jinja

Project Overview

Jinja is a fast, expressive, and extensible Python templating engine. Templates use special placeholders with Python-like syntax, and data is passed in to render the final document. It is widely used for web pages and general text generation, with autoescaping, sandboxing, template inheritance, and i18n built in. Templates are compiled to optimized Python code just-in-time and cached for excellent performance.

Application logic stays in Python while template designers keep full freedom.

Key Features

• Template inheritance: reuse layouts with extends and block, plus includes
• Macros: define and import macros within templates for reusable fragments
• Autoescaping: HTML templates escape untrusted input automatically to prevent XSS
• Sandboxing: a sandboxed environment renders untrusted templates safely
• Async support: AsyncIO support for generating templates and calling async functions
• Internationalization: I18N support with Babel
• JIT compilation: templates compile to optimized Python code and get cached
• Extensible: filters, tests, functions, and even syntax are customizable
• Debuggable: exceptions point to the correct template line

Target Audience

• Flask and Python web developers
• Backend engineers generating HTML emails and reports
• Static site and documentation tool builders
• Developers needing code-generation templates

Quick Start

1. Install: pip install jinja2
2. Load and render a template from code

from jinja2 import Template

tpl = Template('Hello, {{ name }}!')
print(tpl.render(name='Jinja'))

3. In web apps, use inheritance and blocks across template files

{% extends 'base.html' %}
{% block content %}
  <ul>
  {% for user in users %}
    <li><a href='{{ user.url }}'>{{ user.username }}</a></li>
  {% endfor %}
  </ul>
{% endblock %}

Core Advantages

• Great performance: just-in-time compilation and caching keep rendering cheap
• Secure defaults: autoescaping and sandboxing lower injection risks
• Expressive: control structures, filters, and macros out of the box
• Wide adoption: the template engine behind Flask, Pelican, Ansible, and more

System Requirements

Notes

• Manual construction escapes nothing: rendering via the Template class does not autoescape, use an autoescape-enabled Environment for web output
• Keep logic out of templates: put complex business logic in Python and let templates focus on display