Python replace line by index number

Question

Is it possible in Python to replace the content of a line in a file by its index number?

Would something like a line.replace to do this procedure?

possible duplicate of [Search and replace a line in a file in Python](http://stackoverflow.com/questions/39086/search-and-replace-a-line-in-a-file-in-python) — dting, May 11 '15 at 06:30
@m170897017 Yes of a specific file, the file is dynamic and i have a function which gets me the line number i want to replace, but how can i replace the found line now ^^ ? — HightronicDesign, May 11 '15 at 06:33

score 4 · Accepted Answer · answered May 11 '15 at 06:59

4

If you wish to count iterations, you should use enumerate()

with open('fin.txt') as fin, open('fout.txt', 'w') as fout:
    for i, item in enumerate(fin, 1):
        if i == 7: 
            item = "string\n" 
        fout.write(item)

answered May 11 '15 at 06:59

John La Rooy

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1

this solution works party for me, i am able to replace the line, but its going to copy me the complete file and paste it under the original ... – HightronicDesign May 11 '15 at 08:57
solved: i've written an a+ as argument for fout instead of an w. THX – HightronicDesign May 11 '15 at 09:00

hungnv · Answer 2 · 2015-05-11T07:33:48.000

0

something likes:

count = 0
with open('input') as f:
    with open('output', 'a+') as f1:
        for line in f:
            count += 1
            if count == 7: 
                line = "string\n" 
            f1.write(line)

edited May 11 '15 at 07:33

answered May 11 '15 at 06:33

hungnv

152
8

`++count` doesn't do what you think, in fact it effectively does nothing. I think you meant `count += 1` – mhawke May 11 '15 at 06:38
change ++count to count+=1 – Stephen Lin May 11 '15 at 06:39
Ok, i tried this way, but nothing happens, line remains the same. – HightronicDesign May 11 '15 at 08:48

score 0 · Answer 3 · answered May 11 '15 at 09:17

from tempfile import mkstemp
from shutil import move
from os import remove, close

def replace(file_path, pattern, subst):
    # Create temp file
    fh, abs_path = mkstemp()
    with open(abs_path, 'w') as new_file:
        with open(file_path) as old_file:
            for line in old_file:
                new_file.write(line.replace(pattern, subst))
    close(fh)
    #Remove original file
    remove(file_path)
    #Move new file
    move(abs_path, file_path)

You can use the above function to replace a particular line from a file, and you can call this function when needed as:

replace("path_of_File\\test.txt", "lien that needs to be changed", "changed to ")

hope this is the one you might be looking for....

score 0 · Answer 4 · answered Jan 18 '16 at 18:23

Well I used some of the answers above and allowed for user input to be put in the file. This also prints out the line that the user input will replace.

Note that filename is a placeholder the true filename.

import os, sys
editNum=int(editLine)
filename2="2_"+filename
with open(filename, "a+") as uf, open(filename2, "w+") as outf:
    for i, item in enumerate(uf, 1):
    #Starts for loop with the "normal" counting numbers at 1 instead of 0
        if i != editNum:
            #If the index number of the line is not the one wanted, print it to the other file
            outf.write(item)
        elif i == editNum:
            #If the index number of the line is the one wanted, ask user what to replace line with
            print(item)
            filereplace=raw_input("What do you want to replace this line with? ")
            outf.write(filereplace)
    #Removes old file and renames filename2 as the original file
    os.remove(filename)
    os.rename(filename2, filename)

Python replace line by index number

4 Answers4

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