A WebAssembly interpreter written in pure Python
WebAssembly
518
181 commits
updated Sep 18, 2026
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.
$ pip install pywasm
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" |
$ 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.
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.
334 followers · starred Aug 2023
7,255 followers · starred Jun 2026
289 followers · starred Oct 2022
293 followers · starred Jul 2019
A WebAssembly interpreter written in pure Python
WebAssembly
518
181 commits
updated Sep 18, 2026
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.
$ pip install pywasm
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" |
$ 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.
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.
334 followers · starred Aug 2023
7,255 followers · starred Jun 2026
289 followers · starred Oct 2022
293 followers · starred Jul 2019