The Most Common Misconception About init() Method in Python

Demystifying the init() method.

Jan 19, 2024

Most Python programmers misinterpret the __init__() magic method in Python OOP. They think that it creates a new object, i.e., allocates memory to it.

For instance, consider the Point2D class below:

Please assume that there is also a __repr__() method, as it is not shown here.

When we create an object (shown below), programmers believe that in the background, it is the __init__() method that is allocating memory to their object:

But that is not true.

When we create ANY object in Python, the __init__() method NEVER allocates memory to it.

As the name suggests, __init__() only assigns value to an object’s attributes, i.e., initialize the attributes.

Instead, it’s the __new__() magic method that creates a new object and allocates memory to it.

To understand better, consider the class implementation below.

Here, we have implemented the __new__() method, which checks if the passed arguments are of integer type.

Now, if we try to create an object of this class, Python would first validate the checks specified in the __new__ () method and create a new object only when the specified conditions are true.

This is evident from the image below:

Another popular use case of the __new__ method is to define singleton classes — classes that can only have one object.

For instance, consider the following class implementation:

In the above code, the __new__ method define a class variable _class_count.

When a new object is instantiated, if the value of _class_count=0, the value of _class_count is updated to 1 and the object is returned.

After creating the first object, a new object can never be created because the value of _class_count will never be 0.

This is evident from the image below:

Here’s a full deep dive into Python OOP if you want to learn more about advanced OOP in Python: Object-Oriented Programming with Python for Data Scientists.

👉 Over to you: What are some other use cases of __new__ magic method?

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