Project: A Safe Bank Account

Time to combine everything: __init__, methods, a @property, and raising an exception to enforce a rule. You will build a small BankAccount that refuses to go into the red.

Recall how to raise an error when an input is invalid:

def withdraw(amount):
    if amount > 100:
        raise ValueError("not enough funds")

And how a property exposes a computed or guarded value as a plain attribute:

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

Your account will track a running balance privately in self._balance, expose it read-only through a balance property, and reject any withdrawal that would overdraw the account by raising ValueError. This is the pattern real systems use: the data is protected, and the rules live with the object that owns the data.