Template Designer Documentation¶

This document describes the syntax and semantics of the template engine andwill be most useful as reference to those creating Jinja templates. As thetemplate engine is very flexible, the configuration from the application canbe slightly different from the code presented here in terms of delimiters andbehavior of undefined values.

Synopsis¶

A Jinja template is simply a text file. Jinja can generate any text-basedformat (HTML, XML, CSV, LaTeX, etc.). A Jinja template doesn’t need to have aspecific extension: .html, .xml, or any other extension is just fine.

A template contains variables and/or expressions, which get replacedwith values when a template is rendered; and tags, which control thelogic of the template. The template syntax is heavily inspired by Django andPython.

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

<!DOCTYPE html>
<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 }}
 
    {# a comment #}
</body>
</html>

The following example shows the default configuration settings. An applicationdeveloper can change the syntax configuration from {% foo %} to <% foo %>, or something similar.

There are a few kinds of delimiters. The default Jinja delimiters areconfigured as follows:

{% … %} for Statements
{{ … }} for Expressions to print to the template output
{# … #} for Comments not included in the template output
… ## for Line Statements

Variables¶

Template variables are defined by the context dictionary passed to thetemplate.

You can mess around with the variables in templates provided they are passed inby the application. Variables may have attributes or elements on them you canaccess too. What attributes a variable has depends heavily on the applicationproviding that variable.

You can use a dot (.) to access attributes of a variable in additionto the standard Python getitem “subscript” syntax ([]).

The following lines do the same thing:

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

It’s important to know that the outer double-curly braces are not part of thevariable, but the print statement. If you access variables inside tags don’tput the braces around them.

If a variable or attribute does not exist, you will get back an undefinedvalue. What you can do with that kind of value depends on the applicationconfiguration: the default behavior is to evaluate to an empty string ifprinted or iterated over, and to fail for every other operation.

Implementation

For the sake of convenience, foo.bar in Jinja2 does the followingthings on the Python layer:

check for an attribute called bar on foo(getattr(foo, 'bar'))
if there is not, check for an item 'bar' in foo(foo.getitem('bar'))
if there is not, return an undefined object.
foo['bar'] works mostly the same with a small difference in sequence:
check for an item 'bar' in foo.(foo.getitem('bar'))
if there is not, check for an attribute called bar on foo.(getattr(foo, 'bar'))
if there is not, return an undefined object.
This is important if an object has an item and attribute with the samename. Additionally, the attr() filter only looks up attributes.

Filters¶

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

For example, {{ name|striptags|title }} will remove all HTML Tags fromvariable name and title-case the output (title(striptags(name))).

Filters that accept arguments have parentheses around the arguments, just likea function call. For example: {{ listx|join(', ') }} will join a list withcommas (str.join(', ', listx)).

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

Tests¶

Beside filters, there are also so-called “tests” available. Tests can be usedto test a variable against a common expression. To test a variable orexpression, you add is plus the name of the test after the variable. Forexample, to find out if a variable is defined, you can do name is defined,which will then return true or false depending on whether name is definedin the current template context.

Tests can accept arguments, too. If the test only takes one argument, you canleave out the parentheses. For example, the following twoexpressions do the same thing:

{% 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 isby default set to {# … #}. This is useful to comment out parts of thetemplate for debugging or to add information for other template designers oryourself:

{# note: commented-out 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
other whitespace (spaces, tabs, newlines etc.) is returned unchanged
If an application configures Jinja to trim_blocks, the first newline after atemplate tag is removed automatically (like in PHP). The _lstrip_blocks_option can also be set to strip tabs and spaces from the beginning of aline to the start of a block. (Nothing will be stripped if there areother characters before the start of the block.)

With both trim_blocks and lstrip_blocks enabled, you can put block tagson their own lines, and the entire block line will be removed whenrendered, 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 template blocklines are removed and other whitespace is preserved:

<div>
        yay
</div>

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

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

You can also strip whitespace in templates by hand. If you add a minussign (-) to the start or end of a block (e.g. a For tag), acomment, or a variable expression, the whitespaces before or afterthat block will be removed:

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

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

If Line Statements are enabled, they strip leading whitespaceautomatically up to the beginning of the line.

By default, Jinja2 also removes trailing newlines. To keep singletrailing newlines, configure Jinja to keep_trailing_newline.

Note

You must not add whitespace between the tag and the minus sign.

valid:

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

invalid:

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

Escaping¶

It is sometimes desirable – even necessary – to have Jinja ignore partsit would otherwise handle as variables or blocks. For example, if, withthe default syntax, you want to use {{ as a raw string in a template andnot start a variable, you have to use a trick.

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

{{ '{{' }}

For bigger sections, it makes sense to mark a block raw. For example, toinclude example Jinja syntax in 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 aline as a statement. For example, if the line statement prefix is configuredto #, 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 textprecedes it. For better readability, statements that start a block (such asfor, 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, ifthe line-comment prefix is configured to be ##, everything from ## tothe 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 inheritanceallows you to build a base “skeleton” template that contains all the commonelements of your site and defines blocks that child templates can override.

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

Base Template¶

This template, which we’ll call base.html, defines a simple HTML skeletondocument 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>
<html lang="en">
<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>
</html>

In this example, the {% block %} tags define four blocks that child templatescan fill in. All the block tag does is tell the template engine that achild template may override those placeholders in 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 to my awesome homepage.
    </p>
{% endblock %}

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

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

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

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

You can’t define multiple {% block %} tags with the same name in thesame template. This limitation exists because a block tag works in “both”directions. That is, a block tag doesn’t just provide a placeholder to fill- it also defines the content that fills the placeholder 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 specialself 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 betterreadability:

{% 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 blocksmay 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 unavailableinside the block. The reason for this is that if the block is replaced bya child template, a variable would appear that was not defined in the block orpassed to the context.

Starting with Jinja 2.2, you can explicitly specify that variables areavailable 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 in the template context, you canextend from that object as well. Assuming the calling code passesa layout template as layout_template to the environment, thiscode works:

{% extends layout_template %}

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

HTML Escaping¶

When generating HTML from templates, there’s always a risk that a variable willinclude characters that affect the resulting HTML. There are two approaches:

manually escaping each variable; or
automatically escaping everything by default.

Jinja supports both. What is used depends on the application configuration.The default configuration is no automatic escaping; for various reasons:

Escaping everything except for safe values will also mean that Jinja isescaping variables known to not include HTML (e.g. numbers, booleans)which can be a huge performance hit.

The information about the safety of a variable is very fragile. It couldhappen that by coercing safe and unsafe values, the return value isdouble-escaped HTML.

Working with Manual Escaping¶

If manual escaping is enabled, it’s your responsibility to escapevariables if needed. What to escape? If you have a variable that _may_include any of the following chars (>, <, &, or ") youSHOULD escape it unless the variable contains well-formed and trustedHTML. 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 exceptfor values explicitly marked as safe. Variables and expressionscan be marked as safe either in:

the context dictionary by the application with MarkupSafe.Markup, or
the template, with the |safe filter

The main problem with this approach is that Python itself doesn’t have theconcept of tainted values; so whether a value is safe or unsafe can get lost.

If a value is not marked safe, auto-escaping will take place; which means thatyou could end up with double-escaped contents. Double-escaping is easy toavoid, however: just rely on the tools Jinja2 provides and don’t use builtinPython constructs such as str.format or the string modulo operator (%).

Jinja2 functions (macros, super, self.BLOCKNAME) always return templatedata that is marked as safe.

String literals in templates with automatic escaping are considered unsafebecause native Python strings (str, unicode, basestring) are notMarkupSafe.Markup strings with an html attribute.

List of Control Structures¶

A control structure refers to all those things that control the flow of aprogram - conditionals (i.e. if/elif/else), for-loops, as well as things likemacros and blocks. With the default syntax, control structures appear inside{% … %} blocks.

For¶

Loop over each item in a sequence. For example, to display a list of usersprovided 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 toiterate 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 Python dicts are not ordered; so you might want toeither pass a sorted list of tuple s – or acollections.OrderedDict – 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 ofsequences. See the explanation below.
loop.depth	Indicates how deep in a recursive loopthe rendering currently is. Starts at level 1
loop.depth0	Indicates how deep in a recursive loopthe rendering currently is. Starts at level 0
loop.previtem	The item from the previous iteration of the loop.Undefined during the first iteration.
loop.nextitem	The item from the following iteration of the loop.Undefined during the last iteration.
loop.changed(val)*	True if previously called with a different value(or not called at all).

Within a for-loop, it’s possible to cycle among a list of strings/variableseach 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-unboundcycling. 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. Youcan, however, filter the sequence during iteration, which allows you to skipitems. 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; thusnot counting the users not iterated over.

If no iteration took place because the sequence was empty or the filteringremoved all the items from the sequence, you can render a default blockby 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 correspondingloop did notbreak. Since 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 aredealing with recursive data such as sitemaps or RDFa.To use loops recursively, you basically have to add the recursive modifierto the loop definition and call the loop variable with the new iterablewhere 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 wehave more than one level of loops, we can rebind the variable loop bywriting {% set outer_loop = loop %} after the loop that we want touse recursively. Then, we can call it using {{ outer_loop(…) }}

Please note that assignments in loops will be cleared at the end of theiteration and cannot outlive the loop scope. Older versions of Jinja2 hada bug where in some circumstances it appeared that assignments would work.This is not supported. See Assignments for more information abouthow to deal with this.

If all you want to do is check whether some value has changed since thelast iteration or will change in the next iteration, you can use previtem_and _nextitem:

{% for value in values %}
    {% if loop.previtem is defined and value > loop.previtem %}
        The value just increased!
    {% endif %}
    {{ value }}
    {% if loop.nextitem is defined and loop.nextitem > value %}
        The value will increase even more!
    {% endif %}
{% endfor %}

If you only care whether the value changed at all, using changed is eveneasier:

{% for entry in entries %}
    {% if loop.changed(entry.category) %}
        <h2>{{ entry.category }}</h2>
    {% endif %}
    <p>{{ entry.message }}</p>
{% endfor %}

If¶

The if statement in Jinja is comparable with the Python if statement.In the simplest form, you can use it to test if a variable is defined, notempty and 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 canuse 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 an inline expression and forloop filtering.

Macros¶

Macros are comparable with functions in regular programming languages. Theyare useful to put often used idioms into reusable functions to not repeatyourself (“DRY”).

Here’s 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 toimport it first.

Inside macros, you have access to three special variables:

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

Macros also expose some of their internal details. The following attributesare 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 (i.e.: accessesthe special kwargs variable).
catch_varargs: This is true if the macro accepts extra positional arguments (i.e.:accesses the special varargs variable).
caller: This is true if the macro accesses the special caller variable and maybe called from a call tag.

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

### Call¶

In some cases it can be useful to pass a macro to another macro. For thispurpose, you can use the special call block. The following example showsa macro that takes advantage of the call functionality and how it can beused:

{% macro renderdialog(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 ituseful as a replacement for loops. Generally speaking, a call block worksexactly like a macro without a name.

Here’s 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 oftemplate 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 attop level (outside of blocks, macros or loops) are exported from the templatelike 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 = callsomething() %}

Scoping Behavior

Please keep in mind that it is not possible to set variables inside ablock and have them show up outside of it. This also applies toloops. The only exception to that rule are if statements which do notintroduce a scope. As a result the following template is not goingto do what you might expect:

{% set iterated = false %}
{% for item in seq %}
{{ item }}
{% set iterated = true %}
{% endfor %}
{% if not iterated %} did not iterate {% endif %}

It is not possible with Jinja syntax to do this. Instead usealternative constructs like the loop else block or the special _loop_variable:

{% for item in seq %}
{{ item }}
{% else %}
did not iterate
{% endfor %}

As of version 2.10 more complex use cases can be handled using namespaceobjects which allow propagating of changes across scopes:

{% set ns = namespace(found=false) %}
{% for item in items %}
{% if item.check_something() %}
{% set ns.found = true %}
{% endif %}
* {{ item.title }}
{% endfor %}
Found item having something: {{ ns.found }}

Note hat the obj.attr notation in the _set tag is only allowed fornamespace objects; attempting to assign an attribute on any other objectwill raise an exception.

New in version 2.10: Added support for namespace objects

### Block Assignments¶

New in version 2.8.

Starting with Jinja 2.8, it’s possible to also use block assignments tocapture the contents of a block into a variable name. This can be usefulin some situations as an alternative for macros. In that case, instead ofusing an equals sign and a value, you just write the variable name and theneverything until {% endset %} is captured.

Example:

{% set navigation %}
    <li><a href="/">Index</a>
    <li><a href="/downloads">Downloads</a>
{% endset %}

The navigation variable then contains the navigation HTML source.

Changed in version 2.10.

Starting with Jinja 2.10, the block assignment supports filters.

Example:

{% set reply | wordwrap %}
    You wrote:
    {{ message }}
{% endset %}

### Extends¶

The extends tag can be used to extend one template from another. You canhave multiple extends tags in a file, but only one of them may be executed ata time.

See the section about Template Inheritance above.

### Blocks¶

Blocks are used for inheritance and act as both placeholders and replacementsat the same time. They are documented in detail in theTemplate Inheritance section.

### Include¶

The include statement is useful to include a template and return therendered 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 bydefault. 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; inwhich case Jinja will ignore the statement if the template to be includeddoes not exist. When combined with with or without context, it mustbe placed before the context visibility statement. Here are some validexamples:

{% 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 existencebefore inclusion. The first template that exists will be included. Ifignore missing is given, it will fall back to rendering nothing ifnone of the templates exist, otherwise it will raise an exception.

Example:

{% include ['pagedetailed.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 caninclude that object using _include.

### Import¶

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

There are two ways to import templates. You can import a complete templateinto 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 way to access a template’s variablesand macros is to import the whole template 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 specific names from a template into the currentnamespace:

{% from 'forms.html' import input as inputfield, 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 andcannot be imported.

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

## Import Context Behavior¶

By default, included templates are passed the current context and importedtemplates are 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 behavior can be changed explicitly: by adding _with context_or _without context to the import/include directive, the current contextcan be passed to the template and caching is disabled automatically.

Here are 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 templatedid not include variables defined in the template. As a matter offact, this did not work:

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

The included template render_box.html is _not able to accessbox in Jinja 2.0. As of Jinja 2.1, renderbox.html _is ableto do so.

## Expressions¶

Jinja allows basic expressions everywhere. These work very similarly toregular Python; even if you’re not working with Pythonyou should feel comfortable with it.

### Literals¶

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

“Hello World”:

Everything between two double or single quotes is a string. They areuseful whenever you need a string in the template (e.g. asarguments to function calls and filters, or just to extend or include atemplate).

42 / 42.23:

Integers and floating point numbers are created by just writing thenumber down. If a dot is present, the number is a float, otherwise aninteger. Keep in mind that, in Python, 42 and 42.0are different (int and float, respectively).

[‘list’, ‘of’, ‘objects’]:

Everything between two brackets is a list. Lists are useful for storingsequential data to be iterated over. For example, you can easilycreate a list of links using lists and tuples for (and 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 that cannot be modified (“immutable”). If a tupleonly has one item, it must be followed by a comma (('1-tuple',)).Tuples are usually used to represent items of two or more elements.See the list example above for more details.

{‘dict’: ‘of’, ‘key’: ‘and’, ‘value’: ‘pairs’}:

A dict in Python is a structure that combines keys and values. Keys mustbe unique and always have exactly one value. Dicts are rarely used intemplates; 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, (True used to expandto an undefined variable that was considered false),all three can now also be written in title case(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 templatesbut exists for completeness’ sake. The following operators are supported:

+: Adds two objects together. Usually the objects are numbers, but if both arestrings or lists, you can concatenate them this way. This, however, is notthe preferred way to concatenate strings! For string concatenation, havea look-see at the ~ operator. {{ 1 + 1 }} is 2.
-: Subtract 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 }}.(Just like from future import division.)

//: 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 }} wouldreturn 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. {{ 23 }}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, and if expressions, it can be useful tocombine multiple expressions:

and: Return true if the left and the right operand are true.
or: Return true if the left or the right operand are 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 barand 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 othertwo categories:

in: Perform a sequence / mapping containment test. Returns true if the leftoperand is contained in the right. {{ 1 in [1, 2, 3] }} would, forexample, return true.
is: Performs a test.
|: Applies a filter.

~: Converts all operands into strings and concatenates them.

{{ "Hello " ~ name ~ "!" }} would return (assuming name is setto 'John') Hello John!.
(): Call a callable: {{ post.render() }}. Inside of the parentheses youcan 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 somesituations. For example, you can use this to extend from one template if avariable 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 implicitlyevaluates into an undefined object:

.. sourcecode:: jinja

{{ ‘[%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 likefoo.bar just that always an attribute is returned and items are notlooked 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 thegiven number of items. If you provide a second parameter thisis used to fill up missing items. See this example:

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

capitalize(_s)¶: Capitalize a value. The first character will be uppercase, all otherslowercase.

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:

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

This will output the value of my_variable if the variable wasdefined, otherwise 'my_variable is not defined'. If you wantto use default with variables that evaluate to false you have toset the second parameter to _true:

{{ ''|default('the string was empty', true) }}

|Aliases:
|——-
|d

dictsort(value, case_sensitive=False, by='key', reverse=False)¶

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

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

{% for item in mydict|dictsort(reverse=true) %}
    sort the dict by key, case insensitive, reverse order

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

{% for item in mydict|dictsort(false, 'value') %}
    sort the dict by value, case insensitive

escape(s)¶: Convert the characters &, <, >, ‘, and ” in string s to HTML-safesequences. Use this if you need to display text that might containsuch 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 binaryprefixes 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 theconversion doesn’t work it will return 0.0. You canoverride 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 personswith gender, first_name and last_name attributes and you want togroup all users by genders you can do something like the followingsnippet:

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

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

<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 grouperin common.

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

indent(s, width=4, first=False, blank=False, indentfirst=None)¶: Return a copy of the string with each line indented by 4 spaces. Thefirst line and blank lines are not indented by default.

|Parameters:
|——-
|
- width – Number of spaces to indent by.
- first – Don’t skip indenting the first line.
- blank – Don’t skip indenting empty lines.

Changed in version 2.10: Blank lines are not indented by default.

Rename the indentfirst argument to first.

int(value, default=0, base=10)¶: Convert the value into an integer. If theconversion doesn’t work it will return 0. You canoverride this default using the first parameter. Youcan also override the default base (10) in the secondparameter, which handles input with prefixes such as0b, 0o and 0x for bases 2, 8 and 16 respectively.The base is ignored for decimal numbers and non-string values.

join(value, d=u'', attribute=None)¶

Return a string which is the concatenation of the strings in thesequence. The separator between elements is an empty string perdefault, 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 listwill 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 reallyonly interested in a certain value of it.

The basic usage is mapping on an attribute. Imagine you have a listof 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 thefilter and the arguments afterwards. A good example would be applying atext conversion filter on a sequence:

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

New in version 2.7.

max(value, case_sensitive=False, attribute=None)¶

Return the largest item from the sequence.

{{ [1, 2, 3]|max }}
    -> 3

|Parameters:
|——-
|
- case_sensitive – Treat upper and lower case strings as distinct.
- attribute – Get the object with the max value of this attribute.

min(value, case_sensitive=False, attribute=None)¶

Return the smallest item from the sequence.

{{ [1, 2, 3]|min }}
    -> 1

|Parameters:
|——-
|
- case_sensitive – Treat upper and lower case strings as distinct.
- attribute – Get the object with the max value of this attribute.

pprint(value, verbose=False)¶: Pretty print a variable. Useful for debugging.

With Jinja 1.2 onwards you can pass it a parameter. If this parameteris 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 applying a test to each object,and rejecting the objects with the test succeeding.

If no test is specified, each object will be evaluated as a boolean.

Example usage:

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

New in version 2.7.

rejectattr()¶

Filters a sequence of objects by applying a test to the specifiedattribute of each object, and rejecting the objects with the testsucceeding.

If no test is specified, the attribute’s value will be evaluated asa boolean.

{{ users|rejectattr("isactive") }}
{{ 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 substringreplaced with a new one. The first argument is the substringthat should be replaced, the second is the replacement string.If the optional third argument count is given, only the firstcount 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 that iterates over it the otherway round.

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

Round the number to a given precision. The firstparameter specifies the precision (default is 0), thesecond 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. Ifyou 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 automaticescaping enabled this variable will not be escaped.

select()¶

Filters a sequence of objects by applying a test to each object,and only selecting the objects with the test succeeding.

If no test is specified, each object will be evaluated as a boolean.

Example usage:

{{ numbers|select("odd") }}
{{ numbers|select("odd") }}
{{ numbers|select("divisibleby", 3) }}
{{ numbers|select("lessthan", 42) }}
{{ strings|select("equalto", "mystring") }}

New in version 2.7.

selectattr()¶

Filters a sequence of objects by applying a test to the specifiedattribute of each object, and only selecting the objects with thetest succeeding.

If no test is specified, the attribute’s value will be evaluated asa boolean.

Example usage:

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

New in version 2.7.

slice(_value, slices, fill_with=None)¶

Slice an iterator and return a list of lists containingthose items. Useful if you want to create a div containingthree 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 missingvalues on the last iteration.

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

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

If the iterable is made of strings the third parameter can be used tocontrol the case sensitiveness of the comparison which is disabled bydefault.

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

It is also possible to sort by an attribute (for example to sortby 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 markupstring 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 returnsstart.

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 overattributes. Also the start parameter was moved on to the right.

title(s)¶: Return a titlecased version of the value. I.e. words will start withuppercase letters, all remaining characters are lowercase.

tojson(value, indent=None)¶: Dumps a structure to JSON so that it’s safe to use in <script>tags. It accepts the same arguments and returns a JSON string. Note thatthis is available in templates through the |tojson filter which willalso mark the result as safe. Due to how this function escapes certaincharacters this is safe even if used outside of <script> tags.

The following characters are escaped in strings:

- <
- >
- &
- '
This makes it safe to embed such strings in any place in HTML with thenotable exception of double quoted attributes. In that case singlequote your attributes or HTML escape it in addition.

The indent parameter can be used to enable pretty printing. Set it tothe number of spaces that the structures should be indented with.

Note that this filter is for use in HTML contexts only.

New in version 2.9.

trim(value)¶: Strip leading and trailing whitespace.

truncate(s, length=255, killwords=False, end='…', leeway=None)¶

Return a truncated copy of the string. The length is specifiedwith the first parameter which defaults to 255. If the secondparameter is true the filter will cut the text at length. Otherwiseit will discard the last word. If the text was in facttruncated it will append an ellipsis sign ("…"). If you want adifferent ellipsis sign than "…" you can specify it using thethird parameter. Strings that only exceed the length by the tolerancemargin given in the fourth parameter will not be truncated.

{{ "foo bar baz qux"|truncate(9) }}
    -> "foo…"
{{ "foo bar baz qux"|truncate(9, True) }}
    -> "foo ba…"
{{ "foo bar baz qux"|truncate(11) }}
    -> "foo bar baz qux"
{{ "foo bar baz qux"|truncate(11, False, '…', 0) }}
    -> "foo bar…"

The default leeway on newer Jinja2 versions is 5 and was 0 before butcan be reconfigured globally.

unique(value, case_sensitive=False, attribute=None)¶

Returns a list of unique items from the the given iterable.

{{ ['foo', 'bar', 'foobar', 'FooBar']|unique }}
    -> ['foo', 'bar', 'foobar']

The unique items are yielded in the same order as their first occurrence inthe iterable passed to the filter.

|Parameters:
|——-
|
- case_sensitive – Treat upper and lower case strings as distinct.
- attribute – Filter objects with unique values for this attribute.

upper(s)¶: Convert a value to uppercase.

urlencode(value)¶: Escape strings for use in URLs (uses UTF-8 encoding). It accepts bothdictionaries and regular strings as well as pairwise iterables.

New in version 2.7.

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

Converts URLs in plain text into clickable links.

If you pass the filter an additional integer it will shorten the urlsto 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 after79 characters. You can override this default using the firstparameter. If you set the second parameter to false Jinja will notsplit words apart if they are longer than width. By default, the newlineswill be the default newlines for the environment, but this can be changedusing 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 automaticallyescaped:

<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 itemif 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 undefinedvariables.

divisibleby(value, num)¶: Check if a variable is divisible by a number.

eq(a, b)¶: |Aliases:
|——-
|==, equalto

escaped(value)¶: Check if the value is escaped.

even(value)¶: Return true if the variable is even.

ge(a, b)¶: |Aliases:
|——-
|>=

gt(a, b)¶: |Aliases:
|——-
|>, greaterthan

in(value, seq)¶: Check if value is in seq.

New in version 2.10.

iterable(value)¶: Check if it’s possible to iterate over an object.

le(a, b)¶: |Aliases:
|——-
|<=

lower(value): Return true if the variable is lowercased.

lt(a, b)¶: |Aliases:
|——-
|<, lessthan

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

New in version 2.6.

ne(a, b)¶: |Aliases:
|——-
|!=

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 anotherobject:

{% 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 variablesthat 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) and range(0, 4, 1) return [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, e.g.to fill a list. Imagine you have 7 users in the list but you want torender 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. By default, five paragraphsof HTML are generated with each paragraph between 20 and 100 words.If html is False, regular text is returned. This is useful to generate simplecontents for layout testing.

dict(**items)¶: A convenient alternative to dict literals. {'foo': 'bar'} is the sameas dict(foo='bar').

class cycler(*items)¶

The cycler allows you to cycle among values similar to how loop.cycle_works. Unlike _loop.cycle, you can use this cycler outside ofloops or over multiple loops.

This can be very useful if you want to show a list of folders andfiles with the folders on top but both in the same list with alternatingrow 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 ahead and returns the then-current item.

current¶: Returns the current item.

New in version 2.1.

class joiner(sep=', ')¶

A tiny helper that can be used to “join” multiple sections. A joiner ispassed a string and will return that string every time it’s called, exceptthe first time (in which case it returns an empty string). You canuse 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 version 2.1.

class namespace(…)¶

Creates a new container that allows attribute assignment using the{% set %} tag:

{% set ns = namespace() %}
{% set ns.foo = 'bar' %}

The main purpose of this is to allow carrying a value from within a loopbody to an outer scope. Initial values can be provided as a dict, askeyword arguments, or both (same behavior as Python’s dict constructor):

{% set ns = namespace(found=false) %}
{% for item in items %}
    {% if item.check_something() %}
        {% set ns.found = true %}
    {% endif %}
    * {{ item.title }}
{% endfor %}
Found item having something: {{ ns.found }}

New in version 2.10.

Extensions¶

The following sections cover the built-in Jinja2 extensions that may beenabled by an application. An application could also provide furtherextensions not covered by this documentation; in which case there shouldbe a separate document explaining said extensions.

i18n¶

If the i18n extension is enabled, it’s possible to mark parts in the templateas 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 by justaccessing an attribute of an object — you need to bind the expression to aname 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, separatethe 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 %}

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

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

When translating longer blocks of text, whitespace and linebreaks result inrather ugly and error-prone translation strings. To avoid this, a trans blockcan be marked as trimmed which will replace all linebreaks and the whitespacesurrounding them with a single space and remove leading/trailing whitespace:

{% trans trimmed book_title=book.title %}
    This is {{ book_title }}.
    You should read it!
{% endtrans %}

If trimming is enabled globally, the notrimmed modifier can be used todisable it for a trans block.

New in version 2.10: The trimmed and notrimmed modifiers have been added.

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 easily print a translated string like this:

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

To use placeholders, 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 (Whitespace Trimming), usingplaceholders 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 receivesthe count as a num parameter in addition to the regular parameters.

Expression Statement¶

If the expression-statement extension is loaded, a tag called do is availablethat works exactly like the regular variable expression ({{ … }}); exceptit 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 touse break and continue in loops. When break is reached, the loop isterminated; if continue is reached, the processing is stopped and continueswith the next iteration.

Here’s a loop that skips every second item:

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

Likewise, a loop that stops processing after the 10th iteration:

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

Note that loop.index starts with 1, and loop.index0 starts with 0(See: For).

With Statement¶

New in version 2.3.

The with statement 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 examplesare equivalent:

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

An important note on scoping here. In Jinja versions before 2.9 thebehavior of referencing one variable to another had some unintendedconsequences. In particular one variable could refer to another definedin the same with block’s opening statement. This caused issues with thecleaned up scoping behavior and has since been improved. In particularin newer Jinja2 versions the following code always refers to the variablea from outside the with block:

{% with a={}, b=a.attribute %}...{% endwith %}

In earlier Jinja versions the b attribute would refer to the results ofthe first attribute. If you depend on this behavior you can rewrite it touse the set tag:

{% with a={} %}
    {% set b = a.attribute %}
{% endwith %}

Extension

In older versions of Jinja (before 2.9) it was required to enable thisfeature with an extension. It’s now enabled by default.

Autoescape Overrides¶

New in version 2.4.

If you want you can activate and deactivate the autoescaping from withinthe templates.

Example:

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

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

Extension

In older versions of Jinja (before 2.9) it was required to enable thisfeature with an extension. It’s now enabled by default.

原文:

http://jinja.pocoo.org/docs/2.10/templates/

Template Designer Documentation

Template Designer Documentation¶

Synopsis¶

… ## for Line Statements

Variables¶

Filters¶

Tests¶

Comments¶

Whitespace Control¶

Escaping¶

Line Statements¶

Template Inheritance¶

Base Template¶

Child Template¶

Super Blocks¶

Named Block End-Tags¶

Block Nesting and Scope¶

Template Objects¶

HTML Escaping¶

Working with Manual Escaping¶

Working with Automatic Escaping¶

List of Control Structures¶

For¶

If¶

Macros¶

Math¶

Comparisons¶

Logic¶

Other Operators¶

If Expression¶

List of Builtin Filters¶

List of Builtin Tests¶

List of Global Functions¶

Extensions¶

i18n¶

Expression Statement¶

Loop Controls¶

With Statement¶

Autoescape Overrides¶