Classes and Objects

Learn how to create classes and objects in MicroPython

Introduction

In this lesson, we will explore the concepts of classes and objects in MicroPython. Understanding these concepts is fundamental to mastering object-oriented programming (OOP) and will help you build more organized and reusable code.

What is a Class?

A class is a blueprint for creating objects. It defines the properties and methods that an object will have. In MicroPython, you can define a class using the class keyword.

An instance of a class is also known as an object. By instance, we mean a single occurrence of an object:

a = 1         # a is an instance of an integer object
b = "hello"   # b is an instance of a string object
c = [1, 2, 3] # c is an instance of a list object

Properties and Methods

A class property is the name we give to variables within a class. A class method is the name we give to functions within a class.

class Robot:
    robot_name = "" # this is a class property
    color = ""      # this is another class property

    def say_hello(self):
        # This is a class method
        print(f"Hello, I am {self.robot_name}")

    def change_color(self, new_color):
        # This is another class method
        self.color = new_color

Classes Model the Real World

We use classes to model real-world things, such as a Robot or a Car. For example, we can create a class called Robot with properties like robot_name and color, and methods like say_hello and change_color—similar to a real-world robot.

class Robot:
    robot_name = ""

    def __init__(self, name, color):
        self.robot_name = name
        self.color = color

    def say_hello(self):
        print(f"Hello, I am {self.robot_name}")

    def change_color(self, new_color):
        self.color = new_color

You can create multiple objects from the same class, each with its own set of properties and methods. Note that property values can differ for each object, but the methods remain the same.

r2d2 = Robot("R2D2", "Blue")
c3po = Robot("C3PO", "Gold")

Constructors

Notice the __init__(self, name, color) method in the Robot example above. This is called the constructor of the class. It is called when a new object is created from the class.

We use the constructor to set the initial values of the object’s properties.

Naming Conventions & Indentation

The convention is to name classes with an uppercase letter at the start of each word. In the example above, we have a class called Robot.

Notice how the methods within the class are indented. This means these methods are only accessible within the class or via the dot “.” operator.

Also, notice that there is a variable called robot_name within the class. This is a class variable shared by all instances of the class.

What is an Object?

In Python and MicroPython, an object is an instance of a class. It is created using the class as a blueprint.

An object is like a variable that also has functions attached to it. These functions are the class methods.

You can call the methods of an object using the dot “.” operator.

# Create an object of the Robot class
r1 = Robot("R2D2", "Blue")

# Call the say_hello method
r1.say_hello()

# Change the color of the robot
r1.change_color("Red")

# Access the color of the robot
print(r1.color)

Everything in Python is an Object

Almost everything in Python is an object, including int, float, list, dict, and str. This means they have properties and methods that you can access.

You may have already used objects and their methods without realizing it. For example, the str object has a method called upper() that converts the string to uppercase.

message = "hello" # create a string called message and store the value "hello"
print(message.upper()) # prints out the message string in uppercase, this uses the str object's upper() method

What is Self?

In the __init__ method and other class methods, you will see a parameter called self. This is a reference to the current instance of the class. It is used to access the variables and methods of the class.

self is always the first parameter in a class method; it cannot be omitted.

class Robot:
    # Class Properties
    robot_name = "" # this is a class property
    color = ""      # this is another class property

    def __init__(self, name, color):
        self.robot_name = name # changes this object's robot_name to the name provided
        self.color = color     # changes this object's color to the color provided

    def change_color(self, new_color):
        # This is a class method
        self.color = new_color

Did You Know?

“self” can actually have any name, but it is a convention to use “self” in Python.

You could use “this” or “me” or any other name, but it is best to stick with “self” to avoid confusion. As long as the first parameter of a class method is the reference to the current instance of the class, it will work.

Summary

In this lesson, we’ve learned about classes and objects in MicroPython. We explored how classes act as blueprints for creating objects, how to define properties and methods, and the importance of the self parameter. We also covered naming conventions and the concept that everything in Python is an object.

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