Rejig

Comprehensive Python code refactoring, analysis, and transformation.

Rejig provides a fluent API for finding and modifying Python code elements. Whether you're building codemods, automating refactoring, analyzing code quality, or managing large-scale migrations, Rejig gives you precise control over your codebase.

Features

Code Manipulation

• Target-based API — Everything is a target: files, modules, classes, functions, methods, lines
• Fluent chaining — rj.file("app.py").find_class("User").find_method("save")
• Batch operations — Apply changes to multiple targets with TargetList
• Atomic transactions — Collect changes and apply atomically with rollback
• Patch support — Parse, generate, apply, and reverse unified/git diffs
• Safe by default — Operations return Result objects, never raise exceptions
• Dry-run mode — Preview all changes before applying

Code Analysis

• Complexity analysis — Cyclomatic complexity, nesting depth, function length
• Dead code detection — Unused functions, classes, variables, imports
• Pattern detection — Missing type hints, bare excepts, magic numbers
• Security scanning — Hardcoded secrets, injection vulnerabilities, unsafe operations
• Optimization detection — Duplicate code, loop improvements

Code Transformation

• Import management — Organize, detect unused, fix circular imports
• Type hints — Infer, modernize, and generate type annotations
• Docstrings — Generate and update in Google, NumPy, or Sphinx style
• Code generation — Dunder methods, properties, test stubs
• Modernization — f-strings, Python 3.10+ syntax, deprecated API replacement

Project Management

• pyproject.toml — Manage metadata, dependencies, scripts
• Tool configuration — Black, Ruff, mypy, pytest, isort, coverage
• Package format conversion — requirements.txt, Poetry, PEP 621, UV

Framework Support

• Django — Settings, URLs, app discovery
• Flask — Routes, blueprints, error handlers
• FastAPI — Endpoints, dependencies, middleware
• SQLAlchemy — Models, relationships

Quick Example

from rejig import Rejig

rj = Rejig("src/")

# Find all test classes and add a decorator
rj.find_classes(pattern="^Test").add_decorator("pytest.mark.slow")

# Rename a method and update all references
rj.file("models.py").find_class("User").find_method("get_name").rename("get_full_name")

# Add type hints to all functions
rj.find_functions().infer_type_hints()

# Generate docstrings for functions without them
rj.find_functions().without_docstrings().generate_docstrings(style="google")

# Find security issues
security_issues = rj.find_security_issues()
print(f"Found {len(security_issues)} security issues")

# Modify pyproject.toml
rj.toml("pyproject.toml").set("tool.black.line-length", 110)

Why Rejig?

Task	Without Rejig	With Rejig
Rename a method	Find/replace (breaks things)	target.rename("new_name")
Add decorator to many classes	Manual editing	targets.add_decorator("@cached")
Find security vulnerabilities	External tools, CI setup	rj.find_security_issues()
Add type hints to legacy code	Manual annotation	rj.find_functions().infer_type_hints()
Generate docstrings	Write each one	targets.generate_docstrings()
Update pyproject.toml	Parse, modify, serialize	rj.toml(path).set(key, value)
Find duplicate code	Manual review	DRYAnalyzer(rj).find_all_issues()

Installation

pip install rejig

# With framework support
pip install rejig[django]
pip install rejig[all]

Documentation

Getting Started

• Installation — Install and verify
• Quickstart — Get up and running in 5 minutes
• Core Concepts — Understand targets, results, and the API design

Guides

Finding & Modifying Code

• Finding Code — Locate classes, functions, methods, and more
• Modifying Code — Rename, add, remove, and transform code
• Batch Operations — Work with multiple targets
• Line Operations — Work with individual lines and ranges

Code Quality

• Code Analysis — Complexity, dead code, patterns
• Security Analysis — Find vulnerabilities and secrets
• Code Optimization — Detect duplicates and improvements

Code Transformation

• Import Management — Organize and manage imports
• Type Hints — Infer, modernize, and add type annotations
• Docstrings — Generate and update documentation
• Code Generation — Generate boilerplate code

Configuration

• Config Files — TOML, YAML, JSON, INI manipulation
• Project Management — pyproject.toml and dependencies
• Transactions — Atomic operations with rollback
• Patching — Parse, generate, apply, and reverse patches

Framework-Specific

• Django — Django project operations
• Flask — Flask application refactoring
• FastAPI — FastAPI endpoint management

Error Handling

• Error Handling — Result-based error handling patterns

Examples & Recipes

• Refactoring Patterns — Common refactoring scenarios
• Codemod Recipes — Ready-to-use migration scripts
• Optimization Recipes — Code quality improvements
• Analysis Recipes — Code analysis scripts
• Security Recipes — Security scanning scripts

API Reference

• Rejig Class — Main entry point
• Targets — All target classes
• Results — Result classes
• Patching — Patch parsing, generation, and targets
• Analysis — Analysis types and findings
• Security — Security types and findings

Sample Projects

• Sample Projects — Test projects for trying recipes