Object Oriented Programming

Object-oriented programming (OOP) is a programming paradigm that revolves around the concept of "objects". Python, C++, Java and many other programming languages are all object-oriented programming languages.

Firstly, let's delve into the key components of OOP.

Class

A class is a blueprint that defines attributes (data) and methods (functions) common to all objects of that class.

For example, if you want to make a toy car, you'd start with a blueprint that tells you what the car should look like and what it should be able to do. In programming, a class is like that blueprint. It defines the properties (characteristics) and behaviors (actions) that objects made from that class will have.

Create a Class

To define a class, use the class keyword followed by the class name. The class name should start with a capital letter.

Example

Create a class named Person, with a property named classification:

# Define a classclass Person:    # Define a class property named "classification"    classification = 'mammals'

In this example, A class named Person is created. Inside the class, a class attribute¹ named classification is defined and initialized with the value mammals. class attributes¹ are attributes shared by all instances of the class.

Now we can use the Person class to initialize objects.

Object

An objet is an instance or example created from a blueprint (class) with its own specifications.

For example, you use a blueprint (class) for car manufacturing to create a toy car (object). The finished toy car that you can hold in your hand is like an object. So, while the class describes what the car should be like, the object is the actual car you can play with.

Create an Object

Example

Create an object "p1" from the Person class. The "p1" object automatically inherits the class attribute classification.

This step is called instantiation.

# Create an instance of the Person class # and assign it to the variable p1p1 = Person()print (p1.classification)

Output:

mammals

The object p1 is an instance of the Person class. Consequently, p1 possesses the class attributes defined within the Person class, such as the classification of being mammals.

The `init()` Function

The examples above are the most basic representations of classes and objects, not typically practical for real-world applications.

For instance, in addition to the common classification of mammals inherited from the class Person, it would be advantageous for the p1 object to possess distinctive attributes such as hobbies and age. To achieve that, the built-in __init__() function is used to initialize newly created instances with specific initial state and attributes.

The __init__() function is a constructor method, that is automatically called when a new instance of a class is created. Its primary purpose is to initialize attributes of the newly created object.

Create a Class with `init()` Function

Add __init__() function to the Person class.

class Person:    classification = 'mammals'    def __init__(self, name, age, hobby):        self.name = name        self.age = age        self.hobby = hobby

Explanation

classification = 'mammals': classification is a class attribute that can be shared among all instances of the Person class.
def __init__()(self, name, age, hobby): This line defines the __init__() function.
- self: The self parameter refers to instances or objects of the class. It's like a placeholer for new objects.
- The parameters name, age, and hobby are function parameters used to receive data needed for creating new instances.
self.name = name: this assigns the argument name (the second name of the code) to the name (the first name of the code) attribute of objects.
self.age = age: this assigns the argument age (the second age of the code) to the age (the first age of the code) attribute of objects.
self.hobby = hobby: this assigns the argument hobby (the second hobby of the code) to the hobby (the first hobby of the code) attribute of objects.

Create instances from the Person class

Create two instances, p1 and p2.

# Create an instance "p1" of the Person class# Pass values to name, age and hobby parametersp1 = Person(name="Alice", age=24, hobby='hiking')
print(p1.name)print(p1.age)print(p1.hobby)
print(p1.classification)

Output:

Alice 24 hiking mammals

When creating p1, the values for name, age, and hobby are provided as keyword arguments to the Person class constructor. These arguments are then assigned to the corresponding attributes of the p1 object using the lines within the class definition: self.name = name, self.age = age, self.hobby = hobby. Therefore, the p1 object obtains attributes: name of "Alice", age of "24", hobby of "hiking".

# Create another instance "p2" of the Person class# Pass different values to name, age and hobby parametersp2 = Person("Jason", 28, 'soccer')
print(p2.name)print(p2.age)print(p2.hobby)
print(p2.classification)

Output:

Jason 28 soccer mammals

Similarly, p2 obtains its own attributes during instantiation: name of "Jason", age of "28", hobby of "soccer".

Both p1 and p2 share the same classification of mammals, since the classification attribute is a class attribute¹ common to all new instances. Attributes defined in the __init__() function are instance attributes² which can vary for different instances.

Annotation

1. Class attributes are defined at the class level (outside of any method, typically near the top of the class definition).

2. Instance attributes are defined in the __init__() method or other methods.

< Previous

Next >

Amazing eBook to learn ggplot2 FAST & EASY

book cover for sliding your way to ggplot2 mastery

Object Oriented Programming

Class

Create a Class

Object

Create an Object

The __init__() Function

Create a Class with __init__() Function

Amazing eBook to learn ggplot2 FAST & EASY

The `init()` Function

Create a Class with `init()` Function