Inheritance

Concept

A mechanism to create a new class (subclasses) that inherits attributes and methods from an existing class (parent classes). It allows for code reuse and establishes a relationship between classes.

Type of Inheritance	Description	Example
Single Inheritance	A subclass inherits from one parent class.	`class Dog(Animal): pass`
Multiple Inheritance	A subclass inherits from multiple parent classes.	`class FlyingDog(Dog, Bird): pass`
Multilevel Inheritance	A subclass inherits from a parent class, which in turn inherits from another parent class.	`Animal -> Mammal -> Dog`
Hierarchical Inheritance	Multiple subclasses inherit from a single parent class.	`Animal -> Dog, Cat, Bird`
Hybrid Inheritance	A combination of two or more types of inheritance.	`class FlyingDog(Dog, Bird): pass` where `Dog` and `Bird` are subclasses of `Animal`.

Implementation

Single Inheritance

animal.py


class Animal:
  def __init__(self, name, age):
    self.name = name
    self.age = age
 
  def speak(self):
    print("Animal speaks")
 
class Dog(Animal):
  def __init__(self, name, age):
    super().__init__(name, age)  # Call the parent class constructor
 
  def speak(self): # method overriding
    print("Woof!")
 
dog = Dog("Buddy", 3)
dog.speak()  # Output: Woof!
print(dog.name)  # Output: Buddy
print(dog.age)   # Output: 3
print(isinstance(dog, Animal))  # Output: True

super().__init__(name, age) is used to call the constructor of the parent class (Animal) to initialize the inherited attributes.
isinstance(dog, Animal) checks if dog is an instance of the Animal class or its subclasses.

Multiple Inheritance

When a class inherits from multiple parent classes, the order is determined by the Method Resolution Order (MRO), which follows the C3 linearization algorithm. This ensures a consistent order of method resolution. The MRO can be checked using the __mro__ attribute or the mro() method. The MRO is a depth-first, left-to-right traversal of the class hierarchy.

animal.py


class Dog:
  def bark(self):
    print("Woof!")
 
class Bird:
  def fly(self):
    print("Bird flies")
 
class FlyingDog(Dog, Bird):
  pass
 
fd = FlyingDog()
fd.bark()  # Output: Woof!
fd.fly()   # Output: Bird flies

The MRO for this is FlyingDog -> Dog -> Bird

Multilevel Inheritance

animal.py


class Animal:
  def eat(self):
    print("Animal eats")
 
class Mammal(Animal):
  pass
 
class Dog(Mammal):
  pass
 
dog = Dog()
dog.eat()  # Output: Animal eats

Hierarchical Inheritance

animal.py


class Animal:
  def sleep(self):
    print("Animal sleeps")
 
class Dog(Animal):
  pass
 
class Cat(Animal):
  pass
 
dog = Dog()
cat = Cat()
dog.sleep()  # Output: Animal sleeps
cat.sleep()  # Output: Animal sleeps

Hybrid Inheritance

animal.py


class Animal:
  def move(self):
    print("Animal moves")
 
class Dog(Animal):
  def bark(self):
    print("Woof!")
 
class Bird(Animal):
  def fly(self):
    print("Bird flies")
 
class FlyingDog(Dog, Bird):
  pass
 
fd = FlyingDog()
fd.move()  # Output: Animal moves
fd.bark()  # Output: Woof!
fd.fly()   # Output: Bird flies