Fable Converted Pylint to Rust

A Rust reimplementation of pylint that produces byte-for-byte identical output — 15–2300× faster (median ~85×).

prylint is not "inspired by" pylint. It is a bug-for-bug port: the same messages, at the same lines and columns, with the same text, in the same order, with the same exit codes and the same Your code has been rated footer — verified byte-identically against real pylint on 52 production codebases (~65,000 Python files), including django, numpy, pandas, sympy, home-assistant, sqlalchemy, twisted, scikit-learn, and pylint's own functional test suite. Where pylint has bugs, prylint reproduces them. Where pylint crashes, prylint reports the same crash message.

Install

pip install prylint

Requirements: a python3 (≥3.9) on PATH (used only to mirror pylint's module-resolution paths and to reproduce CPython's exact syntax-error messages for unparseable files). pylint and astroid themselves are not required.

Usage

Use it exactly like pylint — full check mode is the default:

prylint .                      # all checks (like `pylint .`)
prylint -E .                   # errors only (like `pylint -E .`)
prylint --disable=C0114,... .  # same --disable / --enable / inline pragmas

Output, message order, exit codes, the score footer, --rcfile / pyproject.toml discovery, init-hook, and # pylint: pragmas all match pylint 4.0.5.

Benchmarks

prylint . vs pylint . (both full check mode), pylint 4.0.5, Apple M-series, single-threaded:

(These 27 are the large repos that are slow enough to time meaningfully; the full accuracy suite is 52 repos — see below.)

Median per-repo speedup ~85×; the aggregate is higher because pylint's duplicate-code check (R0801) is O(n²) and dominates on test-heavy repos like black. These are single-core numbers — the inference engine is single-threaded to replicate astroid's order-sensitive global cache exactly (see LIMITATIONS.md), and that byte-identical path is already 15–2300× pylint.

Every row above is also an accuracy test: each repo's full output is byte-identical to pylint's (see exceptions in LIMITATIONS.md).

Accuracy

prylint was built by differential testing against pinned pylint 4.0.5 / astroid 4.0.4 / CPython 3.12:

1. AST fidelity — prylint's parse tree (built on the ruff parser) is compared node-by-node against astroid's (positions, scopes, locals, brain transforms) across all corpus files: zero differences.
2. Inference fidelity — astroid's inference engine is ported exactly: lazy-generator semantics, the 100-node inference budget, the bounded-LRU caches (lookup 128, _metaclass_lookup_attribute 1024) with their exact eviction, the 64-entry inference-tip FIFO, Uninferable propagation. Every name/attribute/call node's inference is dumped and compared against astroid.
3. Output fidelity — full runs compared byte-for-byte, including message order, module headers, the score footer, # pylint: pragma handling (disable/enable blocks, disable-next, skip-file), config-file discovery, and exit-code bitmasks.
4. Blind testing — two batteries of 10 repos each were added after development and judged cold; every divergence was root-caused and fixed.

Known, documented exceptions (one obscure SQLAlchemy class; the deliberately excluded no-member family; the places pylint is nondeterministic against itself) are catalogued in LIMITATIONS.md.

How it works

• File discovery, message control, config parsing, and reporting are direct ports of pylint's own logic (down to os.walk ordering, the ************* Module header rule, and the score-report footer).
• Parsing uses ruff's Rust parser, then rebuilds astroid's exact tree shape (docstring extraction, decorator positions, implicit class locals, metaclass handling, brain transforms for dataclasses/enums/namedtuples/attrs/…).
• A full port of astroid's inference engine resolves names, calls, attributes, MROs, and operator protocols with astroid's exact conservatism — including its caches and their quirks, because the quirks are observable in the output.
• Files the Rust parser rejects are re-judged by CPython itself (an embedded, stdlib-only helper) so syntax-error messages match ast.parse exactly.

Reproducing the test suite

scripts/setup_corpora.sh clones all 52 corpora at pinned commits and builds the pinned pylint/astroid ground-truth venv. The accuracy contract: every change must keep the corpora byte-identical (harness/ holds the differential comparators).

License

GPL-2.0-or-later, the same license as pylint — prylint reproduces pylint's message texts and behavior verbatim.