How to direct this to file

Question

This is not direting to file p

with open('/var/tmp/out3') as f:
       before = collections.deque(maxlen=1)
       for line in f:
          if 'disk@g5000cca025a1ee6c' in line:
                sys.stdout.writelines(before)
          p.write(before)

have you declared `'p'` somewhere in your code? because there's no `p` defined in this code. you may need to declare `'p'` file, something like `with open('/var/tmp/out3') as f: with open('p_file.txt', 'w') as p:`...etc — chickity china chinese chicken, Jul 11 '17 at 18:42
ok good. your code works for me. what part doesn't work for you? do you get any errors? — chickity china chinese chicken, Jul 11 '17 at 19:46
TypeError: argument 1 must be string or read-only character buffer, not collections.deque — Ahmed, Jul 11 '17 at 19:55
you haven't assigned any contents to `deque` so `deque` doesn't have an output, instead you assigned `deque` to the variable `before`, and are trying to write the `deque` function to the file, which gives the error. you need to pass an iterable (some kind of `list`-like object to `deque` in the parentheses in this line --> `collections.deque(maxlen=1)`; you've only passed the parameter `maxlen` to `deque`, but it needs a `list` object. What contents does your `deque` contain? so far, it is empty — chickity china chinese chicken, Jul 11 '17 at 20:08
with open('/var/tmp/out3') as f: ... before = collections.deque(maxlen=1) ... for line in f: ... if 'disk@g5000cca025a1ee6c' in line: ... sys.stdout.writelines(before) ... before.append(line) ... 0. c0t5000CCA025A1EE6Cd0 — Ahmed, Jul 12 '17 at 13:35
I am getting the output as line but i want to direct output to file.means i want to direct this to file. — Ahmed, Jul 12 '17 at 13:35
@Downshift, I will explain as per my requirement.i want to grep an expression from a file and want one line above that expression to be written to other file. — Ahmed, Jul 12 '17 at 14:53
Please don't put `code` in comments, they don't format very well. Instead, click [edit](https://stackoverflow.com/posts/45041974/edit) and write your code into the question. — chickity china chinese chicken, Jul 12 '17 at 16:39
So you're requirement is while reading `/var/tmp/out3`, find a line containing an expression like `'disk@g5000cca025a1ee6c'`, if that line is found, write the previous line to a file `'p'`? — chickity china chinese chicken, Jul 12 '17 at 16:42
I've added code in an answer, please try it and let me know if it does not meet your requirement. Thank you. — chickity china chinese chicken, Jul 12 '17 at 18:04

chickity china chinese chicken · Accepted Answer · 2017-07-12T21:20:49.540

0

Try this:

import sys

filename = '/var/tmp/out3'
expression = 'disk@g5000cca025a1ee6c'

with open(filename, 'r') as f:
with open('p', 'w') as p_file:
    previous = next(f)
    for line in f:
        if expression in line:
            p_file.write(previous)
        previous = line

If the expression is found, you should find a file 'p' in your current directory containing the expression.

It worked when I tried it on Python2.7.10. I took the code from this answer Refer to previous line when iterating through file with Python.

Hope this helps.

edited Jul 12 '17 at 21:20

answered Jul 12 '17 at 18:04

chickity china chinese chicken

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The code worked thanks.But i need output to direct to another file – Ahmed Jul 12 '17 at 20:16
my mistake, you are right, I forgot to change the output to direct to the file instead. I've updated the answer. – chickity china chinese chicken Jul 12 '17 at 21:21
Glad it worked for you, please check-mark the answer "Accepted" if it answered your question. Thank you @Ahmed – chickity china chinese chicken Jul 12 '17 at 21:22
i am new to the site where i should check-mark.Please inform. – Ahmed Jul 12 '17 at 21:28
That's okay, no worries :) There should be a 'check mark' button you can press on the left side of the answer, check it 'green', look at this: [How does accepting an answer work?](https://meta.stackexchange.com/a/5235) thanks – chickity china chinese chicken Jul 12 '17 at 21:31
Great, glad it helped you. And thank you for accepting my answer, Sir. Cheers. – chickity china chinese chicken Jul 12 '17 at 21:56

How to direct this to file

1 Answers1