General Clean Code Principles

Critical Rules

G5: DRY (Don't Repeat Yourself)

Every piece of knowledge has one authoritative representation.

# Bad - duplication
tax_rate = 0.0825
ca_total = subtotal * 1.0825
ny_total = subtotal * 1.07

# Good - single source of truth
TAX_RATES = {"CA": 0.0825, "NY": 0.07}
def calculate_total(subtotal: float, state: str) -> float:
    return subtotal * (1 + TAX_RATES[state])