Advanced Code Example — Classes and OOP#

# ══════════════════════════════════════════════════════════
#  BASE CLASS — Standard Customer
# ══════════════════════════════════════════════════════════
class Customer:
    """Represents a standard retail customer."""

    tier_thresholds = {
        'Platinum': 1000,
        'Gold': 500,
        'Silver': 200
    }

    def __init__(self, name: str, customer_id: int, region: str):
        self.name = name
        self.customer_id = customer_id
        self.region = region
        self.purchases = []
        self.account_type = 'Standard'

    def add_purchase(self, amount: float) -> None:
        if amount <= 0:
            raise ValueError(f"Purchase amount must be positive, got {amount}")
        self.purchases.append(round(amount, 2))

    def total_spent(self) -> float:
        return round(sum(self.purchases), 2)

    def purchase_count(self) -> int:
        return len(self.purchases)

    def average_purchase(self) -> float:
        if not self.purchases:
            return 0.0
        return round(self.total_spent() / self.purchase_count(), 2)

    def classify_tier(self) -> str:
        total = self.total_spent()
        for tier_name, threshold in self.tier_thresholds.items():
            if total >= threshold:
                return tier_name
        return 'Standard'

    def shipping_discount(self) -> float:
        tier_discounts = {'Platinum': 0.15, 'Gold': 0.10, 'Silver': 0.05, 'Standard': 0.00}
        return tier_discounts.get(self.classify_tier(), 0.00)

    def summary(self) -> str:
        return (f"[{self.account_type}] {self.name} (ID: {self.customer_id}) | "
                f"Region: {self.region} | Total: ${self.total_spent():,.2f} | "
                f"Tier: {self.classify_tier()} | Discount: {self.shipping_discount()*100:.0f}%")

    def __repr__(self) -> str:
        return f"Customer(name='{self.name}', id={self.customer_id})"


# ══════════════════════════════════════════════════════════
#  SUBCLASS — Premium Customer (inherits from Customer)
# ══════════════════════════════════════════════════════════
class PremiumCustomer(Customer):
    """Premium member with enhanced benefits and dedicated support."""

    def __init__(self, name: str, customer_id: int, region: str, membership_years: int):
        super().__init__(name, customer_id, region)  # call parent __init__
        self.membership_years = membership_years
        self.account_type = 'Premium'

    def loyalty_bonus(self) -> float:
        """Additional discount based on membership longevity."""
        if self.membership_years >= 5:
            return 0.05
        elif self.membership_years >= 2:
            return 0.03
        return 0.01

    def shipping_discount(self) -> float:
        """Override parent: premium gets base + loyalty bonus."""
        base = super().shipping_discount()
        return min(base + self.loyalty_bonus(), 0.30)  # capped at 30%

    def summary(self) -> str:
        base = super().summary()
        return f"{base} | Loyalty Bonus: {self.loyalty_bonus()*100:.0f}% | Member: {self.membership_years}yr"


# ══════════════════════════════════════════════════════════
#  PORTFOLIO — Mixed customer types, shared interface
# ══════════════════════════════════════════════════════════
portfolio: list[Customer] = [
    Customer('Bob Martinez', 1002, 'Southwest'),
    Customer('David Kim', 1004, 'Southeast'),
    PremiumCustomer('Alice Johnson', 1001, 'Northwest', membership_years=6),
    PremiumCustomer('Carol Chen', 1003, 'Northwest', membership_years=3),
]

# Add purchases
purchases_data = {
    'Alice Johnson': [250.50, 180.75, 420.25, 310.00, 420.00, 380.00],
    'Bob Martinez':  [95.80, 215.25, 110.00],
    'Carol Chen':    [300.00, 290.75, 300.00, 410.00],
    'David Kim':     [45.00, 60.00],
}

for customer in portfolio:
    for amount in purchases_data.get(customer.name, []):
        customer.add_purchase(amount)

# Print summaries — same .summary() call works for BOTH class types (polymorphism)
print("=" * 72)
print("  CUSTOMER PORTFOLIO")
print("=" * 72)
for customer in sorted(portfolio, key=lambda c: c.total_spent(), reverse=True):
    print(f"  {customer.summary()}")

print("\n" + "=" * 72)
print(f"  Total Portfolio Revenue: ${sum(c.total_spent() for c in portfolio):,.2f}")
print(f"  Premium Customers:       {sum(1 for c in portfolio if isinstance(c, PremiumCustomer))}")
print(f"  Standard Customers:      {sum(1 for c in portfolio if type(c) == Customer)}")
print("=" * 72)

========================================================================
  CUSTOMER PORTFOLIO
========================================================================
  [Premium] Alice Johnson (ID: 1001) | Region: Northwest | Total: $1,961.50 | Tier: Platinum | Discount: 20% | Loyalty Bonus: 5% | Member: 6yr
  [Premium] Carol Chen (ID: 1003) | Region: Northwest | Total: $1,300.75 | Tier: Platinum | Discount: 18% | Loyalty Bonus: 3% | Member: 3yr
  [Standard] Bob Martinez (ID: 1002) | Region: Southwest | Total: $421.05 | Tier: Silver | Discount: 5%
  [Standard] David Kim (ID: 1004) | Region: Southeast | Total: $105.00 | Tier: Standard | Discount: 0%

========================================================================
  Total Portfolio Revenue: $3,788.30
  Premium Customers:       2
  Standard Customers:      2
========================================================================