tholus

Astral's uv, the Rust Python package manager, compiled to WebAssembly.

Not affiliated with or endorsed by Astral. This is an independent port.

What it is

implement in three different places:

• Terminals: wire the engine to xterm.js and type uv pip install rich with real ANSI colors and live progress bars.
• Pyodide apps: a programmatic package-manager API for JupyterLite/PyScript/marimo-class hosts, with correct dependency resolution
• Tooling UIs: uv's PubGrub resolver as a library. Resolve, lock, and export without installing.

engine runs in a dedicated Web Worker. Embedding pages need no COOP/COEP headers and no SharedArrayBuffer.

Why not micropip

micropip has no real resolver. It takes the first satisfying version and raises on conflict, with no backtracking. uv brings PubGrub resolution, lockfiles, a persistent cache, and range-request metadata fetching.

Layout

Path	What lives there
vendor/uv/	Submodule: our fork of astral-sh/uv, one commit per seam patch
crates/uv-wasm-engine/	wasm-bindgen boundary, OPFS store, TTY and event plumbing
crates/uv-wasm-xtask/	Build pipeline: cargo then wasm-bindgen then wasm-opt
packages/	npm SDK (core, pyodide adapter, xterm addon, transports)
apps/demo/	demo site
test/parity/	parity tests against native uv
apps/testbed/	Playwright harness page
docs/	Architecture, spec, and integration guides

Documentation

Guide	What it covers
comparison.md	How this differs from micropip and Pyodide's loadPackage
embedding.md	Starting an engine, running commands, the typed pip/venv API
transports.md	platform, fetch and libcurl, and writing your own
pyodide.md	Mounting an environment into Pyodide, and PEP 517 build hooks
parity.md	How the byte-parity gate works and how to re-record fixtures
privacy.md	What leaves the browser, what is stored, what a host can turn off
hosting.md	Serving the artifact: brotli, immutable caching, CSP, and no COOP/COEP
architecture.md	How the pieces fit

Development

Requires bun >= 1.3 and the Rust toolchain pinned in rust-toolchain.toml.

bun install --linker=isolated
bun run build       # the packages, then the apps that bundle them
bun run test        # everything
cargo xtask build   # build the wasm engine artifact

bun run test splits into two projects: --project unit for everything that runs in-process, and --project browser for the seven files that launch Chromium, which run one at a time on purpose. Seven at once does not just run slowly. It produces failures that look like defects. See parity.md.

License

Apache-2.0 OR MIT. The vendored uv fork keeps upstream's licensing (uv-pep440 and uv-pep508 are Apache-2.0 OR BSD-2-Clause). No AGPL code is linked or shipped; see docs/transports.md.