9221 of 11673 Respondents Answered This Poll Incorrectly

What happens when you instantiate a new object?

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This is a poll I asked on LinkedIn 6 months back:

What really surprised me here was that most Python programmers hugely misinterpret the __init__() in Python OOP.

They think that it is the first method that is executed when we create a new object, i.e., one that allocates memory to it.

But this is completely wrong.

To understand this, 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 is NEVER called first, and it 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:

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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:

The above explanation shows that __init__() is not the first method that is invoked when we create a new object.

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The internet is full of shallow resources that leave several knowledge gaps in the learner’s mind (which also explains the poll results above).

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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.

Also, lately, I have been finding Python Descriptors to be massively helpful in reducing work and code redundancy while also making the entire implementation much more elegant.

We covered it in this newsletter issue: Define Elegant and Concise Python Classes with Descriptors.

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

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For those who want to build a career in DS/ML on core expertise, not fleeting trends:

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• A Mathematical Deep Dive Into the Curse of Dimensionality

• A Crash Course on Graph Neural Networks – Part 1

• A Crash Course on Graph Neural Networks – Part 2

• A Crash Course on Graph Neural Networks – Part 3

• Formulating and Implementing XGBoost From Scratch

• A Crash Course of Model Calibration – Part 1

• A Crash Course of Model Calibration – Part 2

• Conformal Predictions: Build Confidence in Your ML Model’s Predictions

• Quantization: Optimize ML Models to Run Them on Tiny Hardware

• A Crash Course on Causality – Part 1

• A Crash Course on Causality – Part 2

• 5 Must-Know Ways to Test ML Models in Production (Implementation Included)

• A Beginner-Friendly Guide to Multi-GPU Model Training

• Implementing Parallelized CUDA Programs From Scratch Using CUDA Programming

• And many many more.

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