Reduce Code Complexity

Identify and reduce complexity with extraction, simplification, and testing.

When to Use

• Functions with cyclomatic complexity > 10
• Deeply nested conditionals (> 3 levels)
• Long methods (> 50 lines)
• Code that's hard to test due to branching

Measure Complexity

# Python: radon
pip install radon
radon cc src/ -a -nb  # Show average, skip low complexity

# JavaScript: complexity-report
npx complexity-report --format json src/

# .NET: dotnet-sonarscanner (or build-in VS metrics)

Reduction Techniques

1. Extract Method

# Before: complexity 8
def process_order(order):
    if not order.items:
        raise ValueError("Empty order")
    if not order.customer:
        raise ValueError("No customer")
    subtotal = sum(i.price * i.qty for i in order.items)
    tax = subtotal * 0.08
    total = subtotal + tax
    if order.customer.is_vip:
        total *= 0.9
    order.total = total
    db.save(order)
    notify(order)
    return total

# After: complexity 3 (main) + 2 + 2 = lower per-function
def process_order(order):
    validate(order)
    total = calculate_total(order)
    finalize(order, total)
    return total

def validate(order):
    if not order.items: raise ValueError("Empty")
    if not order.customer: raise ValueError("No customer")

def calculate_total(order):
    subtotal = sum(i.price * i.qty for i in order.items)
    total = subtotal * 1.08
    return total * 0.9 if order.customer.is_vip else total

2. Early Returns (Guard Clauses)

# Before: nested
def get_discount(user, order):
    if user:
        if user.is_vip:
            if order.total > 100:
                return 0.2
            else:
                return 0.1
        else:
            return 0
    return 0

# After: flat
def get_discount(user, order):
    if not user or not user.is_vip:
        return 0
    return 0.2 if order.total > 100 else 0.1

3. Replace Conditional with Polymorphism

# Before
def calculate_price(product):
    if product.type == "subscription":
        return product.monthly * 12 * 0.8
    elif product.type == "one_time":
        return product.price
    elif product.type == "usage":
        return product.units * product.rate

# After
class Subscription:
    def price(self): return self.monthly * 12 * 0.8
class OneTime:
    def price(self): return self._price
class Usage:
    def price(self): return self.units * self.rate

Complexity Targets

Troubleshooting