How to avoid the last comma while writing an integer array into a text file in python

Question

I need to write an array of integers into a text file, but the formatted solution is adding the comma after each item and I'd like to avoid the last one.

The code looks like this:

        with open(name, 'a+') as f:
           line = ['FOO ', description, '|Bar|']
           f.writelines(line)
           f.writelines("%d," % item for item in values)
           f.writelines('\n')

Each line starts with a small description of what the array to follow contains, and then a list of integers. New lines are added in the loop as they become available.

The output I get looks something like this:

FOO description|Bar|274,549,549,824,824,824,824,824,794,765,765,736,736,736,736,736,

And I would like to have it look like this, without the last comma:

FOO description|Bar|274,549,549,824,824,824,824,824,794,765,765,736,736,736,736,736

I was unable to find a solution that would work with the writelines() and I need to avoid lengthy processing in additional loops.

convert the string to list by mapping or something then do: obj.rstrip(',') after that write it to the text file as it'll finally need a textfile (string) to write to a file! — Ubdus Samad, Aug 28 '17 at 13:05
@Jon, that's an answer. If you don't want to write it down, I'll take the points. :-) — lucid_dreamer, Aug 28 '17 at 13:06

score 9 · Accepted Answer · answered Aug 28 '17 at 13:06

9

Use join:

f.writelines(",".join(map(str,values)))

Note that values is first mapped to a list of strings, instead of numbers, with map.

answered Aug 28 '17 at 13:06

trincot

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This would work, but I need to keep numbers without converting them to strings – TeilaRei Aug 28 '17 at 14:42
Content written to a file is always written as a string, you convert it to string yourself with the `%` operator, and the desired output you have at the end of your question is a string. So I must ask: What do you mean? – trincot Aug 28 '17 at 14:44
That is a good point, for some reason I've been unaware of that transformation. I guess I was looking for a way to actually preserve the original type of the data, but it doesn't seem to be possible with the text file. – TeilaRei Aug 28 '17 at 14:51

score 1 · Answer 2 · answered Aug 28 '17 at 13:08

1

You can slice it with using below example. It will always delete last character.

line = ['FOO ', description, '|Bar|']
line = line[:-1]
f.writelines(line)

answered Aug 28 '17 at 13:08

Gokturk

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score 1 · Answer 3 · answered Aug 28 '17 at 14:49

1

Slicing is the best approach and works well for every situation atleast in your case.

    f.writelines(line[:-1])

answered Aug 28 '17 at 14:49

Chetan_Vasudevan

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score 0 · Answer 4 · answered Aug 28 '17 at 13:17

0

You can use print function here.

print(*values,sep=',',file=f)

If you are using python2 please import print function.

from __future__ import print_function

answered Aug 28 '17 at 13:17

Abhijith Asokan

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How to avoid the last comma while writing an integer array into a text file in python

4 Answers4