Encapsulation

Encapsulation means controlling how an object's internal state can be read or changed — instead of letting any code reach in and set account.balance = -500 directly, you expose a controlled interface (methods, or a @property) that can enforce rules.

Python doesn't have true "private" attributes, but the convention _balance (leading underscore) signals "internal, don't touch directly from outside" even though nothing technically stops you:

class BankAccount:
    def __init__(self, balance=0):
        self._balance = balance   # "private by convention"

    @property
    def balance(self):
        return self._balance   # read-only access from outside

The real value of encapsulation shows up in a method that VALIDATES before changing state — logic a raw public attribute could never enforce:

def withdraw(self, amount):
    if amount > self._balance or amount < 0:
        return False   # reject, state unchanged
    self._balance -= amount
    return True

If balance were just a plain public attribute, nothing would stop account.balance -= 999999, overdrawing the account with no validation at all. Routing every change through a method (or a @property setter) means the "can never go negative" rule lives in exactly ONE place, guaranteed to run every single time the balance changes.