python

Critical Patterns

Type Hints (REQUIRED)

# ✅ ALWAYS: Use type hints for all function signatures
def calculate_total(items: list[dict], tax_rate: float = 0.1) -> float:
    """Calculate total with tax."""
    subtotal = sum(item["price"] for item in items)
    return subtotal * (1 + tax_rate)

# ❌ NEVER: Untyped functions
def calculate_total(items, tax_rate=0.1):
    return sum(i["price"] for i in items) * (1 + tax_rate)

Docstrings (REQUIRED)