On: Pyodide 314.0: Python packages can now publish WebAssembly wheels to PyPI

[simonw]

I've been looking forward to this for ages!

This means we can now take any C/Rust/whatever extension for Python, compile that as a `.wasm` extension, and then load it directly in browser Pyodide projects using:

  await micropip.install("package-on-pypi")
  import package_name

Here's how to try the new feature out. Visit https://pyodide.org/en/stable/console.html and type:

  import micropip
  await micropip.install("pydantic_core")
  import pydantic_core

That gets you this WASM wheel: https://pypi.org/project/pydantic_core/#pydantic_core-2.47.0...

You can tell that it's got compiled code in (and not just Python) by running:

  pydantic_core._pydantic_core

I get this:

  <module 'pydantic_core._pydantic_core' from '/lib/python3.14/site-packages/pydantic_core/_pydantic_core.cpython-314-wasm32-emscripten.so'>

[simonw → simonw]

I had an older experimental Pyodide WASM project lying around (a packaging of the Luau language by Roblox) so I had Codex package that up for me and pushed it to PyPI.

Here's the package: https://pypi.org/project/luau-wasm/

  import micropip
  await micropip.install("luau-wasm")
  import luau_wasm
  print(luau_wasm.execute(r'''
  local animals = {"fox", "owl", "frog", "rabbit"}
  table.sort(animals, function(a, b) return #a < #b end)
  for i, name in animals do print(i .. ". " .. name .. " (" .. #name .. ")") end
  '''))

And an interactive demo page where you can try it out: https://simonw.github.io/luau-wasm/

Wrote about this in more detail on my blog: https://simonwillison.net/2026/Jun/13/publishing-wasm-wheels...

[westurner → simonw]

Here are all of the existing emscripten-forge recipes for building WASM packages: https://github.com/emscripten-forge/recipes/tree/main/recipe...

From https://news.ycombinator.com/item?id=43201706 :

> jupyterlite-xeus supports environment.yml with jupyterlite with packages from emscripten-forge: https://jupyterlite-xeus.readthedocs.io/en/latest/environmen...

emscripten-forge was a Quetz repo built with but is now hosted on prefix.dev.

From https://emscripten-forge.org/blog/ :

  pixi run setup

  pixi run build-emscripten-wasm32-pkg recipes/recipes_emscripten/regex

Pixi doesn't yet support building wheels though, just conda recipes.

Does cibuildwheel already have this new support for building WASM pyodide packages?

Does jupyterlite's `micropip install` install these new WASM packages from PyPI?

[rtpg → simonw]

Is there any form of client-side caching that kicks in with all of this flow?

Tbh I don't feel great about people just writing up a bunch of scripts pulling things just on every run.

[simonw → rtpg]

Browser caching works with stuff pulled from PyPI, so it shouldn't get loaded more than once.