Classes In Python | Objects, Creation, Working, & More (+Examples)

0 min read

Python is an object-oriented programming (OOP) language, and at the heart of OOP lie classes and objects. A class is a blueprint for creating objects, allowing us to structure code efficiently, reduce redundancy, and build scalable applications. An object is an instance of a class– a concrete entity that holds data and behaviors defined by the class.

In this article, we’ll explore the concept of classes in Python, covering how to define them, their components, and how objects are created and interact with them. We’ll also explore the usage of classes and objects in Python classes, key OOP principles, real-world applications, and common pitfalls to avoid when designing classes in Python programs.

What Are Classes In Python?

A class in Python is a blueprint for creating objects. It defines a set of attributes (data) and methods (functions) that the objects created from the class will have.

Think of it as a template, just like a cookie cutter that shapes multiple cookies; a class allows us to create multiple objects with shared properties and behavior. In simple terms, a class is like a template, and the objects created from it are instances that follow its design. Now, let’s look at a few key features of Python classes.

Key Features of Classes in Python

• Encapsulation– Groups related data and behavior together.
• Reusability– Enables code reuse by defining once and creating multiple instances.
• Modularity– Helps structure large programs efficiently.

Real-Life Analogy

Imagine a car manufacturing blueprint. The blueprint defines features like color, engine type, and brand but doesn't create an actual car. 

• When a car is built using that blueprint, it becomes an object of the Car class. 
• Each car object may have different values for color or engine type, but all follow the same design.

This is how every object in Python is created from a class, making classes the backbone of object-oriented programming. Next, let’s see how to define a class in Python.

How To Create/Define Classes In Python?

In Python programming, a class is defined using the class keyword, followed by the class name and a colon. Inside the class, we define attributes (variables) and methods (functions) that describe its behavior.

Syntax For Defining Class In Python

class ClassName:  
    # Class attributes and methods go here  

Here,

• The class keyword marks the beginning of a class definition whose name is given by the term ClasName. Note that this name should follow PascalCase (e.g., Student, Car, BankAccount).
• The indented body after the colon is the class body, which contains attributes, methods, object definitions, and more.

Example: Creating A Simple Class In Python

Continuing with our car manufacturing blueprint example above, let’s create a simple Python program example that translates it into code. Here, we will have a class Car with an attribute and a method.

Code Example:

            class Car:
    def __init__(self, brand):
        self.brand = brand # Instance attribute 
    def show_brand(self):
        print("Car brand:", self.brand)

# Creating an object of the class 
car1 = Car("Toyota") 

# Calling the method 
car1.show_brand()
          

Y2xhc3MgQ2FyOgogICAgZGVmIF9faW5pdF9fKHNlbGYsIGJyYW5kKToKICAgICAgICBzZWxmLmJyYW5kID0gYnJhbmQgIyBJbnN0YW5jZSBhdHRyaWJ1dGXCoAogICAgZGVmIHNob3dfYnJhbmQoc2VsZik6CiAgICAgICAgcHJpbnQoIkNhciBicmFuZDoiLCBzZWxmLmJyYW5kKQoKIyBDcmVhdGluZyBhbiBvYmplY3Qgb2YgdGhlIGNsYXNzwqAKY2FyMSA9IENhcigiVG95b3RhIinCoAoKIyBDYWxsaW5nIHRoZSBtZXRob2TCoApjYXIxLnNob3dfYnJhbmQoKQ==

Output:

Car brand: Toyota

Code Explanation:

In the simple Python code example:

1. Defining the class: We use the class keyword (i.e., ‘class Car:’) to define the class with the name Car.
2. Inside, we define a method __init__() that initializes the object with the brand attribute. In other languages, this is also referred to as the class constructor.
3. We also define the function, show_brand() which displays the brand name using the print() function.
4. Creating an object: Then, we create an object/ instance of the class with the car1 and use the Car(“Toyota”) notation to initialize its brand attribute.
5. Then, we print the brand name by calling the show_brand() method on the object car1.

Note: If a class has no attributes or methods yet, you can use the pass statement to avoid syntax errors:

class EmptyClass:
    pass  # Placeholder for future implementation

Components Of Classes In Python

A class in Python consists of several key components that define its structure and behavior. Let’s break them down:

1. Attributes (Variables inside a Class): Attributes store data related to the class and its objects.
Types of Attributes:

• Instance Attributes – Belong to an object and are unique to each instance.
• Class Attributes – Shared among all objects of the class.

Example:

class Student:
    school = "Unstop Academy"  # Class attribute
    def __init__(self, name, age):
        self.name = name  # Instance attribute
        self.age = age    # Instance attribute

Here, school is a class attribute (same for all students), and name and age are instance attributes (specific to each student).

2. Methods (Functions inside a Class): Methods define behavior for class objects or perform operations using them. They can modify or access attributes.

Example:

class Student:
    def __init__(self, name):
        self.name = name 
    def greet(self):
        print(f"Hello, my name is {self.name}!")  

Here, greet() is a method that prints a greeting.

3. The __init__() Method (Constructor)

The __init__() method is a special method used to initialize objects. It gets called automatically when an object is created.

Example:

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

Here, the __init__() method ensures every student object has a name when created.

4. The self Parameter: This parameter represents the current object instance and allows access to instance attributes and methods.

This is how we define and instantiate classes in Python! We will discuss the __init__() method, object creation, self parameter, and class methods in detail in the later sections.

Naming Conventions For Classes In Python

Following consistent naming conventions makes your code readable, maintainable, and Pythonic. Here are the key guidelines:

1. Use PascalCase for Class Names: Class names should follow PascalCase (UpperCamelCase), where each word starts with an uppercase letter and there are no underscores.

2. Avoid Built-in Keywords & Special Characters: Do not use Python's built-in keywords (e.g., class, int, list, etc.) or special characters in class names. In the incorrect example below, we use the list keyword, which signifies the Python list structures.

3. Use Singular Nouns for Class Names: Class names should usually be singular because each class represents a single blueprint for objects.

4. Prefix Abstract Base Classes with ABC (Optional but Recommended for Clarity): If creating an Abstract Base Class (ABC), prefix the name with "ABC" to indicate its purpose.

Example:

from abc import ABC
class ABCVehicle(ABC):  # Abstract Base Class
    #Class Body

5. Private Classes Should Start with an Underscore (_): In Python, a class name starting with an underscore indicates that it is intended for internal use only.

Example:

class _InternalHelper:
    #Class Body

Quick Question!

What Is An Object In Python?

An object is an instance of a class. While a class acts as a blueprint, an object is a real-world entity created from that blueprint. Think of a class as a recipe for a cake 🍰 that lists the ingredients and steps to make a cake.
An object is the actual cake made using that recipe. You can make multiple cakes (objects) from the same recipe (class).

Key Characteristics Of Objects

• Objects store data (attributes) and behavior (methods).
• Multiple objects can be created from the same class, each with different attributes.
• Objects allow code reusability and modularity.

How To Create Objects In Python Classes?

In Python, creating an object (also referred to as instantiating a class) is simple–you call the class name as if it were a function. This automatically invokes the __init__() method (constructor) to initialize the object.

Syntax For Creating An Object In Python

object_name = ClassName(arguments)

Here,

• ClassName is the name of the class you are instantiating, i.e., the object belongs to that class.
• The arguments are the values passed to the __init__() method (if any) to assign to the attributes of the object.

We’ve already seen how to create an object in Python programs when describing how to create classes in the example (previous section). But let’s look at another Python program example to cement how to create objects.

Example: Creating Objects In Python

            class Student:
    def __init__(self, name, age): # Constructor
        self.name = name # Instance attribute
        self.age = age # Instance attribute

    def introduce(self):
        print(f"My name is {self.name}, and I am {self.age} years old.")

# Creating objects of the Student class
student1 = Student("Amit", 21)
student2 = Student("Priya", 22)

# Calling the introduce() method
student1.introduce()
student2.introduce()
          

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

Output:

My name is Amit, and I am 21 years old.
My name is Priya, and I am 22 years old.

Code Explanation:

In the Python code example, we define a class named Student.

• Class Definition: The class contains an __init__() method, whose purpose is to initialize two attributes, i.e., name and age. This shows that objects of the Student class can have these two attributes.
• It also contains an introduce() method (class method) that displays the student’s information using the f-strings method to format it as needed.
• Creation of Objects: In the main part, we create two objects of type Student (i.e., belonging to the Student class).
• We use the class name (Student) and the values we want to assign to the object attributes (arguments). 
• For the first object, i.e., student1, we pass the values “Amit" and 21 as arguments.
• For the second object, i.e., student2, we pass the values "Priya" and 22 to instantiate the class object.
• Using Objects to Call Methods: Next, we call the introduce() method twice, i.e., once on each object. 
• Here, we use the object name followed by the dot operator and then the method name.

Creating Multiple Objects In Python Classes

The process of creating multiple objects remains the same as creating a single object. You only have to repeat the syntax for every new object you want to create. As in the example above, we created two objects for the Student class. 

The process of creating multiple objects for classes in Python is made simple using the __init__() method. However, it is still possible to create multiple objects/initialize the class in the absence of this method. We will discuss more on this in a later section. 

Modifying & Deleting Objects In Python Classes

Once an object is created, we can modify its attributes dynamically or even delete attributes and objects when they are no longer needed. In this section, we will discuss how to make these modifications on objects and classes in Python programs with examples.

Modifying Object Attributes In Python Classes

Once an object has been created and you have assigned the initial values for its attributes, you can still modify any of the values by accessing the object and the respective attribute using the dot notation. 

That is, you have to specify the object and attribute, say object1.attribute2, and then assign a new value as needed. The example Python program given below highlights how this can be done.

Code Example:

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

    def introduce(self):
        print(f"My name is {self.name}, and I am {self.age} years old.")

# Creating an object
student1 = Student("Amit", 21)
student1.introduce()

# Modifying attributes
student1.age = 22
student1.introduce()
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lLCBhZ2UpOgogICAgICAgIHNlbGYubmFtZSA9IG5hbWUKICAgICAgICBzZWxmLmFnZSA9IGFnZQoKICAgIGRlZiBpbnRyb2R1Y2Uoc2VsZik6CiAgICAgICAgcHJpbnQoZiJNeSBuYW1lIGlzIHtzZWxmLm5hbWV9LCBhbmQgSSBhbSB7c2VsZi5hZ2V9IHllYXJzIG9sZC4iKQoKIyBDcmVhdGluZyBhbiBvYmplY3QKc3R1ZGVudDEgPSBTdHVkZW50KCJBbWl0IiwgMjEpCnN0dWRlbnQxLmludHJvZHVjZSgpCgojIE1vZGlmeWluZyBhdHRyaWJ1dGVzCnN0dWRlbnQxLmFnZSA9IDIyCnN0dWRlbnQxLmludHJvZHVjZSgp

Output:

My name is Amit, and I am 21 years old.
My name is Amit, and I am 22 years old.

Code Explanation:

Just like in the main object example, we define a Student class with two attributes, an __init__() method and an introduce() method.

• Creating an object: Then, we create an object named student1 and initialize its attributes with the values name “Amit” and age 22.
• We then call the introduce() method to display the information. 
• Modifying an attribute: After that, we modify the age attribute of the object, i.e., student1.age with the value 22.
• Then, we again call the introduce() method to print the student information. The output shows that the age attribute has been modified.

Adding New Attributes To An Object In Python Classes

Python allows adding attributes dynamically to an object even if they were not defined in the class. Note that this additional will affect only the respective object and not all objects. In the example below, we have illustrated how to add an attribute to an object after it was created.

Code Example:

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

# Creating an object
student1 = Student("Amit", 21)

# Adding a new attribute dynamically
student1.city = "Delhi"

# Accessing the new attribute
print(student1.city)
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lLCBhZ2UpOgogICAgICAgIHNlbGYubmFtZSA9IG5hbWUKICAgICAgc2VsZi5hZ2UgPSBhZ2UKCiMgQ3JlYXRpbmcgYW4gb2JqZWN0CnN0dWRlbnQxID0gU3R1ZGVudCgiQW1pdCIsIDIxKQoKIyBBZGRpbmcgYSBuZXcgYXR0cmlidXRlIGR5bmFtaWNhbGx5CnN0dWRlbnQxLmNpdHkgPSAiRGVsaGkiCgojIEFjY2Vzc2luZyB0aGUgbmV3IGF0dHJpYnV0ZQpwcmludChzdHVkZW50MS5jaXR5KQ==

Output:

Delhi

Code Explanation:

In this example Python code, we again define the student class, where each object can have two attributes: name and age.

• We create an object student1, with attribute values “Amit” and 21.
• The city attribute was not defined in the original class definition.
• We added it dynamically using the object name and dot operator, i.e., student1.city = "Delhi".
• Now, student1 has the city attribute, but other instances of Student will not have this attribute unless explicitly assigned.

Note: While Python allows this, adding attributes dynamically is not always a good practice, as it can lead to inconsistent object structures across instances.

Deleting An Attribute From An Object In Python Classes

You can remove an object's attribute using the del keyword. The example below highlights how this can be done.

Code Example:

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

# Creating an object
student1 = Student("Amit", 21)

# Deleting an attribute
del student1.age

# Trying to access the deleted attribute will cause an error
print(student1.age)
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lLCBhZ2UpOgogICAgICAgIHNlbGYubmFtZSA9IG5hbWUKICAgICAgc2VsZi5hZ2UgPSBhZ2UKCiMgQ3JlYXRpbmcgYW4gb2JqZWN0CnN0dWRlbnQxID0gU3R1ZGVudCgiQW1pdCIsIDIxKQoKIyBEZWxldGluZyBhbiBhdHRyaWJ1dGUKZGVsIHN0dWRlbnQxLmFnZQoKIyBUcnlpbmcgdG8gYWNjZXNzIHRoZSBkZWxldGVkIGF0dHJpYnV0ZSB3aWxsIGNhdXNlIGFuIGVycm9yCnByaW50KHN0dWRlbnQxLmFnZSk=

Output:

AttributeError: 'Student' object has no attribute 'age'

Code Explanation:

We continue with the Student class example. After creating the object student1, we delete one of its attributes as follows:

• We used del student1.age to remove the age attribute.
• After this, when we try to access student1.age, it results in an AttributeError.
• Note again that this affects only that object (here student1) and will not affect other class objects (if any).

Use Case: This is useful when you need to free memory or remove unnecessary attributes dynamically.

Deleting An Entire Object

Just like we deleted a single attribute of an object, we can use the del keyword to completely delete an object. The syntax for this will be: del object_name.

Code Example:

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

# Creating an object
student1 = Student("Amit", 21)

# Deleting the entire object
del student1

# Trying to access the deleted object will cause an error
print(student1)
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lLCBhZ2UpOgogICAgICAgIHNlbGYubmFtZSA9IG5hbWUKICAgICAgICBzZWxmLmFnZSA9IGFnZQoKIyBDcmVhdGluZyBhbiBvYmplY3QKc3R1ZGVudDEgPSBTdHVkZW50KCJBbWl0IiwgMjEpCgojIERlbGV0aW5nIHRoZSBlbnRpcmUgb2JqZWN0CmRlbCBzdHVkZW50MQoKIyBUcnlpbmcgdG8gYWNjZXNzIHRoZSBkZWxldGVkIG9iamVjdCB3aWxsIGNhdXNlIGFuIGVycm9yCnByaW50KHN0dWRlbnQxKQ==

Output:

NameError: name 'student1' is not defined

Code Explanation:

In the sample Python code, we continue with the student class and create an object student1.

• Then, we use del student1, which removes the object from memory.
• Accessing student1 after deletion raises a NameError because the variable no longer exists.

Quick Question!

The __init__() Method In Python Classes

The __init__() method is the constructor for classes in Python. It is a special method that gets called automatically when you create an object for a class and allows us to initialize the object’s attributes with specific values.

Think of it like checking into a hotel:

• You provide your name and ID at the reception.
• The hotel assigns you a room with your details.
• Every guest (object) gets their own room (unique attributes).

The __init__() method works the same way. It assigns initial values to object attributes when an object is created.

Syntax Of __init__()

class ClassName:
    def __init__(self, attribute1, attribute2, ...): 
        self.attribute1 = value1 
        self.attribute2 = value2  

Here, the method name must be __init__().

• The self parameter is always first, and it refers to the instance.
• Other parameters, i.e., attribute1, attribute2,... refer to the object attributes that the method will intialize.
• The values (value1, value2,...) refer to the values assigned to the respective attributes at the time of object creation.

Code Example:

            class Student:
    def __init__(self, name, age):
        self.name = name # Instance attribute
        self.age = age # Instance attribute

    def introduce(self):
        print(f"My name is {self.name}, and I am {self.age} years old.")

# Creating objects
student1 = Student("Amit", 21)
student2 = Student("Priya", 22)

# Calling the introduce() method
student1.introduce()
student2.introduce()
          

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

Output:

My name is Amit, and I am 21 years old.
My name is Priya, and I am 22 years old.

Code Explanation:

We once again define a Student class with an introduce() method, two attributes, and an __init__() method (constructor) that initializes the attribute when an object is created. Let’s see how this works:

• After the class definition, we create two objects of the Student class.
• For student1 we assing values “Amit” and 21 for the name and age attributes (respectively) and for student2 values “Priya” and 22.
• When we use the class name to create the objects, the __init__() method is called automatically. 
• As shown in the method definition, this method assigns the attribute values behind the scenes.
• That is, self.name = name and self.age = age initialize attributes for each object.
• Each object gets its own unique values based on the arguments passed.

What Happens If We Don’t Use __init__()?

Without the __init__() method, we would have to set attributes manually every time an object is created. Here is what object creation would look like (from the example above) if we did not have an __init__() method in the class definition:

student1 = Student()  # No __init__, so attributes are missing
student1.name = "Amit"
student1.age = 21

As is evident, using the __init__() method is more efficient than initializing every single attribute of every single object individually. With __init__(), attributes are automatically initialized, ensuring every object starts with valid data.

Default Values In The __init__() Method Of Python Classes

To avoid passing values manually every time, we can provide default values in __init__(). If no values are passed during object creation, these defaults are automatically assigned. However, if arguments are provided, they override the default values. The sample Python program below illustrates this feature of the method.

Code Example:

            class Student:
    def __init__(self, name="Unknown", age=18):
        self.name = name
        self.age = age
    def introduce(self):
        print(f"My name is {self.name}, and I am {self.age} years old.")

# Creating an object without passing arguments
student1 = Student()
student1.introduce()

# Creating an object with arguments
student2 = Student("Priya", 22)
student2.introduce()
          

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

Output:

My name is Unknown, and I am 18 years old.
My name is Priya, and I am 22 years old.

Code Explanation:

In the __init__() method, the name and age attributes have default values ("Unknown" and 18).

• If an object is created without arguments (student1), these default values are used.
• If an object is created with arguments (student2), the provided values override the defaults.

Why Use Default Values?

• They prevent errors when arguments are missing.
• They provide a fallback option, making the class more flexible and user-friendly.

Quick Question!

The __str__() Method In Python Classes

The __str__() method is a special method in Python that returns a string representation of an object. It is automatically called when you use the built-in functions print() or the str(). Without __str__(), if you use the print() function for displaying an object, it only returns an unreadable memory address, as shown in the example below.

Code Example:

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

# Creating an object
student1 = Student("Amit", 21)

# Printing the object
print(student1)
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lLCBhZ2UpOgogICAgICAgIHNlbGYubmFtZSA9IG5hbWUKICAgICAgc2VsZi5hZ2UgPSBhZ2UKCiMgQ3JlYXRpbmcgYW4gb2JqZWN0CnN0dWRlbnQxID0gU3R1ZGVudCgiQW1pdCIsIDIxKQoKIyBQcmludGluZyB0aGUgb2JqZWN0CnByaW50KHN0dWRlbnQxKQ==

Output: 

<__main__.Student object at 0x7f9a5c5b7cd0>

This isn’t very useful, right? That’s where __str__() comes in! To return a readable representation of the object, define the __str__() method inside the class.

Code Example:

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

    def __str__(self):
      return f"Student(name={self.name}, age={self.age})"

# Creating an object
student1 = Student("Amit", 21)

# Printing the object
print(student1)
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lLCBhZ2UpOgogICAgICAgIHNlbGYubmFtZSA9IG5hbWUKICAgICAgICBzZWxmLmFnZSA9IGFnZQoKICAgIGRlZiBfX3N0cl9fKHNlbGYpOgogICAgICByZXR1cm4gZiJTdHVkZW50KG5hbWU9e3NlbGYubmFtZX0sIGFnZT17c2VsZi5hZ2V9KSIKCiMgQ3JlYXRpbmcgYW4gb2JqZWN0CnN0dWRlbnQxID0gU3R1ZGVudCgiQW1pdCIsIDIxKQoKIyBQcmludGluZyB0aGUgb2JqZWN0CnByaW50KHN0dWRlbnQxKQ==

Output: 

Student(name=Amit, age=21)

Code Explanation:

In the example above, we continue with the Student class, but here, in addition to the __init__() method, we also define another method:

• The __str__() returns a formatted string representing the object.
• When we use the print() function, Python automatically calls the __str__() method, displaying a human-readable output instead of a memory address.

Using str() with __str__() In Classes In Python

As mentioned before, we can invoke the __str__() method by calling either the print() function or the built-in string function str(). Here is a snippet of the example above showing the use of str() instead of print():

student1 = Student("Amit", 21)
# Explicitly calling str()
student_str = str(student1)
print(student_str)  # Output: Student(name=Amit, age=21)

Just like in the case of print(), behind the scenes, str(student1) is the same as student1.__str__().

The Role Of self Parameter In Python Classes

In Python, self is a reference to the current instance of a class. It’s always the first parameter in instance methods, though you don’t explicitly pass it when calling a method.

But why do we need self? Can’t Python just figure it out on its own? Not really.

Why Do We Need self?

Without the self parameter, Python wouldn’t know which object’s data/attributes to access or modify. It serves three key purposes:

1. Accessing instance attributes: Each object (instance) has its own separate data. Using self ensures that methods refer to the correct object’s attributes.
2. Modifying instance attributes: If we want to update an object’s attribute, we must use self, or else Python will think we’re creating a new local variable instead of modifying the instance attribute.
3. Distinguishing instance variables from local variables: Variables inside a method without self are temporary (local to that method) and disappear once the method ends. 

Example: How self Works In A Python Class

            class Student:
    def __init__(self, name, age):
        self.name = name # Assigning instance attributes 
        self.age = age

    def display_info(self):
        print(f"Name: {self.name}, Age: {self.age}") # Accessing instance attributes  

    def update_age(self, new_age):
        self.age = new_age # Modifying an instance attribute  

# Creating an object 
student1 = Student("Amit", 21)

# Accessing attributes 
student1.display_info()

# Modifying an attribute using self 
student1.update_age(22)
student1.display_info()
          

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

Output:

Name: Amit, Age: 21
Name: Amit, Age: 22  

Code Example:

In the example, we define the Student class with an __init__() method, two class attributes (name and age) and two methods (display_info and update_age()).

• Using self in __init__(): The self.name = name and self.age = age assignments ensure the attributes belong to the instance (not just temporary variables).
• Accessing Attributes: The display_info() method prints values using self.name and self.age.
• When we call student1.display_info(), Python automatically passes student1 as self, allowing access to the correct attributes.
• Modifying Attributes: The update_age() method updates the age attribute of student1.
• Calling student1.update_age(22) updates self.age from 21 to 22, which persists for future method calls.

What Happens If We Remove self?

Let’s see what happens if we forget self:

            class Student:
    def __init__(name, age): # ❌ Missing self 
        name.name = name # ❌ Incorrect 
        name.age = age # ❌ Incorrect  
student1 = Student("Amit", 21)
          

Y2xhc3MgU3R1ZGVudDoKICAgIGRlZiBfX2luaXRfXyhuYW1lLCBhZ2UpOiAjIOKdjCBNaXNzaW5nIHNlbGbCoAogICAgICAgIG5hbWUubmFtZSA9IG5hbWUgIyDinYwgSW5jb3JyZWN0wqAKICAgICAgICBuYW1lLmFnZSA9IGFnZSAjIOKdjCBJbmNvcnJlY3TCoMKgCnN0dWRlbnQxID0gU3R1ZGVudCgiQW1pdCIsIDIxKQ==

Output:

TypeError: __init__() missing 1 required positional argument: 'age'

Why does this happen?

• Without self, Python treats name as a regular parameter instead of a reference to the object.
• The assignments name.name = name and name.age = age don’t make sense because name is just a parameter, not an instance.

Key takeaway: The self parameter is essential for storing and accessing instance attributes correctly. Without it, Python treats variables as local to the method instead of belonging to an object.

Check out this amazing course to become the best version of the Python programmer you can be.

Different Methods In Classes In Python

A class method is a function inside a class that operates on the class’s objects. It defines behaviors like:

• Updating/modifying object attributes
• Performing calculations/operations
• Returning useful data

Main Types Of Class Methods In Python

Python has three main types of methods that are used inside a Python class:

Let’s explore each with examples.

Instance Methods In Python Classes

Instance methods work with individual objects (instances). They must include the self parameter, which refers to the specific object calling the method. These are the most commonly used class methods in Python programming.

Code Example:

            class Car:
    def __init__(self, brand, model, year):
        self.brand = brand
        self.model = model
        self.year = year
        self.speed = 0 # Initial speed

    def accelerate(self, amount):
        self.speed += amount
        print(f"{self.brand} {self.model} is now moving at {self.speed} km/h.")

# Creating an object
car1 = Car("Toyota", "Corolla", 2022)

# Calling an instance method
car1.accelerate(20)class Car:
    def __init__(self, brand, model, year):
        self.brand = brand
        self.model = model
        self.year = year
        self.speed = 0 # Initial speed

    def accelerate(self, amount):
        self.speed += amount
        print(f"{self.brand} {self.model} is now moving at {self.speed} km/h.")

# Creating an object
car1 = Car("Toyota", "Corolla", 2022)

# Calling an instance method
car1.accelerate(20)
          

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

Output: 

Toyota Corolla is now moving at 20 km/h.

Code Explanation:

In this example, we have defined one instance method, i.e., accelerate(). 

• When we call the function, accelerate(self, amount), it takes the amount as input and increases the car’s speed by that number.
• Inside the function definition, the expression self.speed += amount, modifies the specific object’s speed.
• Note that the car1.accelerate(20) call updates car1's speed, but not other objects.

Class Methods (Affect The Whole Class)

Class methods work at the class itself and not individual instances/objects of the class.

• We use the expression/decorator @classmethod when defining these method types.
• Instead of the self parameter, these methods take the cls parameter referring to the respective class.
• They operate on class attributes, which apply to all instances.

Code Example:

            class Car:
    wheels = 4 # Class attribute

    @classmethod #Class method
    def change_wheels(cls, new_wheel_count):
        cls.wheels = new_wheel_count

# Changing wheels for all cars
Car.change_wheels(6)
print(Car.wheels)
          

Y2xhc3MgQ2FyOgogICAgd2hlZWxzID0gNCAjIENsYXNzIGF0dHJpYnV0ZQoKICAgIEBjbGFzc21ldGhvZCAjQ2xhc3MgbWV0aG9kCiAgICBkZWYgY2hhbmdlX3doZWVscyhjbHMsIG5ld193aGVlbF9jb3VudCk6CiAgICAgICAgY2xzLndoZWVscyA9IG5ld193aGVlbF9jb3VudAoKIyBDaGFuZ2luZyB3aGVlbHMgZm9yIGFsbCBjYXJzCkNhci5jaGFuZ2Vfd2hlZWxzKDYpCnByaW50KENhci53aGVlbHMp

Output: 

6

Code Explanation:

In this example, wheels is a class attribute shared across all instances.

• The change_wheels() method updates the value of the wheels attribute for all cars, not just one.
• When we call this method, i.e., Car.change_wheels(6), it changes the number of wheels for every car instance.

Static Methods In Python Classes

A static method is a function inside a class that doesn’t modify instance (self) or class (cls) attributes. Instead, it provides a utility function relevant to the class. We define static methods using the @staticmethod decorator. These methods:

• Belong to the class logically but don’t depend on its attributes.
• Cannot access or modify instance (self) or class (cls) attributes.
• They are useful for general calculations or independent operations related to the class.

Code Example:

            class Car:
    def __init__(self, brand, model, fuel_capacity):
        self.brand = brand
        self.model = model
        self.fuel_capacity = fuel_capacity # Fuel capacity in liters

    @staticmethod
    def convert_liters_to_gallons(liters):
        return liters * 0.264172 # Converts liters to gallons

# Using the static method
print(Car.convert_liters_to_gallons(50)) # Convert 50 liters to gallons
          

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

Output:

13.2086

Why is convert_liters_to_gallons a static method?

• The conversion formula logically belongs in the Car class (since it’s fuel-related).
• But it doesn’t depend on any car’s attributes as it just takes an input (liters) and returns a value.
• It can be called using Car.convert_liters_to_gallons(50) without needing an object.

Instance Attributes vs. Class Attributes In Python Classes

Attributes in Python classes store data about objects. But not all attributes behave the same way. There are two types of attributes:

• Instance attributes belong to individual objects.
• Class attributes are shared across all objects of a class.

Think of it like this:

• Every student has their own name and roll number (instance attributes).
• But all students belong to the same school (class attribute).

Instance Vs. Class Attributes: Key Differences

The table below highlights the key difference between the two attributes of classes in Python. It is important to understand this to make the correct of classes as a concept.

Example: Instance Vs. Class Attributes In Action

            class Student:
    school = "Greenwood High"  # Class attribute (shared)
    def __init__(self, name):
        self.name = name  # Instance attribute (unique)
# Creating two student objects
s1 = Student("Jeet")
s2 = Student("Jhanvi")

# Accessing instance attributes
print(s1.name) # Output: Jeet
print(s2.name) # Output: Jhanvi

# Accessing class attribute
print(s1.school) # Output: Greenwood High
print(s2.school) # Output: Greenwood High

# Modifying instance attribute (affects only s1)
s1.name = "Chirag"
print(s1.name) # Output: Chirag
print(s2.name) # Output: Jhanvi (unchanged)

# Modifying class attribute (affects all instances)
Student.school = "Blue Ridge School"
print(s1.school) # Output: Blue Ridge School
print(s2.school) # Output: Blue Ridge School
          

Y2xhc3MgU3R1ZGVudDoKwqAgwqAgc2Nob29sID0gIkdyZWVud29vZCBIaWdoIsKgICMgQ2xhc3MgYXR0cmlidXRlIChzaGFyZWQpCsKgIMKgIGRlZiBfX2luaXRfXyhzZWxmLCBuYW1lKToKwqAgwqAgwqAgwqAgc2VsZi5uYW1lID0gbmFtZcKgICMgSW5zdGFuY2UgYXR0cmlidXRlICh1bmlxdWUpCiMgQ3JlYXRpbmcgdHdvIHN0dWRlbnQgb2JqZWN0cwpzMSA9IFN0dWRlbnQoIkplZXQiKQpzMiA9IFN0dWRlbnQoIkpoYW52aSIpCgojIEFjY2Vzc2luZyBpbnN0YW5jZSBhdHRyaWJ1dGVzCnByaW50KHMxLm5hbWUpICMgT3V0cHV0OiBKZWV0CnByaW50KHMyLm5hbWUpICMgT3V0cHV0OiBKaGFudmkKCiMgQWNjZXNzaW5nIGNsYXNzIGF0dHJpYnV0ZQpwcmludChzMS5zY2hvb2wpICMgT3V0cHV0OiBHcmVlbndvb2QgSGlnaApwcmludChzMi5zY2hvb2wpICMgT3V0cHV0OiBHcmVlbndvb2QgSGlnaAoKIyBNb2RpZnlpbmcgaW5zdGFuY2UgYXR0cmlidXRlIChhZmZlY3RzIG9ubHkgczEpCnMxLm5hbWUgPSAiQ2hpcmFnIgpwcmludChzMS5uYW1lKSAjIE91dHB1dDogQ2hpcmFnCnByaW50KHMyLm5hbWUpICMgT3V0cHV0OiBKaGFudmkgKHVuY2hhbmdlZCkKCiMgTW9kaWZ5aW5nIGNsYXNzIGF0dHJpYnV0ZSAoYWZmZWN0cyBhbGwgaW5zdGFuY2VzKQpTdHVkZW50LnNjaG9vbCA9ICJCbHVlIFJpZGdlIFNjaG9vbCIKcHJpbnQoczEuc2Nob29sKSAjIE91dHB1dDogQmx1ZSBSaWRnZSBTY2hvb2wKcHJpbnQoczIuc2Nob29sKSAjIE91dHB1dDogQmx1ZSBSaWRnZSBTY2hvb2w=

Key Takeaways

1. Instance attributes (name) → Different for each student.
2. Class attribute (school) → Same for all students.
3. Changing an instance attribute affects only that object.
4. Changing a class attribute affects all instances.

Quick Question!

Object-Oriented Programming (OOP) Concepts In Python

Python follows the Object-Oriented Programming (OOP) paradigm, making code modular, reusable, and scalable. The four key OOP principles are:

1. Encapsulation: Bundles data and methods inside a class while restricting direct access to internal data.

• Instance variables & methods keep data within objects.
• Private attributes (__attribute) prevent external modification.
• Example: A Student class stores details, but marks (__marks) remain private.

2. Inheritance: Enables a new class (child) to inherit properties and methods from an existing class (parent).

• The child class automatically gets all attributes and methods from the parent.
• Objects of the child class can access both inherited and new attributes/methods.
• Example: A Car class is inherited by ElectricCar, reusing attributes like wheels.

3. Polymorphism: Allows the same method to behave differently based on the object.

• Different classes can define a common method that behaves uniquely.
• Achieved through method overriding (child class redefines parent method) and method overloading (same method, different parameters).
• Example: A speak() method behaves differently for Dog (Bark!) and Cat (Meow!).

4. Abstraction: Hides complex details and exposes only essential functionalities.

• Implemented using abstract classes (ABC Python module).
• Ensures objects can only call essential methods, keeping implementation hidden.
• Example: A Vehicle class defines move(), but Car and Bike implement it differently.

Looking for guidance? Find the perfect mentor from select experienced coding & software development experts here.

Practical Examples Of Classes & Objects In Python

Classes and objects form the foundation of Python programming, making code modular, reusable, and efficient. Let's look at three real-world use cases where classes help structure programs.

Student Management System 📚

Every university needs a system to store student records. Using a class, we can create student objects with attributes like name, roll number, and marks. This makes it easier to organize, access, and modify the information as needed.

Code Example:

            class Student:
    def __init__(self, name, roll_no, marks):
        self.name = name
        self.roll_no = roll_no
        self.marks = marks

    def display_info(self):
      print(f"Student: {self.name}, Roll No: {self.roll_no}, Marks: {self.marks}")

# Creating student objects
student1 = Student("Aarav", 101, 92)
student2 = Student("Ishita", 102, 88)

# Display student details
student1.display_info()
student2.display_info()
          

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

Output:

Student: Aarav, Roll No: 101, Marks: 92
Student: Ishita, Roll No: 102, Marks: 88

Code Explanation:

• We define a Student class with __init__() to initialize name, roll number, and marks.
• The display_info() method prints student details.
• We create two student objects and call display_info().

This approach makes it easy to manage multiple student records efficiently!

E-commerce Product Catalog 🛒

E-commerce platforms need to handle multiple products, each with different prices and stock. We can create a Product class to manage product details.

Code Example:

            class Product:
    def __init__(self, name, price, stock):
        self.name = name
        self.price = price
        self.stock = stock

    def purchase(self, quantity):
        if quantity <= self.stock:
            self.stock -= quantity
            print(f"Purchased {quantity} {self.name}(s). Remaining stock: {self.stock}")
        else:
            print("Not enough stock available.")

# Creating product objects
laptop = Product("Laptop", 60000, 10)
phone = Product("Smartphone", 25000, 5)

# Purchasing products
laptop.purchase(2)
phone.purchase(6)
          

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

Output:

Purchased 2 Laptop(s). Remaining stock: 8
Not enough stock available.

Code Explanation:

We create the Product class to store information about any product. Every single product can have attributes: name, price, stock/quantity.

• The purchase() method reduces stock when an item is bought.
• If the stock is insufficient, an error message is shown.

This structure is scalable and forms the base of real e-commerce systems!

Banking System (Account Management) 💰

Banks manage multiple customer accounts with features like deposits and withdrawals. We can model this using classes.

Code Example:

            class BankAccount:
    def __init__(self, account_holder, balance=0):
        self.account_holder = account_holder
        self.balance = balance

    def deposit(self, amount):
        self.balance += amount
        print(f"Deposited ₹{amount}. New Balance: ₹{self.balance}")

    def withdraw(self, amount):
        if amount <= self.balance:
            self.balance -= amount
            print(f"Withdrew ₹{amount}. Remaining Balance: ₹{self.balance}")
        else:
            print("Insufficient funds.")

# Creating bank account objects
account1 = BankAccount("Rohan", 5000)
account2 = BankAccount("Simran", 10000)

# Transactions
account1.deposit(2000)
account1.withdraw(3000)
account2.withdraw(12000)
          

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

Output:

Deposited ₹2000. New Balance: ₹7000
Withdrew ₹3000. Remaining Balance: ₹4000
Insufficient funds.

Code Explanation:

• The BankAccount class stores account details.
• The deposit() method increases the balance.
• The withdraw() method checks if funds are available before withdrawing.

This is a simplified version of real banking systems, making transactions secure and manageable!

Why & When To Use Classes In Python Programs?

Python offers multiple ways to structure code—functions, lists, dictionaries, and classes. While functions work well for small scripts, classes become essential when dealing with complex, reusable, and scalable code.

Let’s break it down!

Why Use Classes In Python?

Classes provide:

• Code Organization & Reusability: Encapsulating data and behavior in a class makes the code modular and reusable.
• Scalability: Large projects benefit from structured classes rather than scattered functions.
• Encapsulation: Data hiding and restricting direct access to attributes make code more secure.
• DRY Principle (Don’t Repeat Yourself): Reduces redundancy by defining a class once and creating multiple objects from it.
• Flexibility: Objects can be dynamically modified without affecting other instances.

When Should You Use Classes?

Use classes when:

• Multiple entities share similar properties & behavior. Example: A Student class instead of storing details in separate dictionaries.
• You need to model real-world objects. Example: Cars, employees, bank accounts, products, etc.
• Your program requires state persistence. Example: Keeping track of users logged into a system.
• Data and related operations need to be grouped together. Example: An Invoice class that holds both customer details and billing calculations.
• You need inheritance & polymorphism for code extension. Example: A Vehicle class with subclasses like Car, Bike, and Truck.

When Not To Use Classes?

If the code is simple and doesn’t require object management, using functions or dictionaries might be better. For instance, if you just need to add two numbers, defining a Calculator class is overkill!

Ready to upskill your Python game? Dive deeper into actual problem statements and elevate your coding game with hands-on practice!

Common Pitfalls Of Using Classes In Python Programs

While classes in Python make code modular and reusable, poor design choices can lead to unnecessary complexity and inefficiencies. Here are some common pitfalls to avoid:

1. Overcomplicating Simple Problems: Using classes when simple functions or data structures (like dictionaries) would suffice.
   Fix: Use classes only when state management, encapsulation, or reusability is needed.
2. Misusing the self Parameter: Forgetting self in instance methods, leading to unbound method errors.
   Fix: Always use self to access instance attributes inside methods.
3. Not Using the init() Method Properly: Forgetting to initialize attributes in __init__() and assigning them later.
   Fix: Define all necessary attributes inside __init__() to ensure proper object initialization.
4. Using Class Attributes Instead of Instance Attributes: Accidentally defining attributes at the class level, causing all instances to share the same data.
   Fix: Use self.attribute_name inside __init__() to create unique attributes for each instance.
5. Creating Large, Monolithic Classes: Packing too much functionality into a single class, making it hard to maintain.
   Fix: Follow the Single Responsibility Principle (SRP)—each class should have one clear purpose.
6. Ignoring Encapsulation & Making Everything Public: Directly modifying object attributes from outside the class.
   Fix: Use getter and setter methods or name attributes with a single underscore _attribute (protected) or double underscores __attribute (private).
7. Forgetting to Use Special Methods (__str__(), __repr__()): Printing objects gives unreadable output (e.g., <__main__.Car object at 0x000002>).
   Fix: Implement __str__() to return a meaningful string representation of the object.

Conclusion

Classes and objects are fundamental to Python’s object-oriented programming (OOP) paradigm, allowing for structured, reusable, and scalable code. 

• A class serves as a blueprint, while an object is an instance of that blueprint with unique attributes and behaviors. 
• Using methods, including special methods like __init__() and __str__(), we can define how objects are initialized, modified, and represented.
• Understanding instance vs. class attributes, encapsulation, and method types is crucial for effective class design. 

While Python classes add modularity and organization, overuse or poor structuring can lead to unnecessary complexity. By following best practices, you can write cleaner, more maintainable Python programs, whether for small scripts or large-scale applications.

Frequently Asked Questions

Q1. What is the difference between a class and an object in Python?

A class is a blueprint for creating objects, while an object is an instance of a class with its own unique attributes and behaviors.

Q2. Can a class exist without objects?

Yes! A class can exist without any objects, but it serves no practical purpose unless instantiated.

Q3. What happens if you don’t define an __init__() method?

Python will create objects with default attributes, but you’ll need to assign values manually. The __init__() method helps initialize objects automatically.

Q4. Is self a keyword in Python?

No, self is just a naming convention for referring to the instance of a class. You can rename it, but using self is standard practice.

Q5. What is the difference between __str__() and __repr__()?

• __str__() returns a user-friendly string representation of an object.
• __repr__() returns a detailed, developer-friendly representation for debugging.

Q6. When should I use instance attributes vs. class attributes?

• Use instance attributes when each object needs its own unique values.
• Use class attributes when all instances should share the same value (e.g., a constant).

Q7. Can We Change self to Something Else?

Technically, yes! The self is not a keyword, but just a parameter placeholder or a convention. You could rename it, as shown in the example below:

class Student:
    def __init__(this, name, age):  # Works, but avoid!
        this.name = name
        this.age = age
    def display_info(this):
        print(f"Name: {this.name}, Age: {this.age}")

Here, we use the word ‘this’ to fulfil the role of the self parameter. While it works, it’s unnecessary and makes your code less readable. It is better to stick to the convection when working with classes in Python programs.

You must also read the following:

• Python input() Function (+Input Casting & Handling With Examples)
• Python Libraries | Standard, Third-Party & More (Lists + Examples)
• Python Program To Convert Decimal To Binary, Octal And Hexadecimal
• Fix Indexerror (List Index Out Of Range) In Python +Code Examples
• Python Program To Convert Kilometers To Miles (+Detailed Examples)