Introduction

So far, you have accessed object data directly using attributes such as:

student.name
player.health

While this works, it is often not good design.

Encapsulation is an object-oriented principle that:

  • Protects data inside an object
  • Controls how data can be accessed or changed
  • Makes programs safer and easier to maintain

In this lesson, you will learn:

  • Why direct access to attributes can be a problem
  • How to make attributes “private”
  • How to use getter and setter methods

Why Encapsulation Matters

Imagine a bank account where anyone can do this:

account.balance = -1000

This should never be allowed.

Encapsulation solves this by:

  • Hiding the data
  • Forcing all changes to go through methods

Private Attributes in Python

Python does not have true private variables, but by convention we use a double underscore:

self.__balance

This tells other programmers:

  • “Do not access this directly”
  • “Use methods instead”

Example: Bank Account with Encapsulation 

class BankAccount:
    def __init__(self, owner, balance):
        self.owner = owner
        self.__balance = balance

    def get_balance(self):
        return self.__balance

    def deposit(self, amount):
        if amount > 0:
            self.__balance += amount

    def withdraw(self, amount):
        if amount <= self.__balance:
            self.__balance -= amount

Notice:

  • The balance cannot be accessed directly
  • All changes go through methods

Predict:

What do you think will happen when this code is run?

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

account = BankAccount(100)
print(account.__balance)

Think about:

  • Is __balance accessible outside the class?
  • What error might Python raise?

Run:

Run the program below to check your prediction.

Investigate:

Now let’s access the balance the correct way.

Try this:

  • Add a method called get_balance()
  • Return the value of __balance
  • Use the method to print the balance

Think about:

  • Why is this safer than direct access?
  • What could we add later without changing the rest of the program?

Modify:

The following program tries to protect the balance, but it contains mistakes.

Fix the code so:

  • The balance is private
  • Deposits work correctly
  • The balance can be read safely

The problem

  • The attribute is not private
  • The balance is not updated
  • self is missing
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