Python Inheritance

What Is Inheritance?

Inheritance lets one class reuse behavior from another class. The existing class is often called the parent class or base class. The new class is called the child class or subclass.

class Animal:
    def speak(self):
        return "Some sound"

class Dog(Animal):
    pass

Dog inherits the speak() method from Animal.

Creating A Child Class

Put the parent class name in parentheses.

class ElectricCar(Car):
    pass

The child class can use methods and attributes defined in the parent, as long as normal access rules allow it.

Method Overriding

A child class can replace a parent method by defining a method with the same name.

class Dog(Animal):
    def speak(self):
        return "Bark"

Now Dog().speak() returns "Bark" instead of "Some sound".

Using super()

Use super() to call behavior from the parent class.

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

This lets the parent class initialize its part of the object before the child adds more details.

Is-A Relationship

Inheritance works best when the child class is a more specific kind of the parent class. A Dog is an Animal. An ElectricCar is a Car.

If the relationship is only “uses” or “has”, composition may be clearer than inheritance. For example, a Car has an Engine, but a Car is not an Engine.

Common Mistakes

A common mistake is using inheritance only to share a few helper functions. If the classes do not form an is-a relationship, a separate function or composed object may be simpler.

Another mistake is forgetting to call super().__init__() when the parent initialization is still needed. This can leave required parent attributes unset.

Quick Summary

• Inheritance lets a child class reuse parent class behavior.
• The parent class goes in parentheses after the child class name.
• A child class can override parent methods.
• super() calls parent class behavior.
• Use inheritance when there is a true is-a relationship.
• Prefer simpler composition when classes do not naturally inherit.

Practice Quiz

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