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

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.
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/blake2b_iter.py	A benchmarking example using the blake2b hash function
example/blake2b_simd.py	Use SIMD instructions to accelerate the blake2b hash function
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/main.py         # Test main.
$ 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

License

MIT

Release files for pywasm 2.2.3

For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.

Source distribution (sdist)

Source distribution for pywasm 2.2.3
File	Size	Uploaded
pywasm-2.2.3.tar.gz	631.9 kB	May 13, 2026	Details

Built distribution (wheel)

Table of built distributions (wheels) for pywasm 2.2.3
File	Interpreter	ABI	Platform	Reset
pywasm-2.2.3-py2.py3-none-any.whl 44.6 kB May 13, 2026	Python 3, Python 2	none	any	Details

Total release size: 676.5 kB

Release files / pywasm-2.2.3.tar.gz

Download URL	pywasm-2.2.3.tar.gz
Size	631.9 kB
Tags	Source
SHA-256 checksum How to use checksums	`bc5c2aaed73d43fdfab0c6c6dc3a05b4c2de176fbbf94dd258f4f26d135f0ff1`
BLAKE2b-256 checksum How to use checksums	`2051337c1ebcf5a534153c1d65e90bc0bcbfb3713b6f398d790b6ef4beede7f8`
Upload date	May 13, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`twine/6.2.0 CPython/3.14.4`

Release files / pywasm-2.2.3-py2.py3-none-any.whl

Download URL	pywasm-2.2.3-py2.py3-none-any.whl
Size	44.6 kB
Tags	Python 2 Python 3
SHA-256 checksum How to use checksums	`5bc0d4fa7a4404937b1f0fa7ca4622a70ddbef0491869f5aef7b2a1018f37aa0`
BLAKE2b-256 checksum How to use checksums	`73637a6587416281ddcd987b2a19e79406c9ba13b63fd5c7ae34ae35a06f89b1`
Upload date	May 13, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`twine/6.2.0 CPython/3.14.4`