Subclasses in Python

In Python, a subclass (also known as a derived class) is a class that extends another class, referred to as the base or parent class.

class SubclassName(BaseClass):
code

What’s the purpose of a subclass?

The key benefit of using subclasses is inheritance.

A subclass inherits all the properties of its base class, allowing you to avoid redundant code and streamline your programming.

A Practical Example of a Subclass

To illustrate how subclasses work in Python, let’s walk through a simple example.

First, I'll create a base class A() with a single property.

1. class A:
2. country = "Italy"

Next, I'll define a derived class B(A).

This subclass adds a new property (region).

1. class B(A):
2. region = "Lazio"

By specifying the base class (A) in parentheses, we indicate that class B automatically inherits all the properties of the base class A.

For example, if I enter the following in the Python interpreter:

B.country

The interpreter retrieves the property from B and outputs:

Italy

Even though the subclass B doesn’t explicitly define this property, it inherits the "country" property from the base class A.

And so forth.

How to Create a Derived Class

This next example is a bit more advanced because it includes methods, but the underlying concept remains consistent.

First, I'll create a base class Person().

Objects belonging to the Person() class have two properties: first name and last name.

1. class Person():
2. '''Class that represents a person.'''
3. def __init__(self, first_name, last_name):
4. self.first_name = first_name
5. self.last_name = last_name
6. def __str__(self):
7. return "First Name: " + str(self.first_name) + "\nLast Name: " + str(self.last_name)

Next, I'll create a subclass called Student().

The base class, in this case, is specified in parentheses as Person.

1. class Student(Person):
2. '''Class that represents a student.'''
3. def __init__(self, first_name, last_name, school):
4. self.school = school
5. Person.__init__(self, first_name, last_name)
6. def __str__(self):
7. return Person.__str__(self) + "\nSchool: " + str(self.school)

The Student subclass introduces a specific property (school) while inheriting the first_name and last_name properties from the base class Person.

To test this, I'll create an instance of the Student() class:

eric = Student("Eric", "Idle", "British School")

Now, I'll inspect the eric object:

eric

The Python interpreter returns the following information:

First Name: Eric
Last Name: Idle
School: British School

The Student() subclass has inherited the methods of the base class Person().

And so on.