chameleon-rs

A Rust implementation of the Chameleon page template engine, compatible with Chameleon's syntax and API.

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llms.txt
llms-full.txt

Developers

Michael Kennedy

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Requires: Python >=3.12

chameleon-rs is a Rust implementation of the Chameleon page template engine for Python. It aims to be a drop-in replacement: the same template language, the same Python API, byte-identical output, and much faster rendering.

from chameleon_rs import PageTemplate

page = PageTemplate('<p tal:repeat="name names">Hello, ${name}!</p>')
print(page(names=['World', 'Rust']))
<p>Hello, World!</p>
<p>Hello, Rust!</p>

Why chameleon-rs

  • Drop-in. Chameleon’s own test suite passes unmodified, and two production Flask/Quart sites render byte-identical HTML on every page. An existing app switches with one line at startup, and nothing else changes.
  • Fast. Rendering is about 4x to 7x faster than Chameleon on synthetic pages, and about 2.2x faster across real application pages, where the app’s own Python code takes most of the time. Templates compile about 70x faster, so the first request after a deploy or reload is quick too.
  • Partials built in. Every template can call ${render_partial('shared/card.pt', item=item)}. The partial renders natively inside the page, about 10x faster than Chameleon with chameleon_partials.
  • Flask and Quart built in. chameleon_rs.flask has chameleon-flask’s API.
  • No runtime dependencies. The package uses only the standard library. Stock Chameleon doesn’t need to be installed.

Install

uv pip install chameleon-rs

chameleon-rs needs Python 3.12 or later. The wheels include the compiled engine, so you don’t need a Rust toolchain.

Switch an existing app

Put this at the very top of your app’s entry point, before anything imports Chameleon:

import chameleon_rs.compat

chameleon_rs.compat.install()

From then on, import chameleon, import chameleon_partials and import chameleon_flask all give you chameleon-rs. See Switching from Chameleon.

Where to next

  • Getting started: render a first template and set up a template folder.
  • Language reference: TAL, METAL, i18n and ${...}, the language you already know from Chameleon.
  • Compatibility: what’s identical, the few known differences, and how compatibility is measured.
  • Performance: the benchmarks and how to reproduce them.