Python Class Methods: Class Vs. Instance Vs. Static Methods
In this article we are going to look at methods that we can use in Python classes. Methods are essentially functions within a class. In Python, we can use three (3) different methods in our classes: class methods, instance methods, and static methods. We are going to look at how each method differs from the other. Before we dive into the methods, let’s look at two types of attributes that we find in classes. Understanding class attributes is crucial to understanding methods.
Class Attributes
What is a class attribute? A class attribute is a variable that belongs to a class. It is a property of the class. It belongs to the class rather than any specific object. This attribute is created outside of the constructor method (__init__). Below, we have a code that demonstrates how we create class attributes in a class.
Instance Attributes
Class attributes (variables) belong to a class and not to a specific object. However, we can also create instances that belong to an object or instance. These attributes are called “instance attributes.” Instance attributes are created inside a constructor. The constructor for instance attributes is the __init__() method. The constructor initializes the instance attributes. The first parameter of the constructor is self. The attributes of the instance come after the “self” parameter. See the code below.
Class Methods
Class methods are methods that are not bound to an instance of a class (object) but to the class itself. Remember, there are two types of attributes in a class; class attributes and instance attributes. Class attributes are bound to the class, while instance attributes are bound to an object. Class methods can only access and modify class attributes and not instance attributes. There are two ways to create a class method. The first method is to use the classmethod() function. The second method is to use the @classmethod decorator. In this article, we are going to use the decorator to create a class method. The first parameter of this class method is “cls”. The “cls” keyword simply means “referring to the class.”
In our class below, there is a class attribute called “home.” We create a class method that can access and modify this class attribute. We create a function called “animals_home.” Right at the top of the function, we add the decorator @classmethod. This decorator converts the function into a class method. We use this method to change the class attribute. We change the home variable, from “Zoo” to “Jungle”. This proves that class methods can access and change class attributes.
Instance Methods
Now let’s look at instance methods. Instance methods can access and modify both class attributes and instance attributes. Similar to a class method, an instance method is just a function in a class. It also starts with the keyword “def”. Its first parameter is the keyword “self”. The self parameter binds the method to the instance object. In the code below, we have added an instance method called insta_method. Notice that this insta_method has access to the attributes of the object (name and age) and the class attributes (home). Notice that we have changed the class attribute (home) value from “zoo” to “jungle”. When we call the instance method using the animal1 (animal1.insta_method) object, you can see that the output for location says “jungle” instead of “zoo”. Instance methods are used more often than class methods because they can access both class and instance attributes.
Static Methods
Unlike instance and class methods, static methods cannot access class attributes or instance attributes. In Python, we create a static method using a decorator. We write @staticmethod right above the method we want to decorate. Static methods have no implicit first argument. Neither cls nor self is passed as the first argument. Static methods are just functions that you can call from the class or instance of the class. Below, we have added a static method to our code. This method takes one argument, which is the age of the animal, and checks if the animal is an adult or not. Notice that we are using the animal instance (animal1) to call the static method. Static methods are simply utility or helper functions. They add extra functionality to a class without accessing or modifying the class state.
Summary
Class methods can access class attributes, but they cannot access instance attributes. Instance methods can access both class and instance attributes. Static methods are just utility functions. They do not have access to class attributes or instance attributes.
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