How to write to beginning and end of every line in a text file?

Question

I'm currently looking for a way to write to the beginning and end of every line of a text file in Python.

For example,

Current TXT document:

Jimmy
Was
Here

Write the 1st VALUE to the beginning of every line

111Jimmy
111Was
111Here

Write the 2nd VALUE to the end of every line

111Jimmy222
111Was222
111Here222

Can't seem to find anything on Google that describes how to properly have this done. I've found methods of writing to specific lines, but not all of them in this way.

http://stackoverflow.com/questions/125703/how-do-i-modify-a-text-file-in-python#125759 — Artium, Oct 28 '11 at 18:53

score 12 · Accepted Answer · answered Oct 28 '11 at 18:53

12

prefix = '111'
suffix = '222'

with open('source.txt', 'r') as src:
    with open('dest.txt', 'w') as dest:
       for line in src:
           dest.write('%s%s%s\n' % (prefix, line.rstrip('\n'), suffix))

answered Oct 28 '11 at 18:53

Steven Rumbalski

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what if `suffix` is not fixed length string ? – Bheid Feb 16 '16 at 09:18
@BehnamHeydari: That should make no difference. – Steven Rumbalski Feb 16 '16 at 17:37
so the number of `%s` is not related to length of `suffix`? – Bheid Feb 17 '16 at 04:11
1

@BehnamHeydari: Correct. Three `%s` means three items are being interpolated into the string. Here the three items are the prefix, the line itself, and the suffix. – Steven Rumbalski Feb 17 '16 at 16:37
For people using Python 3.6+, you can use f-strings (but note, [can't put `\n` inside the brackets](https://stackoverflow.com/a/44780467/2745495)): `ss = line.rstrip('\n'); dest.write(f"{prefix}{ss}{suffix}\n")` – Gino Mempin Sep 11 '21 at 04:37

Andrew Clark · Answer 2 · 2011-10-28T20:52:14.577

5

You can make changes to the file without opening multiple files by using fileinput with inplace=1:

import fileinput
for line in fileinput.input('test.txt', inplace=1):
    print '{0}{1}{2}'.format('111', line.rstrip('\n'), '222')

edited Oct 28 '11 at 20:52

answered Oct 28 '11 at 18:57

Andrew Clark

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On Python 2.5 or below replace the print line with `print '%s%s%s' % ('111', line[:-1], '222')` – Andrew Clark Oct 28 '11 at 18:59
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-1: NEVER use `line[:-1]`, in case the last line is not terminated. Use `line.rstrip('\n')` – John Machin Oct 28 '11 at 20:42

score 0 · Answer 3 · answered Oct 28 '11 at 18:52

0

Assuming you have read the file using readlines() in a list you can do

value1 = "" # appended at first
value2 = "" # appended at last
data = file.readlines()
data = [ ( value1 + str.rstrip('\n') + value2 + "\n" ) for str in data ]

and then write data back to the file....

answered Oct 28 '11 at 18:52

user671805

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1

This has to hold the entire file in memory, as opposed to Steven Rumbalski's answer. – zekel Oct 28 '11 at 19:02

score -1 · Answer 4 · answered Oct 28 '11 at 18:53

-1

f1o = open("input.txt", "r")
f2o = open("output.txt", "w")

for line in f1o:
    f2o.write("111%s222\n" % line.replace("\n"))

f1o.close()
f2o.close()

answered Oct 28 '11 at 18:53

lifeisstillgood

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`replace` takes two arguments. – Steven Rumbalski Oct 28 '11 at 18:57

How to write to beginning and end of every line in a text file?

4 Answers4