Скачать или смотреть How to Reorder a List Composed of Lists in Python

Learn the efficient way to reorder a list of lists in Python. Get step-by-step guidance to troubleshoot your code effectively!
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This video is based on the question https://stackoverflow.com/q/71312781/ asked by the user 'Shawn Cheung' ( https://stackoverflow.com/u/17926932/ ) and on the answer https://stackoverflow.com/a/71312833/ provided by the user 'aminrd' ( https://stackoverflow.com/u/3279603/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Reorder a List Composed of Lists in Python

When working with lists in Python, you might encounter situations where you want to reorder sublists in a specific manner. This task can seem daunting, especially if the code isn't producing the desired output. In this guide, we’ll break down the solution to reorder a list comprised of lists, so you can effectively transform your data as needed.

The Problem

Consider the following situation: you have a list that contains other lists, and you'd like to reorder these sublists in a specific manner. For example, given the input [[1, 2, 3], [1, 2]], you want to generate an output like [[1, 2, 3], [3, 2, 1], [2, 3, 1], [1, 2], [2, 1]]. However, you find that your initial implementation is resulting in repeated entries like [[1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2], [1, 2]], which is not what you want.

The Solution

To achieve the desired output, you need to address a few key points in the code you use to reorder the list of lists. Here’s a simpler step-by-step approach to modifying your original idea.

Step 1: Understand the Code Issue

Firstly, in your initial code, you’re trying to append the same list reference (listTemp) multiple times. This leads to unintended repetition since every modification applies to the same object in memory. To fix this, you need to create a copy of the list each time before appending it to the result list.

Step 2: Update Your Function

Here’s the corrected function that reorders your lists correctly:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Understanding the Output

When you run the updated code above, you should now see the correct output:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code:

Creating a Copy: The line List2.append([x for x in listTemp]) ensures that each time you append to List2, you’re adding a new list created from listTemp rather than a reference to it.

Modification Logic: The operation t = listTemp.pop() removes the last element from listTemp and the next line inserts that element at the beginning of the list. This process continues during each iteration, gradually producing the new order of elements.

Conclusion

Reordering a list of lists in Python is a common task, and with the right adjustments, it can be performed smoothly. By ensuring you append a copy of the list rather than a reference, you can avoid repeated entries and achieve the desired list structure. Keep experimenting with lists, and don't hesitate to make minor adjustments in your process for maximum effectiveness. Happy coding!