Variable, to ‘value’.

If the Variable is of scope type ‘group’ and a Group is passed as the ‘group’ argument, it will set the Variable belonging to this Group. If no ‘group’ argument is given, but a Subject/Admin is specified in the ‘subject’ argument, the Variable belonging to her primary Group is set. If neither of the two are specified, the Variable that belongs to the primary Group of the Subject/Admin currently rendering the template is set.

If the Variable is of scope type ‘user’ and a Subject/Admin is passed as the ‘subject’ argument, the Variable belonging to this Subject/Admin will be set. If no ‘user’ argument is given the Variable belonging the Subject/Admin currently rendering the template is set.


Subject objects can either be retrieved from Variable or Group objects or using the follwing functions.

Functions Description
getSubjects() Return a list of all active Subjets.
getHumanSubjects() Return a list of all active Subjets of type human.
getRobotSubjects() Return a list of all active Subjets of type robot.
getSubject(name) Return a Subject with name ‘name’, or ‘None’ if it can not be found.
getAllSubjects() Return a list of all Subjects, active or not.

The Subject object have the following methods.

Methods Description
.activate() If deactivated, activates a Subject.
.deactivate() If active, deactivate a Subject. A deactivated subject do not show up on getSubjects() calls.
.getEra() Return the Era (experiment or group-wide) that this Subject is ready to enter (may be the current).
.getGroups() Return a list containing all the Groups that the Subject is member of.
.getPrimaryGroup() Return the primary Group for the Subject.
.isActive() Return a boolean indicating whether the Subject is active or not.
.join(group) Make the Subject joins the specified ‘group’.
.leave(group) Make the Subject leave the specified ‘group’.


Group objects can either be retrieved from Variable or Subject objects or using the following functions.

Functions Description
getCurrentGroups() Return a list of all Groups that the current Subject/Admin is member of, that is the Subject/Admin rendering the template.
getCurrentPrimaryGroup() Return the Group that the current Subject/Admin is primary member of, that is the Subject/Admin rendering the template.
getGroup(name) Return a the Groups with name ‘name’, or ‘None’ if it can not be found.
getGroups() Return a list of all Groups

Creates a Group.

If the ‘name’ argument this will be the name of the Group, if not, it will be named ‘group%d’ where ‘%d’ is replaced by the number of Groups incremented by 1.

The Group object have the following methods.

Methods Description
.add(subject) Adds the specified Subject ‘subject’ to the Group.
.remove(subject) Removes the specified ‘subject’ from the Group.
.delete() Delete the Group (and remove any membership in it).
.getEra() Return the current group-level Era.
.getHumanSubjects() Return a list containing all the non-robot Subjects that are member of the Group.
.getRobotSubjects() Return a list containing all the robot Subjects that are member of the Group.
.getSubjects() Return a list containing all the Subjects that are member of the Group.


A Network is either retrieved from the predefined Social Networks of the Experiment or created from scratch at run-time. The nodes of the Network are Subjects. The edges are tuples of the two interlinked Subjects, i.e. to create an edge between the two first subjects we do:

{% set net = getNetwork("Network A") %}
{% set subjects = getSubjects() %}
{% set new_edge = (subjects[0], subjects[1]) %}
{% do net.addEdge(new_edge) %}
Functions Description
getNetwork(name) Return the Network identified by the name ‘name’.
createNetwork() Return an empty Network

The Network object has the following methods:

Methods Description
.getName() Returns the identifying name of the Network
.getSubjects() Return a list of the Subject:s that are nodes in the Network.
.getEdges() Return a list of edges in the Network. An edge is a tuple of the two connected Subject:s
.hasEdge(edge) Return a boolean indicating if the edge ‘edge’ exist in the Network, or not
.hasSubject(subject) Return a boolean indicating if the Subject ‘subject’ exist in the Network, or not
.getNeighbor(subject) Return a list of Subject:s that neighbor the Subject ‘subject’ in the Network
.addSubject(subject) Add Subject ‘subject’ to the Network
.removeSubject(subject) Add Subject ‘subject’ to the Network
.addEdge(edge) Add edge ‘edge’ to the Network
.removeEdge(edge) Remove edge ‘edge’ from the Network


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.


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.


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:

    {% if True %}
    {% endif %}

gets rendered with blank lines inside the 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:


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

        {%+ if something %}yay{% endif %}

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.


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


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


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


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

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

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

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


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

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

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:

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

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; }
{% endblock %}
{% block content %}
    <p class="important">
      Welcome on my awesome homepage.
{% 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.


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

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

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

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

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:

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

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 %}

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(...) }}


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

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.
Like varargs but for keyword arguments. All unconsumed keyword arguments are stored in this special variable.
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:

The name of the macro. {{ input.name }} will print input.
A tuple of the names of arguments the macro accepts.
A tuple of default values.
This is true if the macro accepts extra keyword arguments (ie: accesses the special kwargs variable).
This is true if the macro accepts extra positional arguments (ie: accesses the special varargs variable).
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.


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

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


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 %}


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() %}


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.


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.


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

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


{% 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.


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 %}
    <dd>{{ forms.input('username') }}</dd>
    <dd>{{ forms.input('password', type='password') }}</dd>
<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 %}
    <dd>{{ input_field('username') }}</dd>
    <dd>{{ input_field('password', type='password') }}</dd>
<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 %}


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.


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.


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:

{% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
                         ('downloads.html', 'Downloads')] %}
    <li><a href="{{ href }}">{{ caption }}</a></li>
{% endfor %}
(‘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.


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.


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.


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.


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

Return true if the left and the right operand is true.
Return true if the left or the right operand is true.
negate a statement (see below).
group an expression.


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:

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.
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

List of Builtin Tests

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:

{% for user in users %}
    <li>{{ user.username }}</li>
{% endfor %}
{% for number in range(10 - users|count) %}
    <li class="empty"><span>...</span></li>
{% endfor %}
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.


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 %}

A cycler has the following attributes and methods:


Resets the cycle to the first item.


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


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


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.


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 loopcontrols-extension 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-extension 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.


{% 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.