Jinja is a fast, expressive, extensible templating engine. Special placeholders in the template allow writing code similar to Python syntax. Then the template is passed data to render the final document.

It includes:

Template inheritance and inclusion.
Define and import macros within templates.
HTML templates can use autoescaping to prevent XSS from untrusted user input.
A sandboxed environment can safely render untrusted templates.
AsyncIO support for generating templates and calling async functions.
I18N support with Babel.
Templates are compiled to optimized Python code just-in-time and cached, or can be compiled ahead-of-time.
Exceptions point to the correct line in templates to make debugging easier.
Extensible filters, tests, functions, and even syntax.

Jinja's philosophy is that while application logic belongs in Python if possible, it shouldn't make the template designer's job difficult by restricting functionality too much.