pywasm3

Python bindings for Wasm3, a fast WebAssembly interpreter and the most universal WASM runtime.

Main repository: Wasm3 project

Requires CPython 3.11+. Wheels are cp311-abi3, so one wheel per platform covers 3.11 and newer.

Install

pip install pywasm3
pip install "pywasm3 @ git+https://github.com/wasm3/pywasm3"   # bleeding edge
pip install .                                                  # local copy

With uv:

uv add pywasm3
uv add "pywasm3 @ git+https://github.com/wasm3/pywasm3"        # bleeding edge
uv run --with pywasm3 python my_script.py                      # without a project

Usage example

import wasm3

WAT = """
(module
  (func $fib (export "fib") (param $n i64) (result i64)
    (if (i64.lt_u (local.get $n) (i64.const 2))
      (then (return (local.get $n))))
    (return (i64.add (call $fib (i64.sub (local.get $n) (i64.const 2)))
                     (call $fib (i64.sub (local.get $n) (i64.const 1))))))
)
"""

env = wasm3.Environment()
rt  = env.new_runtime(2048)
mod = env.parse_module(WAT)          # or a binary module, as bytes
rt.load(mod)
wasm_fib = rt.find_function("fib")
result = wasm_fib(24)
print(result)                       # 46368

Examples

Every script in examples/ carries its dependencies inline (PEP 723), so uv run sets up an environment for it on the fly — nothing to install first:

uv run examples/00-fibonacci.py     # wasm3 vs. pure Python fib(24)
uv run examples/01-coremark.py      # CoreMark benchmark
uv run examples/02-metered.py       # gas metering
uv run examples/03-asyncified.py    # asyncified module driven by asyncio
uv run examples/04-suspend-resume.py # pause, snapshot, Ctrl+C, resume in a new process
uv run examples/pygame-doomfire.py  # one of the pygame demos

The scripts resolve pywasm3 from this checkout, so they build the extension you have locally. Add --no-sources to run them against the released package instead:

uv run --no-sources examples/00-fibonacci.py

Documentation

• Text format - the bundled wat2wasm / wasm2wat
• Suspend, resume and snapshots - pause a call, save it, pick it up in another process
• Exceptions - Wasm exceptions in and out of the guest, and Python ones through it
• Development - building from source, tests, releases

License

This project is released under The MIT License (MIT)