Python Classes and Objects Examples

New to Python and Object-Oriented Programming (OOP)? No worries! This guide will walk you through easy-to-follow examples to help you understand the basics of classes and objects. You'll also learn how to work with methods, attributes, inheritance, and more—step by step!

1. Basic class and object
python
# Example 1: Simple class
class Person:
    def __init__(self, name):
        self.name = name

    def greet(self):
        print("Hello, my name is", self.name)

p = Person("Alice")
p.greet()
2. Class with multiple attributes
python
# Example 2: Class with multiple attributes
class Car:
    def __init__(self, brand, year):
        self.brand = brand
        self.year = year

    def info(self):
        print(f"Brand: {self.brand}, Year: {self.year}")

c = Car("Toyota", 2020)
c.info()
3. Default attribute values
python
# Example 3: Default values
class Animal:
    def __init__(self, species="Dog"):
        self.species = species

    def show(self):
        print("Species:", self.species)

a = Animal()
a.show()
4. Object methods modifying attributes
python
# Example 4: Method modifies attributes
class Counter:
    def __init__(self):
        self.count = 0

    def increment(self):
        self.count += 1

c = Counter()
c.increment()
print("Count:", c.count)
5. Inheritance example
python
# Example 5: Inheritance
class Animal:
    def speak(self):
        print("Animal speaks")

class Dog(Animal):
    def bark(self):
        print("Woof!")

d = Dog()
d.speak()
d.bark()
6. Method overriding
python
# Example 6: Overriding method
class Parent:
    def greet(self):
        print("Hello from Parent")

class Child(Parent):
    def greet(self):
        print("Hello from Child")

c = Child()
c.greet()
7. Using isinstance() and type()
python
# Example 7: isinstance and type
class User:
    pass

u = User()
print(isinstance(u, User))  # True
print(type(u))              # <class '__main__.User'>
8. Class variables vs instance variables
python
# Example 8: Class vs instance variables
class Book:
    category = "Fiction"  # Class variable

    def __init__(self, title):
        self.title = title  # Instance variable

b1 = Book("1984")
b2 = Book("Animal Farm")

print(b1.category, b1.title)
print(b2.category, b2.title)
9. Private attributes (name mangling)
python
# Example 9: Private attribute
class Secret:
    def __init__(self):
        self.__hidden = "This is private"

s = Secret()
print(s._Secret__hidden)  # Accessing private var
10. A simple class-based menu
python
# Example 10: Menu with class
class Menu:
    def display(self):
        print("1. Start")
        print("2. Exit")

    def choose(self, option):
        if option == 1:
            print("Starting...")
        elif option == 2:
            print("Exiting...")
        else:
            print("Invalid option")

m = Menu()
m.display()
m.choose(1)
11. Class with a method that takes parameters
python
# Example 11: Method with parameters
class Calculator:
    def add(self, a, b):
        return a + b

c = Calculator()
print("Sum:", c.add(3, 5))
12. Using @classmethod
python
# Example 12: Class method
class Student:
    school = "Green High"

    def __init__(self, name):
        self.name = name

    @classmethod
    def get_school(cls):
        return cls.school

print(Student.get_school())
13. Using @staticmethod
python
# Example 13: Static method
class MathTools:
    @staticmethod
    def square(n):
        return n * n

print(MathTools.square(4))
14. Simple encapsulation with getters/setters
python
# Example 14: Encapsulation
class BankAccount:
    def __init__(self, balance):
        self.__balance = balance

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

    def get_balance(self):
        return self.__balance

acct = BankAccount(100)
acct.deposit(50)
print("Balance:", acct.get_balance())
15. Object composition example
python
# Example 15: Composition
class Engine:
    def start(self):
        print("Engine started")

class Car:
    def __init__(self):
        self.engine = Engine()

    def drive(self):
        self.engine.start()
        print("Car is moving")

c = Car()
c.drive()
16. Counting instances with class variable
python
# Example 16: Count objects
class Counter:
    count = 0

    def __init__(self):
        Counter.count += 1

print("Initial:", Counter.count)
a = Counter()
b = Counter()
print("After creation:", Counter.count)
17. Simple Inheritance Example
python
# Example 17: Basic inheritance example
class Animal:
    def speak(self):
        print("Animal speaks")

class Dog(Animal):
    def speak(self):
        print("Woof!")

dog = Dog()
dog.speak()  # Output: Woof!
18. Hiding data with name mangling
python
# Example 18: Data hiding
class Account:
    def __init__(self):
        self.__balance = 100

    def get_balance(self):
        return self.__balance

acct = Account()
print(acct.get_balance())
# print(acct.__balance)  # AttributeError
print(acct._Account__balance)
19. Class inheritance with super()
python
# Example 19: super() in inheritance
class Animal:
    def __init__(self, species):
        self.species = species

class Dog(Animal):
    def __init__(self, name):
        super().__init__("Dog")
        self.name = name

d = Dog("Max")
print(d.species, d.name)
20. Inheritance with Constructor Overriding
python
# Example 20: Constructor overriding in inheritance
class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        print(f"{self.name} makes a sound")

class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name)
        self.breed = breed

    def speak(self):
        print(f"{self.name} barks")

dog = Dog("Buddy", "Golden Retriever")
dog.speak()  # Output: Buddy barks
21. Using Encapsulation with Getters and Setters
python
# Example 21: Encapsulation with getters and setters
class Person:
    def __init__(self, name, age):
        self._name = name  # Protected attribute
        self._age = age    # Protected attribute

    # Getter method for name
    @property
    def name(self):
        return self._name

    # Setter method for name
    @name.setter
    def name(self, value):
        self._name = value

    # Getter method for age
    @property
    def age(self):
        return self._age

    # Setter method for age
    @age.setter
    def age(self, value):
        if value < 0:
            print("Age cannot be negative")
        else:
            self._age = value

p = Person("Alice", 30)
print(p.name)  # Output: Alice
p.age = -5      # Output: Age cannot be negative
22. Multiple Inheritance Example
python
# Example 22: Multiple inheritance
class Father:
    def speak(self):
        print("Father speaks")

class Mother:
    def speak(self):
        print("Mother speaks")

class Child(Father, Mother):
    def greet(self):
        print("Hello!")

child = Child()
child.speak()  # Output: Father speaks
child.greet()  # Output: Hello!
23. Using Private Attributes and Methods
python
# Example 23: Using private attributes
class Account:
    def __init__(self, balance):
        self.__balance = balance  # Private attribute

    def deposit(self, amount):
        if amount > 0:
            self.__balance += amount
        else:
            print("Deposit amount must be positive")

    def get_balance(self):
        return self.__balance

acct = Account(1000)
acct.deposit(500)
print(acct.get_balance())  # Output: 1500
24. Inheritance with Method Overriding
python
# Example 24: Method overriding in inheritance
class Vehicle:
    def start(self):
        print("Starting vehicle")

class Car(Vehicle):
    def start(self):
        print("Starting car engine")

car = Car()
car.start()  # Output: Starting car engine
25. Inheritance with `super()`
python
# Example 25: Using 'super()' in inheritance
class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        print(f"{self.name} makes a sound")

class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name)  # Calling the parent class constructor
        self.breed = breed

dog = Dog("Buddy", "Labrador")
dog.speak()  # Output: Buddy makes a sound
26. Class with Private and Protected Members
python
# Example 26: Private and protected members
class Car:
    def __init__(self, make, model):
        self._make = make    # Protected attribute
        self.__model = model  # Private attribute

    def display(self):
        print(f"Make: {self._make}, Model: {self.__model}")

car = Car("abc_maker", "abc_model")
car.display()  # Output: Make: abc_maker, Model: abc_model
27. Abstract Base Class with Encapsulation
python
# Example 27: Abstract Base Class with encapsulation
from abc import ABC, abstractmethod

class Shape(ABC):
    def __init__(self, color):
        self._color = color  # Protected attribute

    @abstractmethod
    def area(self):
        pass

class Circle(Shape):
    def __init__(self, color, radius):
        super().__init__(color)
        self.__radius = radius  # Private attribute

    def area(self):
        return 3.14 * (self.__radius ** 2)

circle = Circle("Red", 5)
print(circle.area())  # Output: 78.5
28. Method Overloading Simulation Using Encapsulation
python
# Example 28: Method overloading simulation using encapsulation
class Calculator:
    def add(self, *args):
        result = 0
        for num in args:
            result += num
        return result

calc = Calculator()
print(calc.add(2, 3))          # Output: 5
print(calc.add(1, 2, 3, 4))    # Output: 10

Keep Practicing Python

Great job learning the basics! To become truly comfortable with Python, the key is practice. Try solving coding challenges, building small projects, and experimenting with different Python concepts beyond OOP, such as functions, loops, and data structures. The more you practice, the more confident you'll become in using Python for real-world applications!