Python: append split list is empty

Question

My objective or output I'm looking for is to append to input txt file the first part of all lines of existing input file. As an example:

Input:
line_item1 string1
line_item2 string2
line_item3 string3

Output:
line_item1 string1
line_item2 string2
line_item3 string3
line_item1   # append
line_item2   # append
line_item3   # append

The code I have created does not output anything:

portionA = []
with open('output outfile.txt', "a+") as f:
    for line in f.readlines():
        parts = line.strip().split("\t", 1)
        portionA = parts[0]
        portionB = parts[1]
        portionA.append(line)
        f.write('{}\n'.format(''.join(portionA)))

This is fairly unclear. Can you provide some actual examples? What do you mean by 'selected lines'? — Goodies, Feb 11 '16 at 16:51
I see you want to append the same lines at end. Deleted my answer — Obsidian, Feb 11 '16 at 16:53
@user1739581 On second thought, it does look my instincts were right. Have undeleted and updated my answer. Please take a look — Obsidian, Feb 11 '16 at 17:11

Martín Muñoz del Río · Accepted Answer · 2016-02-11T17:24:00.400

1

You can try:

with open('output outfile.txt', "a+") as f:
    for line in f.readlines():
        parts = line.strip().split("\t")
        f.write('{}\n'.format(parts[0]))

edited Feb 11 '16 at 17:24

answered Feb 11 '16 at 16:54

Martín Muñoz del Río

1,958
11
14

score 0 · Answer 2 · edited May 23 '17 at 11:44

0

You should use 'r+' instead of 'a+'.

``r+''  Open for reading and writing.  The stream is positioned at the
         beginning of the file.

Why a+ doesn't work is discussed here

I can't correct the indents on your code for the f.write so here's the corrected snippet (Note the join with \n instead of empty string)

writeList= []
with open('outfile.txt', "r+") as f:
    for line in f:
        parts = line.strip().split("\t", 1)
        portionA = parts[0]
        portionB = parts[1]
        writeList.append(line)
    f.write('{}\n'.format('\n'.join(writeList)))

edited May 23 '17 at 11:44

Community

1
1

answered Feb 11 '16 at 16:51

Obsidian

515
3
10

1

This would be better as a comment. – Goodies Feb 11 '16 at 16:52

Python: append split list is empty

2 Answers2