What is encapsulation?

Encapsulation bundles data with the methods that operate on it, and restricts direct access to internal state so invariants stay safe.

Python does not have hard private fields like some languages. It uses conventions:

• public: normal names
• _internal: "protected by convention" (internal use)
• __mangled: name-mangled to _Class__attr to avoid subclass clashes (not true security)

Properties (@property) expose controlled getters/setters.

class BankAccount:
    def __init__(self, balance: float):
        self._balance = balance

    @property
    def balance(self) -> float:
        return self._balance

    def deposit(self, amount: float) -> None:
        if amount <= 0:
            raise ValueError("amount must be positive")
        self._balance += amount

acct = BankAccount(100)
acct.deposit(50)
print(acct.balance)
# acct.balance = 0   # AttributeError if only getter defined

Interview tip: Emphasize convention + API design over "Python has private keywords." Encapsulation is about protecting invariants, not hiding bytes from determined users.