Python Class: The Anatomy of a Python Class

Introduction

Python is an object-oriented programming language. This means that everything in Python is some kind of object that belongs to a class. In Python, we can create our own classes. A class is a template for creating objects, which are instances of the class. These objects have their own attributes (variables) and methods (functions), which are defined in the class. In this article, we will take a look at the anatomy of a Python class, including its components and how they work together.

The Basic Class Structure

The class is defined using the "class" keyword. After class comes the name of the class. The class name should be in PascalCase (i.e., the first letter of each word is capitalized), and it should be descriptive of the class's purpose.

The first method defined in a class is usually the __init__ method. This method is a special method that is called when an object of the class is created. The __init__ method is used to initialize the attributes of the object. The first parameter of the __init__ method is always "self," which refers to the object being created. The attributes defined inside this method are known as instance attributes.

Here's an example of a class called "Person" with an instance attribute (name) and a "greet" method.

In this example, the __init__ method initializes the name attribute (instance attribute) of the object when it is created. The "greet" method is an instance method. We are going to look at instance methods later.

To create an object of this class and call its methods, we would do the following:

In this example, p1 is an instance or object of the "Person" class. We use the object p1 to call the "greet" method.

Instance Methods

Apart from the __init__ method, a class can have other instance methods. An instance method is a method that is bound to an instance of a class and not the class itself. The first parameter is always "self," which refers to the object the method is being called on. It can access and modify the instance variables, and it can also access class variables (we will look at class variables next). Here's an example of an instance method being used in a class:

In this example, we are using the instance of the class (obj1) to call the instance method.

Class Methods and Class Variables

Class methods are defined using the @classmethod decorator, which takes "cls" (the class name) as its first parameter. These methods are bound to the class and not the object. In addition to the methods, a class can also have class variables. Class variables are variables that are shared by all objects (instances) of the class. Class variables are defined outside of any method, usually at the top of the class definition. Class methods can access and modify class variables. Here is an example:

In this example, the class method is accessing the class variable. The class method is also accessed through the class itself (MyClass.class_method()) and through the object of the class (obj1.class_method()).

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Magic Methods

In addition to the class and instance variables and methods, Python classes also have special methods, also known as magic methods. These methods have double underscores at the beginning and end of their names (e.g., __str__, __add__). These special methods allow us to customize the behavior of the class when certain operations are performed on it. This is known as operator overloading. For example, the __str__ method is called when we use the built-in print() function on an object of the class and allows us to define what should be printed. See the example below:

In this example, when we use the print() function on the p1 object, it calls the __str__ method defined in the class. This method returns the string "Person: Mike."

Another example of a special method is the __add__ method, which allows us to customize the behavior of the addition + operator when used on objects of the class. Here's an example:

In this example, when the + operator is used on the v1 and v2 objects, the class-specified __add__ method is invoked. The return value of this method is a new Vector object that has x and y values equal to the sum of the x and y values of the two original Vector objects.

These are just a few of the numerous special methods that Python offers. These unique methods allow us to modify a class's behavior, enhancing its adaptability.

Conclusion

In conclusion, a Python class is a template for creating objects, which are instances of the class. Classes can have methods and variables. The class defines these methods and variables, which can be used to alter how the class and its objects behave. To write Python code that is effective and flexible, it is crucial to comprehend the anatomy of a Python class. Thank you for reading. Please share this story and subscribe to this newsletter if you are not yet a subscriber. You can also follow me on LinkedIn.

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