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Module minijinja::syntax

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Documents the syntax for templates.

Table of Contents

Synopsis

A MiniJinja template is simply a text file. MiniJInja can generate any text-based format (HTML, XML, CSV, LaTeX, etc.). A template doesn’t need to have a specific extension and in fact MiniJinja does not understand much about the file system. However the default configuration for auto escaping uses file extensions to configure the initial behavior.

A template contains expressions, which get replaced with values when a template is rendered; and tags, which control the logic of the template. The template syntax is heavily inspired by Jinja2, Django and Python.

This is a minimal template that illustrates a few basics:

<!doctype html>
<title>{% block title %}My Website{% endblock %}</title>
<ul id="navigation">
{% for item in navigation %}
    <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
{% endfor %}
</ul>

<h1>My Webpage</h1>
{% block body %}{% endblock %}

{# a comment #}

Trailing Newlines

MiniJinja, like Jinja2, will remove one trailing newline from the end of the file automatically on parsing. This lets templates produce a consistent output no matter if the editor adds a trailing newline or not. If one wants a trailing newline an extra newline can be added or the code rendering it adds it manually.

Expressions

MiniJinja allows basic expressions everywhere. These work largely as you expect from Jinja2. Even if you have not used Jinja2 you should feel comfortable with it. To output the result of an expression wrap it in {{ .. }}.

Literals

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

  • "Hello World": Everything between two double or single quotes is a string. They are useful whenever you need a string in the template (e.g. as arguments to function calls and filters, or just to extend or include a template).
  • 42: Integers are whole numbers without a decimal part.
  • 42.0: Floating point numbers can be written using a . as a decimal mark.
  • ['list', 'of', 'objects']: Everything between two brackets is a list. Lists are useful for compatibility with Jinja2 ('list', 'of', 'objects') is also allowed. for storing sequential data to be iterated over.
  • {'map': 'of', 'key': 'and', 'value': 'pairs'}: A map is a structure that combines keys and values. Keys must be unique and always have exactly one value. Maps are rarely created in templates.
  • true / false / none: boolean values and the special none value which maps to the unit type in Rust.

Math

MiniJinja allows you to calculate with values. The following operators are supported:

  • +: Adds two numbers up. {{ 1 + 1 }} is 2.
  • -: Subtract the second number from the first one. {{ 3 - 2 }} is 1.
  • /: Divide two numbers. {{ 1 / 2 }} is 0.5. See note on divisions below.
  • //: Integer divide two numbers. {{ 5 // 3 }} is 1. See note on divisons below.
  • %: Calculate the remainder of an integer division. {{ 11 % 7 }} is 4.
  • *: Multiply the left operand with the right one. {{ 2 * 2 }} would return 4.
  • **: Raise the left operand to the power of the right operand. {{ 2**3 }} would return 8.

Note on divisions: divisions in Jinja2 are flooring, divisions in MiniJinja are at present using euclidean division. They are almost the same but not quite.

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 it can be useful to combine 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): Parentheses group an expression.

Other Operators

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

  • is/is not: Performs a test.
  • in/not in: Performs a containment check.
  • | (pipe, vertical bar): Applies a filter.
  • ~ (tilde): Converts all operands into strings and concatenates them. {{ "Hello " ~ name ~ "!" }} would return (assuming name is set to 'John') Hello John!.
  • (): Call a callable: {{ super() }}. Inside of the parentheses you can use positional arguments. Additionally keyword arguments are supported which are treated like a dict syntax. Eg: foo(a=1, b=2) is the same as foo({"a": 1, "b": 2}).
  • . / []: Get an attribute of an object.

If Expressions

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 'default.html' %}

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

{{ title|upper if title }}

Tags

Tags control logic in templates. The following tags exist:

{% for %}

The for tag loops over each item in a sequence. For example, to display a list of users provided in a variable called users:

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

It’s also possible to unpack tuples while iterating:

<h1>Members</h1>
<ul>
{% for (key, value) in list_of_pairs %}
  <li>{{ key }}: {{ value }}</li>
{% endfor %}
</ul>

Inside of the for block you can access some special variables:

  • 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 this is the first iteration.
  • loop.last: True if this is the 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 a recursive loop the rendering currently is. Starts at level 1
  • loop.depth0: Indicates how 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 %}

Unlike in Rust or 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 }}</li>
{% endfor %}

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

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

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.

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

{% if %}

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

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

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

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

{% extends %}

The extends tag can be used to extend one template from another. You can have multiple extends tags in a file, but only one of them may be executed at a time. For more information see block.

{% block %}

Blocks are used for inheritance and act as both placeholders and replacements at the same time:

The most powerful part of MiniJinja 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.

Base Template:

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

<!doctype html>
{% block head %}
<title>{% block title %}{% endblock %}</title>
{% endblock %}
{% block body %}{% endblock %}

Child Template:

{% extends "base.html" %}
{% block title %}Index{% endblock %}
{% block head %}
  {{ super() }}
  <style type="text/css">
    .important { color: #336699; }
  </style>
{% endblock %}
{% block body %}
  <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 that this template “extends” another template. When the template system evaluates this template, it first locates the parent. The extends tag should be the first tag in the template.

As you can see it’s also possible to render the contents of the parent block by calling super(). 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 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 special self variable and call the block with that name:

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

MiniJinja 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.

{% include #}

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

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

Included templates have access to the variables of the active context.

{% with %}

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

{% filter %}

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

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

{% autoescape %}

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

Example:

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

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

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