Private attributes in Python

Introduction

Private attributes help keep some parts of an object hidden so others can't change them by mistake.

When you want to protect important data inside an object from being changed directly.

When you want to control how data inside an object is accessed or modified.

When you want to hide details that users of your class don't need to see.

When you want to avoid accidental changes to internal variables.

When you want to make your code safer and easier to maintain.

Syntax

Python

class ClassName:
    def __init__(self):
        self.__private_attribute = None

Private attributes start with two underscores __.

This makes Python change the name internally to avoid easy access from outside.

Examples

This creates a private attribute __speed inside the Car class.

Python

class Car:
    def __init__(self, speed):
        self.__speed = speed

Private attribute __name is accessed safely using a method get_name.

Python

class Person:
    def __init__(self, name):
        self.__name = name

    def get_name(self):
        return self.__name

Sample Program

This program shows a private attribute __balance in a BankAccount class. It can only be changed by methods inside the class. Trying to access it directly causes an error.

Python

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

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

    def get_balance(self):
        return self.__balance

account = BankAccount(100)
print(account.get_balance())  # prints 100
account.deposit(50)
print(account.get_balance())  # prints 150

# Trying to access private attribute directly
try:
    print(account.__balance)
except AttributeError as e:
    print(e)

Important Notes

Private attributes are not truly hidden but renamed internally (name mangling).

You can still access them using _ClassName__attribute but it is not recommended.

Use private attributes to protect important data and keep your code clean.

Summary

Private attributes start with two underscores __ to hide them.

They help protect data inside objects from outside changes.

Access private attributes using methods inside the class.