Classes and Objects in Python

Last Updated on July 3, 2023 by Mayank Dham

Classes and Objects in Python is a design philosophy, enabling developers to create modular, reusable, and efficient code. Python, renowned for its object-oriented nature, provides a powerful and intuitive approach to programming through the concept of objects.

In Python, everything is an object. Whether it’s a simple data type like integers and strings or complex structures like classes and functions, everything can be treated as an object. Understanding the essence of objects is crucial for unlocking the full potential of Python and leveraging its object-oriented capabilities

What are Classes in Python?

In Python, a class is a blueprint or a template that defines the characteristics and behavior of a particular object. It is a user-defined data structure that encapsulates data and methods that operate on that data.

Here’s the syntax for defining a class in Python:

class ClassName:
    # Class Variables
    variable_1 = "some value"
    variable_2 = 123

    # Class Methods
    def method_1(self):
        # Method code goes here
        pass

    def method_2(self, parameter_1, parameter_2):
        # Method code goes here
        pass

In this syntax, we define a class called ClassName. Inside the class, we can define class variables and class methods.

Class variables are variables that are shared by all instances of the class. They are defined outside of any method in the class and can be accessed using the class name. In the above example, variable_1 and variable_2 are class variables.

Class methods are methods that operate on the class as a whole, rather than on a specific instance of the class. They are defined inside the class and have the self parameter, which refers to the class instance. In the example above, method_1 and method_2 are class methods.

Here’s an example of a class definition in Python:

class Dog:
    species = "Goldern Retriever"

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

    def bark(self):
        print("Woof!")

In this example, we define a class called Dog. The species variable is a class variable that is shared by all instances of the class. The init method is a special method that is called when a new object is created from the class. It takes in two parameters, name, and breed, and initializes instance variables with the same names. We also define a method called bark that simply prints "Woof!" to the console.

The Self-Parameter

In Python, the self is a special parameter that refers to the instance of the class. It is a convention in Python to use self as the name of the first parameter of instance methods in a class. When you call a method on an instance of a class, Python automatically passes the instance as the first argument to the method.

Here’s an example to illustrate the use of the self parameter in Python:

class MyClass:
    def __init__(self, name):
        self.name = name
    
    def say_hello(self):
        print("Hello, my name is", self.name)

# create an instance of MyClass
my_obj = MyClass("John")

# call the say_hello method on the instance
my_obj.say_hello()

Output:

Hello, my name is John

In this example, we define a class called MyClass with an init method that takes a name parameter and stores it as an instance variable called self.name. We also define a say_hello method that prints a message using the instance variable self.name.

When we create an instance of MyClass and call the say_hello method on it, Python automatically passes the instance as the self parameter to the method.

It’s important to always include self as the first parameter of instance methods in a class. When you call an instance method, you don’t need to explicitly pass the self parameter – Python does this automatically for you. By convention, you should always use the name self for this parameter, although technically you could use any other valid variable name.

Pass Statement in Class

In Python, the pass statement is used as a placeholder when you need a statement in your code that does nothing. It is commonly used in situations where you need to define a block of code that has not yet been implemented, such as a method in a class that you plan to implement later.

Here’s an example of using the pass statement in a class:

class MyClass:
    def method1(self):
        pass

    def method2(self):
        # TODO: implement this method
        pass

In this example, we define a class called MyClass with two methods, method1, and method2. In method1, we simply use the pass statement as a placeholder because we haven’t implemented the method yet. In method2, we use a comment to indicate that we plan to implement the method later, and again use the pass statement as a placeholder.

Using the pass statement in this way allows us to define a class with methods that we plan to implement in the future without causing any syntax errors. It’s a useful tool for managing complex codebases where you may need to define a large number of methods or functions that you plan to implement later.

It’s worth noting that the pass statement is not limited to use in classes – you can use it anywhere in your Python code where you need a statement that does nothing.

Objects in Python

In Python, an object is an instance of a class. It represents a specific instance of a class and can have its own data and behavior.

Here’s an example of creating an object in Python:

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

    def bark(self):
        print("Woof!")

my_dog = Dog("Buddy", "Golden Retriever")

In this example, we define a class called Dog. The init method is a special method that is called when a new object is created from the class. It takes in two parameters, name, and breed, and initializes instance variables with the same names. We also define a method called bark that simply prints "Woof!" to the console.

We then create an object called my_dog from the Dog class with the name "Buddy" and the breed "Golden Retriever". The object has its own data (name and breed) and behavior (the bark method).

Objects can also be used to create more complex programs. For example, we could create a program that simulates a veterinary clinic, where we create objects for each animal and call methods to perform various tasks.

class Animal:
    def __init__(self, name, species):
        self.name = name
        self.species = species
        self.is_healthy = True

    def visit_vet(self):
        self.is_healthy = True

    def display_info(self):
        print(f"{self.name} is a {self.species} and is {'healthy' if self.is_healthy else 'sick'}.")

dog = Animal("Spikes", "Dog")
cat = Animal("Tom", "Cat")

dog.visit_vet()
cat.is_healthy = False

dog.display_info()
cat.display_info()

Output:

Spikes is a Dog and is healthy.
Tom is a Cat and is sick.

In this example, we define an Animal class with an init method, a visit_vet method to simulate a visit to the veterinarian, and a display_info method to display information about the animal. We then create objects for a dog and a cat, and call methods to perform various tasks. The objects have their own data (name, species, and health status) and behavior (the visit_vet and display_info methods).

Class Attributes in Python

In Python, class attributes are variables that are shared by all instances of a class. They are defined at the class level and can be accessed by all instances of the class. There are three types of class attributes in Python:

Class-level attributes: These are defined at the class level and are shared by all instances of the class. They are defined outside of any method in the class and are usually given a default value. Class-level attributes are accessed using the class name and the dot operator.

Here’s an example of a class-level attribute:

class Circle:
    pi = 3.14

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

    def circumference(self):
        return 2 * Circle.pi * self.radius

In this example, the pi attribute is a class-level attribute and is accessed using the Circle class name.

Instance-level attributes: These are defined inside the init method and are unique to each instance of the class. They are accessed using the instance name and the dot operator.

Here’s an example of an instance-level attribute:

class Rectangle:
    def __init__(self, length, width):
        self.length = length
        self.width = width

    def area(self):
        return self.length * self.width

In this example, the length and width attributes are instance-level attributes and are unique to each instance of the Rectangle class.

Private class attributes: These are defined with double underscores ( __ ) before the attribute name. They cannot be accessed directly from outside the class and can only be accessed using special methods like getters and setters.

Here’s an example of a private class attribute:

class BankAccount:
    __interest_rate = 0.05

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

    def get_interest(self):
        return self.balance * BankAccount.__interest_rate

In this example, the __interest_rate attribute is a private class attribute and cannot be accessed directly from outside the BankAccount class.

Class Methods in Python

In Python, classes can have three types of methods: instance methods, class methods, and static methods.

Instance Method:
An instance method is a method that operates on the instance of a class. It takes the instance itself (self) as its first parameter and can access the instance variables. Here’s an example of an instance method:

class MyClass:
    def my_instance_method(self):
        print("This is an instance method.")

# create an object of the class
obj = MyClass()

# call the instance method
obj.my_instance_method()

Output:

This is an instance method.

Class Method:
A class method is a method that operates on the class itself rather than an instance of the class. It takes the class (cls) as its first parameter and can access class variables. Here’s an example of a class method:

class MyClass:
    class_var = 0
    
    @classmethod
    def my_class_method(cls):
        cls.class_var += 1
        print("This is a class method.", cls.class_var)

# call the class method
MyClass.my_class_method()

Output:

This is a class method 1

Static Method:
A static method is a method that does not operate on either the class or instance of a class. It is similar to a regular function, but it is defined inside a class for organization purposes. Here’s an example of a static method:

class MyClass:
    @staticmethod
    def my_static_method():
        print("This is a static method.")

# call the static method
MyClass.my_static_method()

Output:

This is a static method.

How To Delete an Object in Python

To delete an object of a class in Python, you can use the del statement followed by the name of the object you want to delete. Here is an example:

class MyClass:
    def __init__(self, x):
        self.x = x

# create an object of the class
obj = MyClass(5)

# delete the object
del obj

In the above example, an object obj of the class MyClass is created, and then it is deleted using the del statement. Once the object is deleted, you cannot use it anymore, and any attempt to access it will result in an error.

Summary

• Classes and objects are an essential part of object-oriented programming in python.
• A class is a blueprint for creating objects with certain properties and behaviors. An object is an instance of a class that has its own set of properties and can perform the behaviors defined in the class.
• Class attributes and methods are used to define and operate on the class as a whole, while instance attributes and methods are used to operate on specific instances of the class.
• The self-parameter is used to reference the instance of the class in instance methods.
• The pass statement is used as a placeholder in code where a statement is required, but no action needs to be taken.
• To remove an object in Python, one can make use of the ‘del’ keyword followed by the object name. After deleting the object, the reference to it is removed, which enables the garbage collector to reclaim the memory that was being used by the object.

Conclusion
In conclusion, understanding classes and objects is pivotal for mastering object-oriented programming in Python. Through this article, we have explored the foundational concepts of classes and objects, their relationship, and the benefits they bring to Python development. Through this article, we will have clear idea about, what is objects in python.

We learned that classes serve as blueprints or templates for creating objects, allowing us to define their attributes and methods. Objects, on the other hand, are specific instances of classes, representing unique entities with their own data and behavior.

FAQs about Classes and Objects in Python

Here are some Frequently Asked Questions on classes and objects in python

Q1 – How do you define a class in Python?
To define a class in Python, you use the class keyword followed by the name of the class, and then define the attributes and methods of the class within the class definition.

Q2 – What is an object in Python?
An object is an instance of a class. It is created by calling the class as if it were a function, passing any necessary arguments to the init method defined in the class.

Q3 – How do you create an object in Python?
To create an object in Python, you call the class as if it were a function, passing any necessary arguments to the init method defined in the class.

Q4 – What is the difference between class and instance methods in Python?
A class method is a method that operates on the class as a whole, rather than on a specific instance of the class. It is defined using the @classmethod decorator. An instance method is a method that operates on a specific instance of the class and is defined within the class without any special decorators.

Q5 – What is the difference between a class and an object in Python?
A class is a template for creating objects, while an object is an instance of a class. A class defines the properties and behaviors that its objects will have, while objects have their own set of properties and can perform the behaviors defined in the class.

Q6 – How do you delete an object in Python?
To delete an object in Python, you use the del keyword followed by the name of the object you want to delete.