Jinja (template engine)

Jinja is a web template engine for the Python programming language. It was created by Armin Ronacher and is licensed under a BSD License. Jinja is similar to the Django template engine but provides Python-like expressions while ensuring that the templates are evaluated in a sandbox. It is a text-based template language and thus can be used to generate any markup as well as source code.

Jinja
Original author(s)Armin Ronacher
Initial releaseJuly 17, 2008 (2008-07-17)[1]
Stable release
3.1.2[2] Edit this on Wikidata / 28 April 2022 (28 April 2022)
Repository
Written inPython
TypeTemplate engine
LicenseBSD License
Websitepalletsprojects.com/p/jinja/ Edit this on Wikidata

The Jinja template engine allows customization of tags,[3] filters (for formatting or transforming values[4]), tests (for evaluating conditions[4]), and globals.[5] Also, unlike the Django template engine, Jinja allows the template designer to call functions with arguments on objects. Jinja is Flask's default template engine [6] and it is also used by Ansible,[7] Trac, and Salt.[8] It is also used to make SQL macros, for example for use with dbt.[9]

Features

Some of the features of Jinja are:[10]

  • sandboxed execution
  • automatic HTML escaping to prevent cross-site scripting (XSS) attacks
  • template inheritance
  • compiles down to the optimal Python code just-in-time
  • optional ahead-of-time template compilation
  • easy to debug (for example, line numbers of exceptions directly point to the correct line in the template)
  • configurable syntax

Jinja, like Smarty, also ships with an easy-to-use filter system similar to the Unix pipeline.

Syntax

The syntax for printing output in Jinja is using the double curly braces, for example {{ Hello, World! }}.

Statements which set variables in jinja or those which do not have an output can be wrapped within {% and %}, using the set keyword. For example {% set foo = 42 %} sets a variable called foo with a value of 42.

Similar to above, comments in jinja can be written using hashtag (#) instead of a percentage (%), for example, {# helpful comment #}.

The syntax for creating a filter in Jinja is a vertical bar (|), for example {{ variable|filter }}. A variable can have multiple filters, for example {{ variable|filter|filter }}).[4]

The syntax for creating a test in Jinja is the keyword is as well as the conditions for evaluating the validity of a test, such as for example {% if variable is divisibleby 10 %}do something{% endif %}).[4]

For loops can be used to iterate over sequences, while retaining their object properties. The following example demonstrates iterating over a list of users with username and password fields.

{% for user in users %}
    {{ user.username }}
    {{ user.password }}
{% endfor %}

Although break and continue are not allowed inside loops, sequences can be filtered.

Example

Here is a small example of a template file example.html.jinja:[11]

<!DOCTYPE html>
<html>
  <head>
    <title>{{ variable|escape }}</title>
  </head>
  <body>
  {%- for item in item_list %}
    {{ item }}{% if not loop.last %},{% endif %}
  {%- endfor %}
  </body>
</html>

and templating code:

from jinja2 import Template
with open('example.html.jinja') as f:
    tmpl = Template(f.read())
print(tmpl.render(
    variable = 'Value with <unsafe> data',
    item_list = [1, 2, 3, 4, 5, 6]
))

This produces the HTML string:

<!DOCTYPE html>
<html>
  <head>
    <title>Value with &lt;unsafe&gt; data</title>
  </head>
  <body>
    1,
    2,
    3,
    4,
    5,
    6
  </body>
</html>

Sources
  1. "Jinja2 Release History". Retrieved 24 June 2020.
  2. "Release 3.1.2".
  3. "Extensions". Jinja2 Documentation (2.8-dev). Retrieved 2015-05-26.
  4. "Jinja built-in filters and tests (like Django filters)". www.webforefront.com. Retrieved 2023-08-14.
  5. "Extensions". Jinja2 Documentation (2.8-dev). Retrieved 2015-05-26.
  6. DuPlain, R. (2013). Instant Flask Web Development. Packt Publishing. p. 30. ISBN 978-1-78216-963-5. Retrieved 2015-05-26.
  7. "Templating (Jinja2) — Ansible Documentation".
  8. "Understanding Jinja". docs.saltproject.io.
  9. Jinja and macros | dbt Developer Hub
  10. "Welcome | Jinja2 (The Python Template Engine)". palletsprojects.com/p/jinja.
  11. Ronacher, Armin. "Template Designer Documentation". Jinja2 Documentation. Retrieved 7 January 2016. A Jinja template doesn't need to have a specific extension: .html, .xml, or any other extension is just fine.
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