Python search string and replace character in next line

Question

in a text file I want to search for a line containing specific text and at the next line I want to substitute beginning of a line with #(comment it out) inplace:

Example - before:

#test search 123
text to be commented out
#test 123

Example - wanted:

#test search 123
#text to be commented out
#test 123

I can do it via sed:

sed -i '/^#test search 123/!b; n; s/^/#/' test_file

but i was wondering if I'm able to do it natively in python.

possible duplicate of 'in-place' string modifications in Python — fedorqui
– fedorqui, Commented Jun 19, 2015 at 10:37
your sed is at least suspicious. correct will be sed -i '/pattern/ {N; s/\n/\n#/}' file. Any python solution will be longer. — josifoski
– josifoski, Commented Jun 19, 2015 at 11:21

Lazik · Accepted Answer · 2015-06-19 11:02:24Z

1

import os

outfile = open('bla.txt.2', 'w')

search = "#test search 123"
flag = 0

with open('bla.txt', 'r') as f:

    for line in f:
        if flag == 1:
            mod_line = "#" + line
            outfile.write(mod_line)
            flag = 0
            continue

        outfile.write(line)
        if (search in line):
            flag = 1

outfile.close()

os.remove('bla.txt')
os.rename('bla.txt.2', 'bla.txt')

answered Jun 19, 2015 at 11:02

Lazik

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2 Comments

radoslav Over a year ago

Thanks for answering. Works!!! So there is no chance to do the editing in-place without the second temp. file?

Lazik Over a year ago

Not really, you could look into fileinput inplace but it still creates a temp backup file, so no dice.

josifoski · Accepted Answer · 2015-06-19 11:39:29Z

0

Correct sed will be

sed -i '/pattern/ {N; s/\n/\n#/}' file

This which follows maybe is not most pythonic way of same, specially if import re is needed for more complicated pattern then simple string

#! /usr/bin/env python3

pattern='some text'
f = open('input.txt', 'r')
g = open('output.txt', 'w')
l=f.readlines()
f.close()
for ind in range(len(l)):
    if pattern in l[ind]:
        l[ind+1]='#' + l[ind+1]
for field in l:
    g.write(field)
g.close()
print('Done')

answered Jun 19, 2015 at 11:39

josifoski

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