如何仅替换文件中的一个指定行（在python中）

Question

I have a file and wanna replace a specific line that I can find it with search in file. I do that likes the following from this post :

import fileinput
new_line = 'some text'
with fileinput.FileInput(file_addr, inplace=True) as file:
    for line in file:
        if 'keyword' in line:
             line = new_line
             # Here #
        print(line)

Now I want to terminate the loop in # Here # . In this point, I found the line and replace it. But if I break the loop, the rest of the file will not be written into the file and will be removed. I am looking for a method just replace line when finding it and then terminate the loop. The reason is the length of the file could be high and I don't wanna loop over the rest of the file.

Also, if there is a solution for the both case that the length of new_line is the same as the length of the line or not (if it is matter).

Answer 1

You can only do this if the replacement line is the same length as the original line. Then you can do it by opening the file in read-write mode and overwriting the line in the file.

new_line = 'some text'
with open(file_addr, 'r+') as f:
    while True:
        line = f.readline()
        if 'keyword' in line:
            f.seek(-len(line), 1)
            f.write(new_line)
            break

Answer 2

You can turn the part of your code to generator:

lines = (line if 'keyword' not in line else new_line for line in file)

then you just write it to a file

with file(new_file, 'r') as new_file:
    new_file.writelines(lines)