prylint

A Rust reimplementation of pylint's error checking that produces byte-for-byte identical output to pylint — 15–84× faster.

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 — verified byte-identically against real pylint on 27 production codebases (~105,000 messages across ~60,000 Python files), including django, numpy, pandas, sympy, home-assistant, sqlalchemy, twisted, 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

prylint targets pylint's errors-only mode. Use it exactly like pylint:

prylint . -E --disable=C0301,W0511,E0110,E0401,E0611,E1101,...

Output, message order, and exit codes match pylint . -E --disable=... (pylint 4.0.5).

Benchmarks

Measured against pylint 4.0.5 (single run, Apple M-series, 10 cores — prylint currently uses one core; parallel mode is in development):

Every row above is also an accuracy test: each repo's full output is byte-identical to pylint's.

How accuracy is verified

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 tables, brain transforms) across all corpus files: zero differences.
2. Inference fidelity — astroid's inference engine (the part that powers checks like not-callable and no-value-for-parameter) is ported exactly: lazy generator semantics, the 100-result cap, cache-eviction order, Uninferable propagation. Verified by dumping the inference result of every name/attribute/call node in every corpus file and comparing against astroid: byte-identical.
3. Output fidelity — full runs compared byte-for-byte, including message order, module headers, # pylint: pragma handling (disable/enable blocks, disable-next, skip-file), 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.

Determinism notes (where pylint disagrees with itself)

Two corners of pylint's output are nondeterministic between its own runs; prylint pins them:

• Crash reports (F0002) embed a wall-clock filename (pylint-crash-<timestamp>.txt). prylint emits the same message shape with its own timestamp.
• A few multi-message orderings iterate Python sets, so they depend on PYTHONHASHSEED. prylint reproduces CPython's iteration order for PYTHONHASHSEED=0 exactly (verified by fuzzing against the real interpreter), so it matches PYTHONHASHSEED=0 pylint … byte-for-byte.

Scope and limitations

• Errors-only mode: prylint implements pylint -E (all E/F checks except E0110, E0401, E0611, E1101) plus the message-control machinery (--disable, inline pragmas — including pragmas that re-enable messages locally). W/R/C checkers are not implemented except where inline pragmas in real code resurrect them.
• Pinned semantics: behavior matches pylint 4.0.5 / astroid 4.0.4 running on CPython 3.12. Newer Python syntax (3.13/3.14) is reported as a syntax error, exactly as that pylint would.
• Config files are not read: --rcfile is accepted but ignored; pyproject.toml/pylintrc discovery is not implemented yet. Pass options on the command line.
• Linted-code dependencies do not need to be installed (matching how the benchmark ground truth was produced). If your pylint runs with your project's full virtualenv on sys.path, set PRYLINT_PYTHON to that venv's interpreter for identical import resolution.

How it works

• File discovery, message control, and reporting are direct ports of pylint's own logic (down to os.walk ordering and the ************* Module header rules).
• 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…).
• 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.

The target invocation

prylint's accuracy contract is defined against this exact command:

pylint . -E --disable=C0301,W0511,C0114,R0402,C0116,R0914,W0718,R1735,W0105,R1705,W0603,W0104,C0209,W0719,C0411,C0412,R0912,R0915,C0413,C0115,C0103,W0613,R0801,W0602,R0913,R0917,W0622,R0902,R0911,R0913,R1702,R1716,W0212,R1728,C0121,R0916,C0415,W1401,C0206,C0302,R0904,W1514,R0903,E0110,R1714,W0707,R1718,W1309,W1203,E0611,W0611,W0108,W0177,E1101,C1803,R1721,W0123,R1720,R1710,W0221,W0122,C0201,W1510,R1729,R1737,C0325,R0401,E0401

Development

The differential-testing harness (corpus ground truth, AST/inference dump comparators, per-code diff triage) lives in harness/. The accuracy contract: any change must keep all 27 corpora byte-identical.

License

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