Code Refactoring Patterns

Apply safe refactoring with behavior preservation and test validation.

When to Use

• Improving code readability and maintainability
• Reducing duplication
• Preparing code for new features
• Addressing code review feedback

Core Refactoring Patterns

Extract Method

# Before
def process(data):
    # validate
    if not data: raise ValueError()
    if len(data) > 1000: raise ValueError("too large")
    # transform
    result = [item.strip().lower() for item in data]
    # save
    db.save(result)

# After
def process(data):
    validate(data)
    result = transform(data)
    save(result)

Replace Temp with Query

# Before
base = order.quantity * order.price
discount = base * 0.1 if order.is_bulk else 0
total = base - discount

# After
def base_price(order): return order.quantity * order.price
def discount(order): return base_price(order) * 0.1 if order.is_bulk else 0
def total(order): return base_price(order) - discount(order)

Introduce Parameter Object

# Before
def search(query, limit, offset, sort_by, sort_dir, filters):
    pass

# After
@dataclass
class SearchParams:
    query: str
    limit: int = 10
    offset: int = 0
    sort_by: str = "relevance"
    sort_dir: str = "desc"
    filters: dict = field(default_factory=dict)

def search(params: SearchParams):
    pass

Refactoring Safety Rules

Troubleshooting

Best Practices

Refactoring Safety Checklist

• [ ] All existing tests pass before starting
• [ ] Each refactoring step committed separately
• [ ] No behavior changes (same inputs → same outputs)
• [ ] All tests still pass after each step
• [ ] Complexity metrics improved
• [ ] PR is under 200 lines of changes

Related Skills

• fai-refactor-complexity — Reduce cyclomatic complexity
• fai-refactor-plan — Multi-sprint refactoring plans
• fai-code-smell-detector — Automated smell detection
• fai-review-and-refactor — Combined review + fix workflow