Скачать или смотреть Comparing Two Lists in Python: Finding the Last Match Index and Value

Learn how to compare two lists in Python while stopping at the first mismatch and retrieve the index and value of the last matching item. Perfect for file path comparison and similar tasks!
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This video is based on the question https://stackoverflow.com/q/64504835/ asked by the user 'BenjaminK' ( https://stackoverflow.com/u/12211148/ ) and on the answer https://stackoverflow.com/a/64504904/ provided by the user 'Andrej Kesely' ( https://stackoverflow.com/u/10035985/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Comparing Two Lists in Python: Finding the Last Match Index and Value

When working with lists in Python, you may often find yourself needing to compare elements from two lists. In this guide, we will address a common problem where you want to compare two lists in their existing order and find the index and value of the last element that matches before the first mismatch occurs.

The Problem

Consider the case where we have two lists representing file paths or any hierarchical structure. Your task is to compare each corresponding element of the two lists. The comparison should stop as soon as a pair of elements is not equal, and you need to capture the index and value of the last matching item.

Here are our sample lists for reference:

List 1 (nk_script_file_path):

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

List 2 (node_filepath):

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

In this example, we want to determine up to which point the items in both lists are equal, and if they differ, we want to know the index of the last matching element.

The Solution

Using zip() and enumerate()

The most efficient way to solve this problem is by using a combination of Python's zip() and enumerate() functions. Here’s how it works:

zip(): This function allows you to iterate over two (or more) lists in parallel. It combines elements from both lists into pairs.

enumerate(): This function allows you to keep track of the index counter as you iterate over the elements.

Step-by-step Implementation

Here is the code that compares the two lists and finds the index of the last matching element:

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

What the Code Does:

The zip(lst1, lst2) pairs the elements of lst1 and lst2 together.

The enumerate() function provides an index i for each paired elements a and b.

If a is not equal to b, the loop breaks, and the last index i is determined.

If all elements are equal, i is set to -1.

Output Explanation

When the above code is run, it compares the two lists and returns:

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

This means that the last equal item was at index 3 with the value 1910_My_Project.

Conclusion

By using zip() and enumerate(), you can easily compare two lists in Python until a mismatch is found. This is a powerful technique that not only helps in comparing file paths but can also be applied in various scenarios where list comparison is needed.

Feel free to try this code with your own lists and customize it further as per your requirements. Happy coding!