Jinja2

Jinja2 is a modern templating language for Python designed to generate text by combining templates with data. Created by Armin Ronacher, it is a more feature-rich and Pythonic successor to Django’s template language. Jinja2 emphasizes speed, readability, and a flexible syntax, and it is widely used in web development and configuration tooling.

Key features include variable substitution, control structures, and a rich set of filters and tests for data transformation. It supports macros for reusable template fragments, template inheritance for composing layouts, and blocks to enable extensibility. Autoescaping for HTML and a sandboxed execution environment enhance security when rendering untrusted content. An extensible architecture allows additional functionality through extensions and custom filters or tests.

Template syntax uses double curly braces for expressions (for example, to output a value) and {% ... %} for statements such as loops and conditionals. Comments are written with {# ... #}. Filters can be chained, and templates can call user-defined macros or functions. Jinja2 compiles templates to Python code, which contributes to its performance.

Environment and loading mechanisms control how templates are found and rendered. Common loaders include FileSystemLoader for filesystem templates, PackageLoader for templates within packages, and DictLoader for in-memory templates. In practice, Jinja2 is the default templating engine for the Flask web framework and is also used by other tools such as Ansible and various configuration systems.

Jinja2 is distributed under a permissive BSD-style license and has a long-standing, active development community. It remains a popular choice for Python-based templating due to its balance of power, safety features, and ease of use.