Edit specific line in a big file

Question

I want to edit a a big file in specific lines. So it isnt a good Idea to read the whole file before editing, thats why I dont want to use:

myfile.readlines()

I have to read each line check if there a special content in it and then i have to edit this line.

So far Im reading every line:

file = open("file.txt","r+")
i = 0
for line in file:
    if line ......:
        //edit this line
        //this is where i need help


file.close()

So the Question is: How can I edit the current line in the If Statement for example: if the current line is "test" I want to replace it with "test2" and then write "test2" back into the file into the line where "test" was before

line is going to be a str object, so just treat is as you would treat any str object.. — EzzatA, Sep 20 '18 at 07:50
ok and how can i write the edited string back in to the file at the same line as the one before was ? — Loois95, Sep 20 '18 at 07:50
I'd suggest you read this, http://stupidpythonideas.blogspot.com/2013/06/readlines-considered-silly.html — EzzatA, Sep 20 '18 at 07:54
i think you didnt get my problem.... i know that i shouldnt use "readlines" thats why I'm not using it. My problem is to write the edited line back into the line where it was before i edited it. — Loois95, Sep 20 '18 at 08:02
Is the new line *exactly* the same length as the old line? if not then just overwriting it will either leave old data or will overwrite part of the next line. — cdarke, Sep 20 '18 at 08:06
Ahhhh ok, sorry, well, lines in File are not organized by lines, so its extremely hard, so, the most efficient way is to save a new file with the new data, https://stackoverflow.com/a/23598472/1400926 — EzzatA, Sep 20 '18 at 08:08
BASH to the rescue. Go here > https://stackoverflow.com/a/11145362/8726146 — MaJoR, Sep 20 '18 at 09:36

score 2 · Accepted Answer · answered Sep 20 '18 at 07:52

2

This will help

import fileinput

with fileinput.FileInput(filename, inplace=True, backup='.bak') as file:
    for line in file:
        print(line.replace(text_to_search, replacement_text), end='')

answered Sep 20 '18 at 07:52

Rahul Agarwal

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score 0 · Answer 2 · answered Sep 20 '18 at 08:24

ok so as @EzzatA mentioned in the comments below the question it seems to be the best way to read the original file and create a new one with the edited data. So something like this:

original_file = open("example.txt","r")
new_file = open("example_converted.xml","w")

string_tobe_replace = "test"
replacement_string = "test2"

for line in original_file:
    if string_tobe_replace in line:
        new_line = line.replace(string_tobe_replace,replacement_string)
        new_file.write(new_line)
    else:
        new_file.write(line)



original_file.close()
new_file.close()

Edit specific line in a big file

2 Answers2