{"id":17672,"date":"2020-11-15T04:05:08","date_gmt":"2020-11-15T12:05:08","guid":{"rendered":"https:\/\/careerkarma.com\/blog\/?p=17672"},"modified":"2023-12-01T04:04:02","modified_gmt":"2023-12-01T12:04:02","slug":"python-class-variables","status":"publish","type":"post","link":"https:\/\/careerkarma.com\/blog\/python-class-variables\/","title":{"rendered":"Python Class Variables vs. Instance Variables"},"content":{"rendered":"\n

Python is an object-oriented programming language that allows programmers to define objects which can contain data. Python variables<\/a> let you store particular values in a program.<\/p>\n\n\n\n

When you\u2019re working with objects in Python, there are two types of variables you may encounter\u2014instance variables and class variables. But what do these types of variables mean, and how do they work?\n\n<\/p>\n\n\n\n

That\u2019s the question we\u2019re going to answer in this guide. This tutorial will explore, with examples, the basics of class and instance variables, and how they are used within Python objects.\n\n<\/p>\n\n\n\n

Python Class Variables<\/h2>\n\n\n\n

A Python class variable is shared by all object instances of a class. Class variables are declared when a class is being constructed. They are not defined inside any methods of a class.<\/p>\n\n\n\n

Because a class variable is shared by instances of a class, the Python class<\/a> owns the variable. As a result, all instances of the class will be able to access that variable. Class variables are shared by all instances that access the class.<\/p>\n\n\n\n

Here is an example of a class variable in Python:<\/p>\n\n\n\n

class Espresso:\n\tmenu_type = "Drink"\n<\/pre><\/div>\n\n\n\n
In this example, we declare a class variable called menu_type<\/em>. This class variable is assigned to the class Espresso.<\/p>\n\n\n\n
Class variables are useful because they allow you to declare a variable when a class has been built, which can then be used later in your class. <\/p>\n\n\n\n
Like regular variables, class variables can store data of any type. So, we could store a Python dictionary<\/a>, a Python t<\/a>uple<\/a>, or a Python list<\/a> in a class variable.<\/p>\n\n\n\n
Accessing a Class Variable in Python<\/h3>\n\n\n\n
Now that we\u2019ve declared a class variable, we can access it when we create an object of our class. So, if we want to create a new class instance and see the value of the menu_type<\/em> variable, we could use this code:<\/p>\n\n\n\n
class Espresso:\n\tmenu_type = "Drink"\n\nespresso_order = Espresso()\nprint(espresso_order.menu_type)\n<\/pre><\/div>\n\n\n\n
Our code returns: Drink<\/em>.\n\n<\/p>\n\n\n\n
In our code, we first define a class that has one class variable: menu_type<\/em>. Then, we create an instance of our class. This instance is called espresso_order<\/em>.\n\n<\/p>\n\n\n\n
In order to see the value of the menu_type<\/em> variable in our class, we use the dot notation. This is the name of the class followed by a period. Then, we specify the name of the class variable you want to read. This causes our program to return Drink<\/em>.\n\n<\/p>\n\n\n\n
Because our class variable is associated with a class, we don\u2019t even need to declare an instance of our class to see its value. The following code allows us to see the value of our menu_type<\/em> class variable:<\/p>\n\n\n\n
class Espresso:\n\tmenu_type = "Drink"\n\nprint(Espresso.menu_type)\n<\/pre><\/div>\n\n\n\n
Our code returns: Drink<\/em>. In this example, we use the dot notation to access the value of the menu_type<\/em> variable in our Espresso class. Unlike our previous example, we do not declare an instance of our class.<\/p>\n\n\n\n
Changing a Class Variable<\/h3>\n\n\n\n
Class variables can also be changed, just like any other type of variable. To do so, you can use this code:<\/p>\n\n\n\n
class Espresso:\n\tmenu_type = "Drink"\n\nespresso_order = Espresso()\nespresso_order.menu_type = "Coffee"\nprint(espresso_order.menu_type)\n<\/pre><\/div>\n\n\n\n
Our code returns: Coffee<\/em>. In this example, we have declared an instance of our class called espresso_order<\/em>. Then, we assign the value of the espresso_order.menu_type<\/em> class variable to be equal to Coffee<\/em>. This changes the value of the variable.\n\n<\/p>\n\n\n\n
We print out the new value of the menu_type<\/em> variable to the console using a Python print statement<\/a>.<\/p>\n\n\n\n
Python Instance Variables<\/h2>\n\n\n\n
Python instance variables are owned by an instance of a class. The value of an instance variable can be different depending on the instance with which the variable is associated.\n\n<\/p>\n\n\n\n
This means that the value of each instance variable can be. This is unlike a class variable where the variable can only have one value that you assign. Instance variables are declared inside a class method.\n\n<\/p>\n\n\n\n
Here is an example of two instance variables in Python:<\/p>\n\n\n\n
class CoffeeOrder:\n\tdef __init__(self, coffee_name, price):\n\t\tself.coffee_name = coffee_name\n\t\tself.price = price\n<\/pre><\/div>\n\n\n\n
In this example, coffee_name<\/em> and price<\/em> are instance variables that exist within our class.<\/p>\n\n\n\n
Assinging Values to an Instance Variable in Python<\/h3>\n\n\n\n
We can assign values to an instance variable when we declare a class. We do this by specifying the values we want to assign as arguments when we declare the class. Suppose we want to create an instance of our class with the following values:\n\n<\/p>\n\n\n\n