Jinja (template engine)
| File:Jinja software logo.svg | |
| Original author(s) | Armin Ronacher |
|---|---|
| Initial release | July 17, 2008[1] |
| Written in | Python |
| Type | Template engine |
| License | BSD License |
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. The Jinja template engine allows customization of tags,[2] filters (for formatting or transforming values[3]), tests (for evaluating conditions[3]), and globals.[4] 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 [5] and it is also used by Ansible,[6] Trac, and Salt.[7] It is also used to make SQL macros, for example for use with dbt.[8]
Features
Some of the features of Jinja are:[9]
- 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 a number sign (#) 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 }}).[3]
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 %}).[3]
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:[10]
<!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 <unsafe> data</title>
</head>
<body>
1,
2,
3,
4,
5,
6
</body>
</html>
Note the minus sign (-) after the tag {%: If you add a minus sign (-) to the start or end of a block (e.g. a For tag), a comment, or a variable expression, the whitespaces before or after that block will be removed.[11]
References
- ↑ "Jinja2 Release History". Retrieved 24 June 2020.
- ↑ "Extensions". Jinja2 Documentation (2.8-dev). Retrieved 2015-05-26.
- ↑ 3.0 3.1 3.2 3.3 "Jinja built-in filters and tests (like Django filters)". www.webforefront.com. Retrieved 2023-08-14.
- ↑ "Extensions". Jinja2 Documentation (2.8-dev). Retrieved 2015-05-26.
- ↑ DuPlain, R. (2013). Instant Flask Web Development. Packt Publishing. p. 30. ISBN 978-1-78216-963-5. Retrieved 2015-05-26.
- ↑ "Templating (Jinja2) — Ansible Documentation".
- ↑ "Understanding Jinja". docs.saltproject.io.
- ↑ Jinja and macros | dbt Developer Hub
- ↑ "Welcome | Jinja2 (The Python Template Engine)". palletsprojects.com/p/jinja.
- ↑ Ronacher, Armin. "Template Designer Documentation". Jinja Documentation (3.0.x). Retrieved 9 January 2024.
A Jinja template doesn't need to have a specific extension: .html, .xml, or any other extension is just fine.
- ↑ "Template Designer Documentation — Jinja Documentation (3.0.x)". jinja.palletsprojects.com. Retrieved 2024-01-09.