How to keep lines which contains specific string and remove other lines from .txt file?

Question

Example: I want to keep the line which has word "hey" and remove others.

test.txt file:

first line

second one

heyy yo yo

fourth line

Code:

keeplist = ["hey"]
with open("test.txt") as f:
    for line in f:
        for word in keeplist:

`if word in line: print(line)` now you just need to write to a file instead of printing — Caridorc, Feb 12 '23 at 00:41
this should be the result? ```keeplist = ["hey"] with open("test.txt", "r+") as f: for line in f: for word in keeplist: if word in line: f.writelines(line)``` — Karim Mostafa, Feb 12 '23 at 00:48
like this you are writing to the old file `f` without deleting what comes before — Caridorc, Feb 12 '23 at 00:49
In your example, is "heyy yo yo" included because it contains the string "hey", or excluded because its not the _word_ "hey"? — tdelaney, Feb 12 '23 at 00:50
i think it should be this then ```with open("test.txt", "r+") as f: for line in f: if line.__contains__("hey"): f.truncate(0) f.writelines(line) f.close()``` — Karim Mostafa, Feb 12 '23 at 00:53

score 2 · Accepted Answer · answered Feb 12 '23 at 00:53

Its hard to remove lines from a file. Its usually better to write a temporary file with the desired content and then change that to the original file name.

import os

keeplist = ["hey"]
with open("test.txt") as f, open("test.txt.tmp", "w") as outf:
    for line in f:
        for word in keeplist:
            if word in line:
                outf.write(line)
                break
os.rename("test.txt.tmp", "test.txt")

How to keep lines which contains specific string and remove other lines from .txt file?

1 Answers1