Append in each line of a .txt file a specific string using Python

Question

I have a .txt file with has the following format:

/Users/my_user/folder1/myfile.dat
/Users/my_user/folder2/myfile.dat
/Users/my_user/folder3/myfile.dat
.
.
.
so on

I want to append in the end of each line another folder path in order to make it look like this:

/Users/my_user/folder1/myfile.dat,/Users/my_user/folder1/otherfile.dat
/Users/my_user/folder2/myfile.dat,/Users/my_user/folder1/otherfile.dat
/Users/my_user/folder3/myfile.dat,/Users/my_user/folder1/otherfile.dat
.
.
.
so on

Till now I have tried in a loop:

with open("test.txt", "a") as myfile:
    myfile.write("append text")

But i only writes at the end of the file.

Avinash Raj · Accepted Answer · 2015-03-04 13:21:10Z

2

You could use re.sub function.

To append at the start of each line.

with open("test.txt", "r") as myfile:
    fil = myfile.read().rstrip('\n')
with open("test.txt", "w") as f:
    f.write(re.sub(r'(?m)^', r'append text', fil))

To append at the end of each line.

with open("test.txt", "r") as myfile:
    fil = myfile.read().rstrip('\n')
with open("test.txt", "w") as f:
    f.write(re.sub(r'(?m)$', r'append text', fil))

edited Mar 4, 2015 at 13:21

answered Mar 4, 2015 at 12:58

Avinash Raj

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4 Comments

azal Over a year ago

I tried it and it writes in front of the already existing text in the corresponding line. How can it write at the end of it?

Avinash Raj Over a year ago

you the one asks for appending at the start of each line.

azal Over a year ago

oops yes. I thought it was obvious from the example folders i posted but anyway I edited my post since it was not clear. How can i do it after the end of the line anyhow?

azal Over a year ago

even with the rstrip('\n') it writes at the beginning

Bhargav Rao · Accepted Answer · 2015-03-04 13:10:17Z

0

You can try to do something like this:

with open(file_name, 'r') as f:
    file_lines = [''.join([x.strip(), string_to_add, '\n']) for x in f.readlines()]

with open(file_name, 'w') as f:
    f.writelines(file_lines)

edited Mar 4, 2015 at 13:10

Bhargav Rao

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answered Mar 4, 2015 at 12:58

tema

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