Inheritance & Method Overriding0%
Polymorphism Basics

Inheritance & Method Overriding

Beginner12 min read•Updated: Jul 11, 2026
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Inheritance & Method Overriding in Python

Inheritance is a cornerstone of Object-Oriented Programming that enables a child (derived) class to inherit attributes and methods from a parent (base) class. It facilitates clean code reuse, models hierarchical domain relationships ("is-a"), and allows subclasses to specialize or override behaviors.

1. Single Inheritance Basics

In Python, inheritance is declared by passing the parent class name inside parentheses after the child class definition:

Python
class Vehicle:
def __init__(self, brand: str, model: str):
self.brand = brand
self.model = model
self.speed = 0
 
def accelerate(self, increment: int):
self.speed += increment
print(f"{self.brand} {self.model} accelerated to {self.speed} km/h.")
 
def brake(self):
self.speed = 0
print(f"{self.brand} {self.model} brought to a stop.")
 
# Car inherits all attributes and methods from Vehicle
class Car(Vehicle):
pass
 
my_car = Car("Tata", "Nexon")
my_car.accelerate(50) # Tata Nexon accelerated to 50 km/h.
my_car.brake() # Tata Nexon brought to a stop.

2. Extending Constructors with super().__init__()

When a child class needs its own unique attributes in addition to those of the parent, use the built-in super() function to invoke the parent class's constructor:

Python
class Vehicle:
def __init__(self, brand: str, model: str, year: int):
self.brand = brand
self.model = model
self.year = year
 
class ElectricCar(Vehicle):
def __init__(self, brand: str, model: str, year: int, battery_kwh: float):
# 1. Delegate core vehicle initialization to the parent class
super().__init__(brand, model, year)
# 2. Initialize subclass-specific attribute
self.battery_kwh = battery_kwh
self.charge_percent = 100
 
def charge(self):
self.charge_percent = 100
print(f"{self.brand} {self.model} battery charged to 100%.")
 
ev = ElectricCar("Tata", "Punch EV", 2024, 35.0)
print(f"Vehicle: {ev.brand} {ev.model} ({ev.year}) | Battery: {ev.battery_kwh} kWh")
ev.charge()

3. Method Overriding

Method Overriding occurs when a child class provides a custom implementation of a method that is already defined in its parent class.

Full Override vs. Cooperative Augmentation

  1. 1
    Full Override: The child method completely replaces the parent method logic.
  2. 2
    Augmentation: The child method runs custom logic before or after calling super().method_name().
Python
class Employee:
def __init__(self, name: str, base_salary: float):
self.name = name
self.base_salary = base_salary
 
def calculate_annual_pay(self) -> float:
return self.base_salary * 12
 
def display_role(self):
print(f"{self.name} is a standard corporate employee.")
 
 
class Manager(Employee):
def __init__(self, name: str, base_salary: float, quarterly_bonus: float):
super().__init__(name, base_salary)
self.quarterly_bonus = quarterly_bonus
 
# Method Overriding with Augmentation using super()
def calculate_annual_pay(self) -> float:
standard_pay = super().calculate_annual_pay()
total_bonuses = self.quarterly_bonus * 4
return standard_pay + total_bonuses
 
# Complete Method Override
def display_role(self):
print(f"{self.name} is an Engineering Manager leading a team.")
 
emp = Employee("Ramesh", 50000)
mgr = Manager("Sneha", 90000, 15000)
 
print(f"{emp.name} Annual Pay: ₹{emp.calculate_annual_pay():,.2f}") # ₹600,000.00
print(f"{mgr.name} Annual Pay: ₹{mgr.calculate_annual_pay():,.2f}") # ₹1,140,000.00
 
emp.display_role()
mgr.display_role()

4. Multiple Inheritance & Method Resolution Order (MRO)

Python supports multiple inheritance, where a class inherits from two or more parent classes. The order in which methods are resolved is dictated by the C3 Linearization algorithm, accessible via the mro() method or __mro__ attribute.

Python
class Device:
def ping(self):
print("Device responding.")
 
class WiFiEnabled(Device):
def ping(self):
print("WiFi Ping: Connected to router.")
 
class BluetoothEnabled(Device):
def ping(self):
print("Bluetooth Ping: Connected to paired unit.")
 
# Multiple inheritance order determines resolution
class SmartSpeaker(WiFiEnabled, BluetoothEnabled):
pass
 
speaker = SmartSpeaker()
speaker.ping() # Output: WiFi Ping: Connected to router.
 
# Inspect the MRO path
print([cls.__name__ for cls in SmartSpeaker.__mro__])
# ['SmartSpeaker', 'WiFiEnabled', 'BluetoothEnabled', 'Device', 'object']

5. Type Introspection: isinstance() vs. issubclass()

Always use Python's built-in inspection functions rather than comparing raw type(obj) == Class:

Python
ev = ElectricCar("Tesla", "Model 3", 2023, 75.0)
 
# Check instance relationship
print(isinstance(ev, ElectricCar)) # True
print(isinstance(ev, Vehicle)) # True (inherited)
print(isinstance(ev, object)) # True (root of all Python objects)
 
# Check class hierarchy relationship
print(issubclass(ElectricCar, Vehicle)) # True
print(issubclass(Vehicle, ElectricCar)) # False

Multiple Choice Questions

1. Which function is used in a child class constructor to call the parent class's __init__ method?

A. parent().__init__() B. super().__init__() C. this.__init__() D. base().__init__() Answer: B Explanation: super() returns a proxy object that delegates method calls to the parent or sibling classes according to the class MRO.

2. What happens when a child class defines a method with the exact same name and signature as its parent class?

A. A NameConflictError is raised at compilation B. The child class method overrides the parent class method C. Both methods are merged together automatically D. Python ignores the child method and defaults to the parent Answer: B Explanation: Defining a method in a child class with the same name as a parent method overrides the parent implementation when invoked on instances of the child.

3. What does MRO stand for in Python's object model?

A. Method Return Object B. Main Runtime Order C. Method Resolution Order D. Memory Reference Optimization Answer: C Explanation: MRO stands for Method Resolution Order, the deterministic order in which Python searches class hierarchies for attributes and methods.

4. Which built-in function checks whether a specific class inherits from another class?

A. isinstance() B. issubclass() C. hasattr() D. isderived() Answer: B Explanation: issubclass(sub, sup) returns True if sub is a direct or indirect subclass of sup.

5. If class Dog(Animal) does not define its own __init__ method, what constructor is executed when running Dog()?

A. Python creates a dummy object without initializing attributes B. The constructor of Animal is automatically called C. A TypeError is raised because constructors are mandatory D. The __init__ method of type is called Answer: B Explanation: If a child class does not declare an __init__ method, Python traverses the MRO and calls the parent's __init__ method automatically.

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