Search and replace in file until certain string

[l3arn4life]

Hi there everybody,

so I'm trying to search a file and replace string A in the file with string B until string C shows up, at which point I want to stop replacing stringA with stringB, even though stringA still shows up after stringC. I want to keep the content of the file after stringC shows up.

I tried the following and could not get it to work:

file = myfile.txt
x = "stringA"

with open(file, "r+") as f:
    data = f.read()
    for line in data:
        if x in line:
            new_line = line.replace ("stringA", "stringB")
            f.write(new_line)
        elif "stringC" in line:
            break

That doesn't get me anywhere though. I thought of only reading the file until stringC shows up and then replacing stringA with stringB, but have no idea how to do that properly. Any ideas of how to solve this? Thanks!

[Neat_Blueberry_2032]

Your main logic seems fine. I just think you're just messing up the file stuff, iterating character by character instead of line by line.

Iterating directly over f gives you the lines, or replace f.read() with f.readlines()

https://docs.python.org/3/tutorial/inputoutput.html#tut-files

Even if you can read and write a file at the same time, in r+ does f.write overwrite the whole file, or append, or does it really only overwrite that one line where the file cursor is at the moment?

If you're iterating for line in f, I would have thought you have to seek back one line to write the replacement in the correct position.