@cowasm/cpython

WebAssembly version of Python built using Zig / Clang

Motivation

• Pyodide doesn't fully support using their build from node.js, whereas we do support it here.

• Using zig as a build system is faster than using pyodide + emscripten.

Build from source

This is part of a bigger package. Install the python-wasm github repo, then type make, and this will get built along the way.

The build is done entirely using Zig, so doesn't depend at all on having clang or gcc installed on your system. It works on MacOS and Linux, both aarch64 and x86_64. The resulting build contains:

• dist/native: a minimal native build of CPython which exists entirely to bootstrap the WebAssembly cross-compilation
• dist/wasm: a WASM build of CPython, which includes some .so shared libraries that are built -fPIC so they can be loader by a loader (see the dylink package). This also includes dist/wasm/lib/dist/python311.zip which is a minimal zip archive of pyc files, and currently also includes some .so files.

The Test Suite

If you run

make test

then the full CPython test suite for the WebAssembly build gets run properly. Currently a large number of tests do pass, but also there are many that fail. For example, in the Decimal module there's hundreds of tests that pass and exactly one that fails causing a full SEGFAULT.

The test suite runs on the server, "orchestrated" by our native build of cpython, and using node.js + our WASI and Posix support.

A major medium-term goal for this project is to get the entire test suite to pass.

Note that running make test at the top level of python-wasm does NOT run the large full cpython test suite yet, since there are numerous failures.

Issues

There are of course many, as documented in the GitHub issues: https://github.com/sagemathinc/cowasm-python/issues

How to use pip install from here

This assumes for now that you've downloaded the source code for python-wasm and are in the packages/cpython directory.

Build python-wasm, then run Python's ensurepip to install pip into python-wasm. You DO NOT need to build any other packages in the python-wasm repo -- each package works self contained!

make
make pip

Also make sure you have cowasm-cc, etc. in your path by doing this:

~$ pwd 
.../cowasm-python/packages/cpython
~$ cd ../..
~$ . bin/env.sh
~$ cd packages/cpython

Now you can use pip. Here's an example that involves grabbing a pure python package from pypi, and then finding that it depends on regexp

~$ ./bin/python-wasm -m pip parsimonious

The result is some new files in site-packages, which are compiled for WebAssembly:

~$ ls dist/wasm/lib/python3.11/site-packages/
README.txt                              pip-22.3.dist-info
_distutils_hack                         pkg_resources
distutils-precedence.pth                regex
parsimonious                            regex-2022.10.31-py3.11.egg-info
parsimonious-0.10.0.dist-info           setuptools
pip                                     setuptools-65.5.0.dist-info

~$ ls dist/wasm/lib/python3.11/site-packages/regex/*.so
dist/wasm/lib/python3.11/site-packages/regex/_regex.cpython-311-wasm32-wasi.so

You could then bundle them up somehow and include them wherever you want to use python-wasm... (TODO: better workflow and instructions to come in the future -- see https://github.com/sagemathinc/cowasm-python/issues/7).