Python Core | VoidX Academy

13. Python Classes and Objects

Object-Oriented

Python Classes and Objects

Python is an Object-Oriented Programming (OOP) language. Almost everything in Python is an object, meaning it has properties (data) and methods (actions it can perform). A Class is like an object constructor, or a blueprint for creating objects.

Instead of writing messy, disconnected variables and functions, classes allow you to group related data and functions together into a single organized entity. This makes your code modular, reusable, and much easier to maintain.

Creating a Class

To create a class, use the keyword class. By convention, class names in Python always start with a capital letter (PascalCase).

class Blueprint:
    x = 5

print(Blueprint)

Output<class '__main__.Blueprint'>

Creating an Object

Once you have a class (the blueprint), you can use it to build actual objects. This process is called instantiation. You create an object by calling the class name as if it were a function.

class Blueprint:
    x = 5

# Creating an object named 'my_object'
my_object = Blueprint()

print(my_object.x)

Output5

The init() Function

To understand the true power of classes, you must master the built-in __init__() function. All classes have this function, which is always executed automatically exactly when the class is being initiated.

Use the __init__() function to assign initial values to object properties.

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

user1 = Person("Alice", 30)
user2 = Person("Bob", 25)

print(user1.name)
print(user2.age)

OutputAlice 25

The str() Function

The __str__() function controls what should be returned when the class object is represented as a string. If you do not define it, printing the object just gives you a cryptic memory address.

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

    def __str__(self):
        return f"{self.name} is {self.age} years old"

user = Person("Charlie", 40)
print(user)

OutputCharlie is 40 years old

Object Methods

Objects can also contain methods. Methods in objects are simply functions that belong to the object. They define the actions the object can perform.

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

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

user = Person("Alice")
user.greet()

OutputHello, my name is Alice

The self Parameter

The self parameter is a reference to the current instance of the class. It is used to access variables and methods that belong to the class.

It absolutely must be the first parameter of any instance method in the class.

class Car:
    def __init__(self, brand):
        self.brand = brand

    def honk(self):
        print(f"The {self.brand} goes beep!")

my_car = Car("Toyota")
my_car.honk()

OutputThe Toyota goes beep!

💡Best Practice: Always name the first parameter self. Even though Python allows other names, using "self" is a strict convention among Python developers.

Modifying Object Properties

You can easily modify properties on objects after they have been created using standard dot notation.

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

user = Person("Bob", 25)
print(user.age)

# Modifying the property
user.age = 26
print(user.age)

Output25 26

Deleting Object Properties

If you no longer need a property on a specific object instance, you can delete it using the del keyword.

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

user = Person("Bob", 25)

del user.age

try:
    print(user.age)
except AttributeError as e:
    print(f"Error: {e}")

OutputError: 'Person' object has no attribute 'age'

Deleting Objects Entirely

You can also delete an entire object outright if you are completely finished with it. Use the del keyword followed by the object name.

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

user = Person("Alice")
print(user.name)

del user

try:
    print(user.name)
except NameError as e:
    print(f"Error: {e}")

OutputAlice Error: name 'user' is not defined

The pass Statement in Classes

Class definitions cannot be empty. If you are scaffolding out an application and need a class structure but have no content for it yet, put in the pass statement.

class EmptyBlueprint:
    pass

print("Program runs successfully even with an empty class!")

OutputProgram runs successfully even with an empty class!

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Ready to test your understanding of 13. Python Classes and Objects?

12. Python Functions

14. Python Inheritance

13. Python Classes and Objects

Object-Oriented

Python Classes and Objects

Creating a Class

To create a class, use the keyword class. By convention, class names in Python always start with a capital letter (PascalCase).

class Blueprint:
    x = 5

print(Blueprint)

Output<class '__main__.Blueprint'>

Creating an Object

Once you have a class (the blueprint), you can use it to build actual objects. This process is called instantiation. You create an object by calling the class name as if it were a function.

class Blueprint:
    x = 5

# Creating an object named 'my_object'
my_object = Blueprint()

print(my_object.x)

Output5

The init() Function

Use the __init__() function to assign initial values to object properties.

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

user1 = Person("Alice", 30)
user2 = Person("Bob", 25)

print(user1.name)
print(user2.age)

OutputAlice 25

The str() Function

The __str__() function controls what should be returned when the class object is represented as a string. If you do not define it, printing the object just gives you a cryptic memory address.

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

    def __str__(self):
        return f"{self.name} is {self.age} years old"

user = Person("Charlie", 40)
print(user)

OutputCharlie is 40 years old

Object Methods

Objects can also contain methods. Methods in objects are simply functions that belong to the object. They define the actions the object can perform.

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

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

user = Person("Alice")
user.greet()

OutputHello, my name is Alice

The self Parameter

The self parameter is a reference to the current instance of the class. It is used to access variables and methods that belong to the class.

It absolutely must be the first parameter of any instance method in the class.

class Car:
    def __init__(self, brand):
        self.brand = brand

    def honk(self):
        print(f"The {self.brand} goes beep!")

my_car = Car("Toyota")
my_car.honk()

OutputThe Toyota goes beep!

💡Best Practice: Always name the first parameter self. Even though Python allows other names, using "self" is a strict convention among Python developers.

Modifying Object Properties

You can easily modify properties on objects after they have been created using standard dot notation.

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

user = Person("Bob", 25)
print(user.age)

# Modifying the property
user.age = 26
print(user.age)

Output25 26

Deleting Object Properties

If you no longer need a property on a specific object instance, you can delete it using the del keyword.

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

user = Person("Bob", 25)

del user.age

try:
    print(user.age)
except AttributeError as e:
    print(f"Error: {e}")

OutputError: 'Person' object has no attribute 'age'

Deleting Objects Entirely

You can also delete an entire object outright if you are completely finished with it. Use the del keyword followed by the object name.

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

user = Person("Alice")
print(user.name)

del user

try:
    print(user.name)
except NameError as e:
    print(f"Error: {e}")

OutputAlice Error: name 'user' is not defined

The pass Statement in Classes

Class definitions cannot be empty. If you are scaffolding out an application and need a class structure but have no content for it yet, put in the pass statement.

class EmptyBlueprint:
    pass

print("Program runs successfully even with an empty class!")

OutputProgram runs successfully even with an empty class!

Knowledge Check

Ready to test your understanding of 13. Python Classes and Objects?

12. Python Functions

14. Python Inheritance

13. Python Classes and Objects

Python Classes and Objects

Creating a Class

Creating an Object

The __init__() Function

The __str__() Function

Object Methods

The self Parameter

Modifying Object Properties

Deleting Object Properties

Deleting Objects Entirely

The pass Statement in Classes

Knowledge Check

13. Python Classes and Objects

Python Classes and Objects

Creating a Class

Creating an Object

The __init__() Function

The __str__() Function

Object Methods

The self Parameter

Modifying Object Properties

Deleting Object Properties

Deleting Objects Entirely

The pass Statement in Classes

Knowledge Check

The init() Function

The str() Function

The init() Function

The str() Function