A Simple Example of Python Objects and Classes [+Video]

In Python, everything is an object. Even integers are objects — this is different from programming languages like Java where integers, floats, and Booleans are primitive data types. In this way, Python is built on a rigorously consistent object-oriented paradigm.

Considering that objects are everywhere in Python, object-oriented programming is not well studied by Python coders. A huge mistake! Fortunately, you can fix this by example about of Python objects and classes.

If you manage to read over the whole tutorial, you’ll get rewarded with a PDF cheat sheet about classes and objects. So, stay with me! ?‍♂️

Full Example Code

Here’s a simple example of object orientation in Python. We create two classes Muggle and Wizard, and create multiple instances such as Vernon and Petunia (Muggles), as well as Tom (Wizard). Go ahead and skim over the example, I’ll explain it to you in a moment:

class Muggle:
    def __init__(self, age, name, liking_person):
        self.age = age
        self.name = name
        self.likes = liking_person


class Wizard:
    def __init__(self, age, name):
        self.age = age
        self.name = name
        self.mana = 100

    def like_me(self, victim):
        if self.mana >= 100:
            victim.likes = self.name
            self.mana = self.mana - 100

            
Vernon = Muggle(52, "Vernon",  None)
Petunia = Muggle(49, "Petunia", Vernon)
Vernon.likes = "Petunia"
print(Vernon.likes)


Wiz = Wizard(42, "Tom")
Wiz.like_me(Petunia)
Wiz.like_me(Vernon)
print(Petunia.likes=="Tom" and Vernon.likes=="Tom")

As you go over this tutorial, you can watch me explain it in the following video.

[Video] Python Classes Objects Example from Harry Potter

Python Classes Objects (Harry Potter Example)

Classes Example Explained

You may ask: what is a class anyway?

Classes are “blueprints” for creating objects. A class description tells you everything an object consists of and is able to do (data and functionality).

Today, we are seeing these two concepts in action (with the usual Harry Potter examples):

class Muggle:
    def __init__(self, age, name, liking_person):
        self.age = age
        self.name = name
        self.likes = liking_person


Vernon = Muggle(52, "Vernon",  None)
Petunia = Muggle(49, "Petunia", Vernon)

From this code snippet, you can learn several things:

1. We create a new class “blueprint” for Muggles by using the keyword class. It is an abstract concept — and it shows how every Muggle in our microcosm looks like.
2. We use the “constructor” method __init__(...) to initialize the class with data. In our case, every Muggle has attributes age, name, and likes (a person they like). The first value of any class method (including the constructor) is a reference to the object itself. Remember the class describes the functionality and properties of concrete objects. As soon as you call the constructor in your code, Python creates an empty object which you can access using the name self.

Note that although the first argument is self when defining a method, you don’t actually specify this argument when calling the method. Python internally does it for you. This is just a piece of syntax that you have to remember.

The constructor is a special method of the Muggle class: it allows you to initiate a new object by using the name of the class as a function call. For example, the calls Muggle(52, "Vernon", None) and Muggle(49, "Petunia", Vernon) creates two new class objects both defining the three variables as follows:

You can see that these objects follow the same blueprint but are different instances of the class Muggle. The same type of properties but different DNA.

From now on, these objects live in your computer’s memory until Python garbage collects them.

Can you see the tragic element of the story so far? Petunia likes Vernon but he likes nobody. However, as the famous German author “Janosh” said, “if you are loved, you cannot help but giving a little bit of love back”. Let’s make it a happy end, shall we?

Vernon.likes = "Petunia"
print(Vernon.likes)

Puzzle 1: What is the output of this code snippet?

Let’s move on. Harry Potter would be boring without wizards. So let’s define the Wizard class so that we can create some wizards in our small world.

class Wizard:
    def __init__(self, age, name):
        self.age = age
        self.name = name
        self.mana = 100

    def like_me(self, victim):
        if self.mana >= 100:
            victim.likes = self.name
            self.mana = self.mana - 100


Wiz = Wizard(42, "Tom")

Every Wizard object has three variables: age, name, and mana level (how much magic power the wizard has left). On top of that, we add a method called like_me(...) that is a magic formula the wizard can apply to any victim. If the wizard has enough mana left, he can force the victim to like them.

Tom (aka. Lord Voldemort) is lonely and wants to be liked, so he tries to get Petunia and Vernon to like him:

Wiz.like_me(Petunia)
Wiz.like_me(Vernon)

print(Petunia.likes=="Tom" and Vernon.likes=="Tom")

Puzzle: Is Tom successful in making both like him?

Make sure that you have completely internalized the syntax of how to create classes and objects in Python. The most common source of confusion is to forget the self argument when defining a method and that the constructor is defined and called differently: __init__(...) vs Wizzard(...).

Puzzle Solutions

Puzzle 1: "Petunia"

Puzzle 2: False

Cheat Sheet OOP

To help you dive deeper into the most important features of Python object orientation, feel free to download the following PDF:

Download All 8+ Python Cheat Sheets

Download only this cheat sheet as PDF

Instagram Python OOP Tutorial

For an ultra-short Python object orientation tutorial, check out the following Instagram post (swipe right):

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Ein Beitrag geteilt von The Python Blog (@finxter.com_) am Nov 3, 2019 um 10:16 PST