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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=...) in the class body. ClassVar assignments are ignored because they are not dataclass fields, and annotated assignments inside method bodies are ignored because they are locals.

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.

CodSpeed runs parser-and-rule benchmarks for representative modules on every pull request and every push to main, providing stable comparisons against the default-branch baseline. The scheduled Typeshed benchmark remains as a real-project correctness and gross-regression check.

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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