Python OOP Fundamentals: Classes, Objects, Inheritance, and Constructors Explained

Python Object‑Oriented Programming (OOP)

Python’s OOP model lets developers model real‑world entities as objects defined by classes. The language prioritises code reuse and modularity, making it straightforward to create and extend classes.

What Is a Class?

A class is a logical container that bundles data (attributes) and behaviour (methods). It defines a template for objects that share common properties.

Example: A Customer class could expose attributes such as transactions, balance, and debt, along with methods to deposit() or withdraw().

Defining a Class in Python

Follow these steps to create a simple class:

1. Use the class keyword:

   class MyClass:
       pass

2. Define methods inside the class. The first parameter of every instance method is self, which refers to the object itself.

   class MyClass:
       def greet(self):
           print("Hello from MyClass")

3. Instantiate the class:

   obj = MyClass()

4. Call its methods:

   obj.greet()

Complete example:

# Working example of a Python class
class MyClass:
    def method1(self):
        print("Guru99")
    def method2(self, text):
        print("Software Testing: " + text)


def main():
    c = MyClass()
    c.method1()
    c.method2(" Testing is fun")

if __name__ == "__main__":
    main()

Inheritance in Python

Inheritance allows a derived class to reuse and extend the behaviour of a base class. Python supports both single and multiple inheritance.

class Base:
    def greet(self):
        print("Hello from Base")

class Derived(Base):
    def greet(self):
        super().greet()
        print("Hello from Derived")

# Usage
obj = Derived()
obj.greet()

Key points:

• Derived classes inherit attributes and methods automatically.
• Override methods by defining a method with the same name in the subclass.
• Call a parent method explicitly with ParentClass.method(self, …) or super().method().

Constructors: __init__

The __init__ method initializes new objects with predefined values.

class User:
    def __init__(self, name):
        self.name = name
    def say_hello(self):
        print(f"Welcome to Guru99, {self.name}")

user = User("Alex")
user.say_hello()

Output: Welcome to Guru99, Alex

Python 2 vs Python 3

Only minor syntax differences exist. The example above works in both versions with appropriate print statements.

Key Takeaways

• Classes bundle data and behaviour, defined with the class keyword.
• Instance methods use self to refer to the object.
• Inheritance promotes code reuse and can be single or multiple.
• Constructors (__init__) set initial state for new objects.
• Python’s flexible syntax and runtime handling of self make OOP intuitive.