Summary - Encapsulation

Combine @property, @dataclass and __slots__ to write an Account class.

Summary - Encapsulation

In this group we covered encapsulation: the _balance convention, a getter with @property, a setter with @x.setter, lean classes with @dataclass and layout limits with __slots__.

Encapsulation protects inner data and keeps the outer interface stable. @property + a setter validate during assignment. @dataclass simplifies boilerplate. __slots__ gives memory and layout control. Now we'll combine these into an Account class.

Exercise Combine the Account class

Define the Account class. Add __init__(self, balance) with self._balance = balance. Add @property with def balance(self): and return self._balance. Add @balance.setter with def balance(self, value):; in the body write if value < 0: and return, then self._balance = value. Then call a = Account(100) and print(a.balance).

Show example solution

# Combine the Account class
class Account:
    def __init__(self, balance):
        self._balance = balance
    @property
    def balance(self):
        return self._balance
    @balance.setter
    def balance(self, value):
        if value < 0:
            return
        self._balance = value

a = Account(100)
print(a.balance)

Test yourself

What is done inside a setter?
- The class is deleted
- A new instance is created
- The assigned value is validated and written to inner data
- The class name is changed
Show answer

The assigned value is validated and written to inner data — The setter validates the value and writes it to the inner attribute.
Match the concepts

_balance

Private attribute
@property

Getter
@balance.setter

Setter

Complete the getter body

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

Show answer

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

Next lesson: @staticmethod

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