prefact 0.1.4

Automatic Python refactoring toolkit – detect, fix, and validate common code issues introduced by LLMs and humans alike.

prefact

Automatic Python refactoring toolkit — detect, fix, and validate common code issues introduced by LLMs and humans alike.

The Problem

When using LLMs for code generation, they often silently change import paths from absolute to deep relative:

# ❌ LLM introduces this
from ....llm.generator import generate_strategy
from ....loaders.yaml_loader import save_strategy_yaml

# ✅ You wanted this
from planfile.llm.generator import generate_strategy
from planfile.loaders.yaml_loader import save_strategy_yaml

prefact automatically detects, fixes, and validates such issues in a three-phase pipeline.

Features

Rule	ID	Auto-fix	Description
Relative → Absolute imports	relative-imports	✅	Converts from ....x import y to from pkg.x import y
Unused imports	unused-imports	✅	Removes imports never referenced in the module
Duplicate imports	duplicate-imports	✅	Removes the same name imported twice
Wildcard imports	wildcard-imports	🔍	Flags from x import *
Unsorted imports	sorted-imports	🔍	Flags import blocks not ordered stdlib→3rd-party→local
String concatenation	string-concat	🔍	Flags "Hello " + name → suggests f-strings
Print statements	print-statements	🔍	Flags debug print() calls
Missing return types	missing-return-type	🔍	Flags public functions without return type hints

✅ = auto-fix · 🔍 = scan-only (report)

Examples

The examples/ directory contains comprehensive examples for different use cases:

Example	Description
sample-project	Realistic project with all issues demonstrated
01-individual-rules	Each rule explained with before/after code
02-multiple-rules	Combining multiple rules for comprehensive cleanup
03-output-formats	Console vs JSON output examples
04-custom-rules	Writing your own refactoring rules
05-ci-cd	GitHub Actions, GitLab CI, Azure DevOps configs
06-api-usage	Using prefact programmatically from Python

Quick Example

# Try the sample project
cd examples/sample-project
prefact scan --path . --config prefact.yaml
prefact fix --path . --config prefact.yaml

See examples/README.md for a detailed guide to all examples.

Installation

pip install -e .

# with dev dependencies (pytest)
pip install -e ".[dev]"

Quick Start

# Generate config file
prefact init

# List all available rules
prefact rules

# Scan only (no changes)
prefact scan --path ./my_project --package mypackage

# Fix + validate (with backups)
prefact fix --path ./my_project --package mypackage

# Dry-run (show what would change)
prefact fix --path ./my_project --package mypackage --dry-run

# Check a single file
prefact check ./my_project/src/mypackage/core/service.py --package mypackage

# JSON output for CI
prefact fix --path . --format json -o report.json

📚 Want to see prefact in action? Check out our comprehensive examples with real-world scenarios!

Pipeline Architecture

┌─────────┐      ┌─────────┐      ┌────────────┐
│  SCAN   │ ──→  │   FIX   │ ──→  │  VALIDATE  │
│         │      │         │      │            │
│ Detect  │      │ Apply   │      │ Syntax OK? │
│ issues  │      │ fixes   │      │ Regressions│
│ per rule│      │ + backup│      │ preserved? │
└─────────┘      └─────────┘      └────────────┘

1. Scan — each rule walks the AST / CST and emits Issue objects
2. Fix — rules with auto-fix transform the source (via libcst for formatting-safe changes)
3. Validate — post-fix checks: syntax valid, no regressions, import counts preserved

Configuration

Create prefact.yaml (auto-generated via prefact init):

package_name: planfile

include:
  - "**/*.py"

exclude:
  - "**/venv/**"
  - "**/build/**"

rules:
  relative-imports:
    enabled: true
    severity: warning
  unused-imports:
    enabled: true
    severity: info
  duplicate-imports:
    enabled: true
  wildcard-imports:
    enabled: true
    severity: error
  sorted-imports:
    enabled: false
  string-concat:
    enabled: true
  print-statements:
    enabled: true
    options:
      ignore_patterns: ["cli.py", "scripts/"]
  missing-return-type:
    enabled: false

Python API

from pathlib import Path
from prefact.config import Config
from prefact.engine import RefactoringEngine

config = Config(
    project_root=Path("./my_project"),
    package_name="planfile",
    dry_run=False,
    backup=True,
)

engine = RefactoringEngine(config)
result = engine.run()

print(f"Found {result.total_issues} issues")
print(f"Fixed {result.total_fixed}")
print(f"All valid: {result.all_valid}")

Writing Custom Rules

Extend BaseRule and use the @register decorator:

from prefact.rules import BaseRule, register
from prefact.models import Issue, Fix, ValidationResult

@register
class MyCustomRule(BaseRule):
    rule_id = "my-custom-rule"
    description = "Does something useful."

    def scan_file(self, path, source):
        # Return list[Issue]
        ...

    def fix(self, path, source, issues):
        # Return (fixed_source, list[Fix])
        ...

    def validate(self, path, original, fixed):
        # Return ValidationResult
        ...

CI/CD Integration

# GitHub Actions
- name: prefact check
  run: |
    pip install ./prefact
    prefact scan --path . --format json -o prefact-report.json
    prefact fix --path . --dry-run

Running Tests

pip install -e ".[dev]"
pytest -v

License

Apache License 2.0 - see LICENSE for details.

Author

Created by Tom Sapletta - [e-mail]