Скачать или смотреть How to Replace Lines in a File using Python with Custom Replacements

Discover a straightforward method to replace specific lines in a Python file based on matching characters using a list of replacements. Learn step-by-step how to implement this.
---
This video is based on the question https://stackoverflow.com/q/73359587/ asked by the user 'Ash141' ( https://stackoverflow.com/u/19767146/ ) and on the answer https://stackoverflow.com/a/73359924/ provided by the user 'D.L' ( https://stackoverflow.com/u/7318120/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Replace all lines containing a certain character with elements from a list, iterating through each element for each line in input

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Introduction

Are you facing a challenge with replacing specific lines in a text file with elements from another list in Python? If you've got an input file containing various lines and you want to substitute occurrences of lines containing a specific character with different entries from another file, you've come to the right place! This post will guide you through an effective solution to this problem using Python.

The Problem Statement

Imagine you have an input file, let’s call it original.txt, which has several lines. You also have a second file, H.txt, that contains a list of replacement lines. The task is to replace the first line in original.txt that contains the character "H" with the first line from H.txt, the second occurrence of "H" with the second line from H.txt, and so forth. This needs to be done within Python, iterating through each occurrence correctly while handling the replacements gracefully.

The Solution

We have two main methods to approach this problem, both of which involve reading the contents of your replacement file into a list and replacing occurrences accordingly. Let’s break down each method for clarity.

Method 1: Using List and Pop

This method involves reading the content of H.txt as a list and using the pop() function to remove the first element when it’s used. However, this can be less straightforward as it modifies the original list.

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

While effective, modifying the list in-place can lead to issues if the number of replacements exceeds the size of the list.

Method 2: Using a Counter

A more intuitive way to handle the replacements involves keeping a counter that tracks your current position in the replacement list. This helps ensure you always replace lines in a manageable manner without modifying the original list directly.

Implementation Example

Here’s how you can implement this method within your code:

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

How Does It Work?

Read Files: The code begins by opening and reading the original and replacements files into lists.

Initialize: It sets up an empty list output_lines to store the modified lines and an index i to track your current replacement position.

Iterate and Replace: The code loops through each line in the original file. If it detects a line containing "H," it replaces it with the corresponding term from terms. If i exceeds the length of terms, it resets so that you can reuse replacements if needed.

Output: Finally, it writes the new content to the output file.

Conclusion

With the methods laid out in this post, you can easily customize how you replace content within a file based on specific conditions. Whether you choose to use pop() to modify the list directly or to maintain an index counter to manage replacements, Python offers you the tools to achieve your goals effectively. Armed with this knowledge, you can tackle line replacements in text files with confidence. Happy coding!