Can I Modify File Lines In-Place While Iterating in Python?

Modifying Lines in a File In-Place

Is it possible to sequentially parse a file line by line and modify lines in-place while iterating through the file?

Answer:

Yes, this can be simulated through the use of a backup file, as implemented in the fileinput module within the Python standard library.

Example Code:

Consider the following script that removes lines that do not meet a specific condition specified by the some_condition function from provided files or standard input:

#!/usr/bin/env python
# grep_some_condition.py
import fileinput

for line in fileinput.input(inplace=True, backup='.bak'):
    if some_condition(line):
        print(line, end="")  # This outputs modified lines to the current file

Usage Example:

To utilize this script, execute the following command:

$ python grep_some_condition.py first_file.txt second_file.txt

Upon execution, both first_file.txt and second_file.txt will be modified to contain only lines that satisfy the some_condition predicate.

The above is the detailed content of Can I Modify File Lines In-Place While Iterating in Python?. For more information, please follow other related articles on the PHP Chinese website!