How Can I Efficiently Search and Replace Text Within Files Using Python?

Search and Replace Lines in Files with Python

Suppose we have a text file and want to modify specific lines by replacing a certain word with another. We initially consider loading the entire file into memory for processing and writing it back. However, a more efficient approach exists.

Using the fileinput Module

The fileinput module offers a straightforward solution. By utilizing its input() function, we can iterate over the file line by line while modifying it in-place. Here's an example:

This code replaces occurrences of 'foo' with 'bar' in the file, line by line. As fileinput writes directly to the original file, no intermediate file is created.

Alternative Approaches

For small files, an alternative approach involves:

1. Reading the file into memory as a string.
2. Performing the search and replace operation.
3. Writing the modified string back to the file.

For larger files, consider:

1. Creating a temporary file.
2. Reading the original file line by line, performing the substitution, and writing to the temporary file.
3. Deleting the original file and renaming the temporary file to its place.

This approach requires additional temporary storage space but is efficient for large files.

Conclusion

Depending on the file size and specific requirements, these approaches provide efficient methods for searching and replacing lines in a file using Python.

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