Script not writing to file

Question

I would like to make it so that it opens up alan.txt, search the text for all instance of scholary_tehologian and if found, add the word "test" under it. when I tried doing it this way:

## Script
with open('alan.txt', 'r+') as f:
for line in f:
    if "scholarly_theologian" in line:
        f.write("test")

it wouldn't write anything. I'm in Windows 8.1

That will just overwrite the next four characters with "test". — cdarke, Apr 18 '15 at 16:56
the file does have a line with "scholarly_theologian", I tested it. — user1666375, Apr 18 '15 at 16:56
Ok, so what I put "\ntest"? Creates a new line with the word test? — user1666375, Apr 18 '15 at 16:57
possible duplicate of [How do I modify a text file in Python?](http://stackoverflow.com/questions/125703/how-do-i-modify-a-text-file-in-python) — whereswalden, Apr 18 '15 at 17:24
If you wrote "\ntest" you would overwrite the next *five* characters. You cannot "insert" into a text file, you can only append. — cdarke, Apr 18 '15 at 19:38

manicphase · Answer 1 · 2015-04-18T18:59:20.340

1

Rewritten answer because the last one was wrong.

If you want to read lines you have to put .readlines() after open(...) or f. Then there's a few ways you could insert "test".

 ## Script
with open('alan.txt', 'r') as f:
    lines = f.readlines()

for i in range(len(lines)):
    if "scholarly_theologian" in lines[i]:
         lines[i] = lines[i] + "\ntest"

with open('alan.txt', 'w') as f:
    f.write("\n".join(lines))

edited Apr 18 '15 at 18:59

answered Apr 18 '15 at 16:57

manicphase

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the phrase I'm looking for is scholarly_theologian", even when I do this, it still doesn't work but thank you for answering my question. – user1666375 Apr 18 '15 at 17:01
Completely re-written the answer now. – manicphase Apr 18 '15 at 17:24
1

Use `xrange(len(lines))` instead of `range(lines)` – Ella Sharakanski Apr 18 '15 at 17:42
I meant before the one-liner edit. Now it's wrong again, it should be `"\n".join(lines)` like it was before – Ella Sharakanski Apr 18 '15 at 18:05

score 1 · Answer 2 · edited May 23 '17 at 11:51

You can't modify a file like this. You can only append to it, write characters instead of others, or rewrite it entirely. See How do I modify a text file in Python?.

What you should do is create another file with the content you want.

EDIT:

Claudio's answer has the code for what I offered. It has the benefit (over manicphase's code) of not keeping the whole file in memory. This is important if the file is long. manicphase's answer, on the other hand, has the benefit of not creating a second file. It rewrites the original one. Choose the one that fits your needs.

score 0 · Answer 3 · edited May 23 '17 at 11:51

This should do the trick:

with open('output.txt', 'w') as o:
    with open('alan.txt', 'r') as f:
        for line in f:
            o.write(line)
            if line.find('scholarly_theoligian'):
                o.write('test')

Like Ella Shar mentioned, you need to create a new file and add the new content into it.

If working with two files is not acceptable, the next step would be to delete the input file, and to rename the output file.

Script not writing to file

3 Answers3