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Discover how to create a custom deque class in Python by inheriting from collections.deque while excluding the appendleft method. Learn effective techniques to achieve this!
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This video is based on the question https://stackoverflow.com/q/68847661/ asked by the user 'Daniel Tomas' ( https://stackoverflow.com/u/16697530/ ) and on the answer https://stackoverflow.com/a/68847733/ provided by the user 'user2390182' ( https://stackoverflow.com/u/2390182/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Creating a Custom Deque Class in Python: Inheriting with No appendleft Method

In the world of Python programming, deque (double-ended queue) is an incredibly useful data structure that allows for fast appends and pops from both ends. However, there are instances where you might want to create a custom deque class that excludes certain methods. In particular, you may want to exclude the appendleft method but keep other functionalities intact. This blog will walk you through how to accomplish this while maintaining good coding practices.

The Problem Explained

You want to create a custom deque class that does not include the appendleft method. Your initial attempt at removing the method resulted in a TypeError, indicating that you cannot delete attributes from built-in types. This is a common roadblock that many developers face when trying to customize built-in classes in Python.

The Error You Encountered

When trying to delete the appendleft method directly, your code produced the following error:

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This error occurs because you cannot modify built-in types in Python directly, which leads us to explore alternative solutions.

Crafting the Solution

To tackle this problem effectively, we can take one of two approaches: raise an error for the appendleft method without modifying its attribute directly or utilize the _getattribute_ method to hide the attribute entirely. Let’s go through both methods step by step.

Method 1: Raising an Error on the appendleft Method

The first method is simple and straightforward; you can define the appendleft method in your custom class to always raise a NotImplementedError. This way, if anyone tries to use it, they'll quickly receive a clear error message.

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Example Usage

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Method 2: Hiding the appendleft Method Using _getattribute_

If you want to make it look like the appendleft method doesn't exist at all, you can override the _getattribute_ method. This will not only raise an error when trying to access the method directly but also when attempting to call it.

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Example Usage

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Additional Notes

It's worth noting that while the appendleft method won't be available in your custom class, you still have options for inserting elements at the beginning of the deque. You can use the insert method for this purpose, like so:

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Conclusion

Creating a custom deque class without certain methods is not only feasible but can be achieved through careful design choices. By understanding how to use Python's built-in capabilities effectively, you can customize classes to fit your specific needs. Whether you choose the NotImplementedError or override __getattribute__, both approaches have their merits.

If you have any questions or want to share your own experiences with customizing Python classes, feel free to leave a comment below!