zlib-py

A small pyo3 extension that exposes zlib-rs to Python. As a small proof of concept for the Rust for CPython effort.

Building

With Nix

nix build              # Python env with zlib_py importable, at ./result
nix run .#python -- -c 'import zlib_py; print(zlib_py.compress(...))'
nix develop            # cargo + rustc + maturin + the pinned python on PATH

The flake fetches CPython and pyo3 at the pinned revs (we'll attempt to keep this close to HEAD in both cases), then builds the extension with maturinBuildHook. The cargo registry is vendored in a fixed-output derivation so the actual build runs offline.

Without Nix

uv sync
uv run maturin develop
uv run python -c 'import zlib_py; print(zlib_py.compress(...))'

This uses whatever CPython + pyo3 your environment resolves (no guarantees of working).

Benchmarks

The benchmark script (vendored from farhaanaliii/zlib-rs-python) compares zlib_py against the stdlib zlib on the same interpreter. Run with:

./result-test/bin/python benchmarks/bench_zlib.py

Sample numbers from Darwin arm64 / CPython 3.16.0a0 (median of N iterations per upstream's schedule; sub-millisecond rows are noisy):

Operation	Size	CPython zlib	zlib_py	Speedup
decompress	1 MB (L6)	464 µs	91 µs	5.1× faster
decompress	10 MB (L6)	5.24 ms	868 µs	6.0× faster
stream compress	1 MB (L6)	1.52 ms	292 µs	5.2× faster
stream compress	10 MB (L6)	15.42 ms	2.77 ms	5.6× faster
stream decompress	1 MB (L6)	469 µs	127 µs	3.7× faster
compress	10 MB (L9)	14.82 ms	8.12 ms	1.8× faster
adler32	1 MB	273 µs	28 µs	9.7× faster
adler32	10 MB	2.77 ms	281 µs	9.9× faster
crc32	1 MB	34 µs	99 µs	2.9× slower
crc32	10 MB	343 µs	1.00 ms	2.9× slower
compress binary	1 MB (L6)	14.63 ms	12.03 ms	1.2× faster

crc32 regresses on payloads ≥64 KB because CPython's implementation uses Intel CRC32 intrinsics that zlib-rs 0.6.3 doesn't hit on aarch64-darwin.

Output bytes match stdlib exactly at level 9 and diverge at intermediate levels — engine-level property of zlib-rs, documented in THIRD_PARTY.md.

Rust for CPython — links

• Official GitHub org
• Pre-PEP discussion thread
• Latest progress update (2026-04)

Acknowledgements

Prior art and inspiration: farhaanaliii/zlib-rs-python a separate pyo3 binding to zlib-rs.

License

MIT