Pywasm: A WebAssembly interpreter written in pure Python.

A WebAssembly interpreter written in pure Python, no third-party libraries are used.

The wasm version currently in use is: WebAssembly Specification, Release 2.0 (Draft 2025-04-25).

The wasi version currently in use is: WASI Preview 1.

Also requires Python version >= 3.12.

Installation

$ pip install pywasm

Some simple examples

1. First we need a wasm module! Grab our example/fibonacci/bin/fibonacci.wasm file and save a copy in a new directory on your local machine.

2. Now, instantiate WebAssembly modules directly from underlying sources. This is achieved using the Runtime.instance_from_file method.

import pywasm
pywasm.log.lvl = 1

runtime = pywasm.core.Runtime()
m = runtime.instance_from_file('example/fibonacci/bin/fibonacci.wasm')
r = runtime.invocate(m, 'fibonacci', [10])
print(f'fibonacci(10) = {r[0]}')

A brief description for example

File	Description
example/blake2b.py	Blake2b hashing algorithm
example/blake2b_direct.py	Make the hash result returned as a value, not as an output parameter
example/fibonacci.py	Fibonacci, which contains loop and recursion
example/fibonacci_env.py	Call python/native function in wasm
example/pi.py	Calculate π using the agm algorithm
example/wasi_httpbin.py	Execute a wasi program and http get from http://httpbin.org
example/wasi_ll.py	Execute a wasi program and list information about a directory
example/wasi_stdout.py	Execute a wasi program and capture stdout
example/wasi_zen.py	Execute a wasi program and print poem "The Zen of Python"

Test

$ python script/build_wabt.py # Download wabt tools at res/wabt.
$ python script/build_spec.py # Download spec tests at res/spec.
$ python script/build_wasi.py # Download wasi tests at res/wasi-testsuite.

$ python test/example.py      # Test example.
$ python test/spec.py         # Test spec.
$ python test/wasi.py         # Test wasi.

Performance

Pywasm is an interpreter implemented using pure python and its standard library, capable of running on any python platform. Due to the inherent characteristics of python, you should not have overly high expectations for pywasm's performance.

However, pywasm's design makes it jit-friendly. Compared to cpython, pywasm's performance on pypy can improve by approximately 10 times, significantly surpassing the average 3-fold improvement.

Thanks

• wagon
• warpy
• zstdpy

License

MIT