fast-iso8601-rs

Rust-backed complete drop-in replacement for the frozen public and behavioral contract of iso8601==2.1.0. It keeps the iso8601 import namespace, call signatures, typing marker, datetime/timezone semantics and exception behavior. The native wheel moves the lexical parse and capture extraction into Rust; a universal pure-Python wheel supports Python 3.7 and platforms without a published native wheel.

import iso8601

value = iso8601.parse_date("2026-08-12T10:30:45.123456Z")
assert value.isoformat() == "2026-08-12T10:30:45.123456+00:00"
assert iso8601.is_iso8601("2026-08")

Install

The project is not published from this repository yet. After a release:

python -m pip install fast-iso8601-rs

Existing code continues to use import iso8601. Python 3.8+ selects a native wheel on supported platforms. Python 3.7 selects the py3-none-any fallback.

Compatibility and verification

The replacement is pinned to upstream 2.1.0, not an open-ended promise about future versions. See UPSTREAM-CONTRACT.md for the frozen surface and COMPATIBILITY.md for executable gates.

cargo fmt --all -- --check
cargo clippy --all-targets --all-features -- -D warnings
cargo test --all-targets
python -m pytest -q tests
PYTHON=python bash scripts/run_upstream_full.sh
python scripts/run_differential.py --oracle-python ORACLE --candidate-python CANDIDATE

Benchmark claims are accepted only for the exact installed wheel identified by filename and SHA256, with raw samples, median and p95 retained. No fixed speedup is claimed before that gate passes.

License

MIT. The frozen upstream notice and Rust dependency notices are retained in THIRD_PARTY_NOTICES.md.