Composition over Inheritance: How to Build a Wallet Account in Python

class WalletAccount:
    def __init__(self, owner, balance=0.0):
        self.owner = owner
        self.balance = balance

    def deposit(self, amount):
        if amount <= 0:
            raise ValueError("Deposit must be positive")
        self.balance += amount
        return self.balance

    def withdraw(self, amount):
        if amount <= 0:
            raise ValueError("Withdrawal must be positive")
        if amount > self.balance:
            raise ValueError("Insufficient funds")
        self.balance -= amount
        return self.balance


def transfer(sender, receiver, amount):
    sender.withdraw(amount)
    receiver.deposit(amount)
    return f"Transferred ${amount:.2f} from {sender.owner} to {receiver.owner}"


class AuditedWallet:
    def __init__(self, wallet):
        self._wallet = wallet
        self.transactions = []

    def deposit(self, amount):
        result = self._wallet.deposit(amount)
        self.transactions.append(f"Deposited ${amount:.2f}")
        return result

    def withdraw(self, amount):
        result = self._wallet.withdraw(amount)
        self.transactions.append(f"Withdrew ${amount:.2f}")
        return result

    @property
    def balance(self):
        return self._wallet.balance

    @property
    def owner(self):
        return self._wallet.owner


if __name__ == "__main__":
    alice = AuditedWallet(WalletAccount("Alice", 100.0))
    bob = WalletAccount("Bob", 50.0)

    alice.withdraw(30.0)
    transfer(alice, bob, 20.0)

    print(f"Alice balance: ${alice.balance:.2f}")
    print(f"Bob balance: ${bob.balance:.2f}")
    print(f"Audit log for Alice: {alice.transactions}")