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no-defaults

A fast, standalone Python linter that forbids defaults in function signatures and dataclasses. It is implemented in Rust and parses Python with Ruff's parser.

from dataclasses import dataclass, field

def connect(timeout=30):  # NOD001
    pass

@dataclass
class Job:
    retries: int = 3  # NOD001
    tags: list[str] = field(default_factory=list)  # NOD001

Installation

uv tool install no-defaults

Usage

no-defaults .
no-defaults --fix .
no-defaults --diff .
no-defaults --private-only src tests
no-defaults --output-format json .
no-defaults --output-format github .
no-defaults --show-settings src/package/api.py

Exit status is 0 when clean, 1 when violations are found, and 2 for an operational error. Directories are walked in parallel, respecting .gitignore and standard hidden-file filters. Diagnostics use Ruff's concise format and include a summary:

src/example.py:4:17: NOD001 parameter `timeout` of function `connect` has a default
Found 1 error.

Pass --fix to remove defaults automatically. Function parameters and ordinary dataclass assignments become required. For field(...), only the positional default, default=, or default_factory= argument is removed; other metadata is preserved:

retries: int = field(default=3, kw_only=True)
# becomes
retries: int = field(kw_only=True)

After a successful fix, the command exits with status 0 and prints a Ruff-style summary such as Found 2 errors (2 fixed, 0 remaining). Writes use an atomic same-directory replacement. --diff prints a unified diff, writes nothing, and exits with status 1 when changes are available.

The default full output includes source excerpts and carets. concise emits one diagnostic per line, json emits a machine-readable array, and github emits workflow commands for GitHub Actions annotations.

The linter detects defaults on positional-only, positional-or-keyword, and keyword-only parameters. For classes decorated with @dataclass or @dataclasses.dataclass, it detects assigned defaults plus field(default=...) and field(default_factory=...). ClassVar assignments are ignored because they are not dataclass fields.

Suppress an individual violation with either a blanket # noqa or the rule-specific # noqa: NOD001 on the line containing the default:

def compatible(timeout=30):  # noqa: NOD001
    pass

Suppress the rule for an entire file with # ruff: noqa or # ruff: noqa: NOD001.

Configuration

Configuration lives in pyproject.toml:

[tool.no_defaults]
private_only = true

[tool.no_defaults.per_file_enforcement]
"tests/**" = "all"
"src/**" = "private"

Private means a name that starts with one underscore. In private-only mode, the rule applies to private modules and packages, private functions and methods, all members of private classes, and private dataclass fields. For example, all defaults in _module.py and _package/module.py are checked. Dunder names such as __init__.py are not considered private by themselves.

per_file_enforcement accepts Ruff-style glob patterns relative to the directory containing pyproject.toml. Use "all" to reject every default in matching files or "private" to reject defaults only in private scopes. Patterns without a slash match file names at any depth. An initial ! negates a pattern. If multiple patterns match, the most specific pattern wins; equally specific patterns are resolved lexicographically so results never depend on TOML table order.

The --private-only CLI flag overrides the configuration for every checked file.

Like Ruff, no-defaults discovers the closest pyproject.toml containing [tool.no_defaults] separately for each file. This supports monorepos with nested configuration; files without a local table continue searching parent directories.

Performance

An optimized 1.0.0 development build checked a pinned Typeshed checkout containing 5,368 Python and stub files (12.5 MiB) in a median 0.29 seconds across five warm runs on an Apple Silicon Mac, or roughly 18,000 files per second. It produced 50,974 diagnostics; an earlier full-output measurement used approximately 41 MiB maximum RSS.

The scheduled Typeshed benchmark workflow repeats this against a pinned upstream revision and fails on parser errors, unexpected results, or a gross performance regression.

pre-commit

repos:
  - repo: https://github.com/adamtheturtle/no-defaults
    rev: v1.0.0
    hooks:
      - id: no-defaults

License

MIT

See CONTRIBUTING.md, SECURITY.md, and CHANGELOG.md.

Project links

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  • Released:
Newer release available (1.1.0)

1 maintainer

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Avatar for adamtheturtle from gravatar.com adamtheturtle

Credits

Author: Adam Dangoor

GitHub Statistics

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The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License expression

MIT
View SPDX License List

Requires

Python >=3.9

Tags

lint defaults dataclasses pre-commit

Classifiers

Report project as malware

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