Altcademy - a Forbes magazine logo Best Coding Bootcamp 2023

What is a constructor in Python

Understanding Constructors in Python

When you're starting your journey in programming, you might come across the term "constructor." It's a concept that exists in many programming languages, including Python. But what exactly is it? Let's break it down into simple terms.

Imagine you're a chef. Each time you prepare a dish, you start with a recipe that outlines the specific ingredients and steps needed to create that dish. In programming, a constructor can be thought of as a recipe for creating an object. An object is a collection of data (ingredients) and methods (instructions) that together represent a concept or thing in your code.

In Python, a constructor is a special method of a class. A class is like a blueprint for objects; it defines the shape and nature of what an object will be. The constructor's job is to initialize (set up) the object's state by assigning values to its properties when the object is created.

The __init__ Method: Python's Constructor

The most common type of constructor in Python is the __init__ method. This method is called automatically when you create a new instance of a class. "Instance" here simply means a specific example of the class, much like a single dish made from a recipe.

Here's a simple example:

class Dog:
    def __init__(self, name, breed): = name
        self.breed = breed

    def bark(self):
        print(f"{} says woof!")

# Creating an instance of Dog
my_dog = Dog("Rex", "German Shepherd")

# Using the bark method

In this example, Dog is a class with an __init__ method. The __init__ method takes three parameters: self, name, and breed. The self parameter is a reference to the current instance of the class, and it's how you access properties and methods from within the class code.

When we create my_dog, we pass "Rex" and "German Shepherd" to the __init__ method, which sets the name and breed properties of the object. Then, when we call my_dog.bark(), it prints out "Rex says woof!"

Why Use Constructors?

Constructors serve several important purposes in object-oriented programming:

  1. Initialization: They allow you to set the initial state of a new object. Without a constructor, you'd have to set each property manually after creating the object.
  2. Consistency: They help ensure that objects are created with a valid state, reducing the chance of errors.
  3. Convenience: They can make it easier and cleaner to create objects, especially when the object requires a lot of setup.

Default Constructors

If you don't explicitly define an __init__ method in your class, Python will provide a default constructor that doesn't do anything. This is like having a basic recipe that just tells you to "combine ingredients" without specifying what those ingredients are.

Here's an example:

class Cat:
    def purr(self):

# Creating an instance of Cat
my_cat = Cat()

# Using the purr method

In this Cat class, we didn't define an __init__ method, so Python uses a default one. You can still create instances of Cat and call its methods.

Advanced Constructor Features

The self Parameter

The self parameter is a bit like the word "my" in English. When you say "my shirt," you're referring to the shirt that belongs to you. Similarly, self refers to the specific object that belongs to the class.

Additional Parameters

You can pass as many parameters as you need to an __init__ method, just like you can add as many ingredients as you want to a recipe.

Default Parameter Values

You can give parameters default values, which is like saying "if you don't have this ingredient, use this other one."

class Bird:
    def __init__(self, color="yellow"):
        self.color = color

    def sing(self):
        print(f"The {self.color} bird is singing.")

# Creating instances of Bird with and without specifying the color
yellow_bird = Bird()
blue_bird = Bird("blue")

yellow_bird.sing()  # Outputs: The yellow bird is singing.
blue_bird.sing()  # Outputs: The blue bird is singing.

When Things Go Wrong

If you've ever followed a recipe and forgotten an ingredient, you know it can lead to unexpected results. The same goes for constructors. If you forget to pass a required parameter, Python will raise a TypeError.

Intuition and Analogies

To understand constructors intuitively, think of them as the starting point of a story. Just like a story sets the scene and introduces the characters, a constructor sets up the object and gives it its initial characteristics.

Another analogy is building a house. The constructor is like laying the foundation and setting up the basic structure. Without a solid foundation, your house (or object) won't be stable.


Constructors in Python are the secret ingredients that get your objects ready for action. They're the behind-the-scenes magic that, while not always visible in the final product, are crucial to its creation and stability. As you continue to learn and experiment with Python, you'll find that understanding and using constructors effectively will help you write cleaner, more efficient code. So next time you're coding, think of yourself as a chef or a storyteller, and make sure your objects have the strong, well-defined beginnings they deserve. Happy coding!