Error in writing a list to a CSV column in python

Question

I want to write a list to the third column of a csv file.

list = ['cat', 'dog', 'duck', ..., 'goat']

writer = csv.writer(f)
for val in list:
    writer.writerow([val])

However the output I get always has one row empty in between as follows.

cat

dog

duck

...

goat

I want to know how to make it correct as well as to have the list in the third column of csv.

If you want the values in the third column, then what would the first two columns be? — Anand S Kumar, Aug 25 '17 at 05:19
Oh sorry, its a typo. its a list. I corrected it. I want to have first two columns to have numbers starting from zero. — , Aug 25 '17 at 05:21
The issue is that an extra carriage return is added in between the lines causing it to be - `cat\r\r\ndog....` . — Anand S Kumar, Aug 25 '17 at 06:14

Dewald Abrie · Accepted Answer · 2017-08-25T06:05:04.463

1

With Blanks

You can easily add empty columns by adding "None" entries in the list argument to writerow(). A fully working example follows:

import csv
import tempfile

list = ['cat', 'dog', 'duck', 'goat']

name = None
with tempfile.NamedTemporaryFile('w', delete=False) as f:
    writer = csv.writer(f)
    for val in list:
        writer.writerow([None, None, val])

    name = f.name

with open(name, 'r') as f:
    contents = f.read()
    print(contents)

The result is:

,,cat
,,dog
,,duck
,,goat

With Numbers

In order to have numbers starting from zero instead of blanks you can modify like so:

import csv
import tempfile

list = ['cat', 'dog', 'duck', 'goat']

name = None
with tempfile.NamedTemporaryFile('w', delete=False) as f:
    writer = csv.writer(f)
    pos = 0
    for val in list:
        writer.writerow([str(pos), str(pos+1), val])
        pos += 2

    name = f.name

with open(name, 'r') as f:
    contents = f.read()
    print(contents)
    print(dir(f))

This results in the following:

0,1,cat
2,3,dog
4,5,duck
6,7,goat

edited Aug 25 '17 at 06:05

answered Aug 25 '17 at 05:59

Dewald Abrie

1,183
7
19

Did you try your code with a normal file? Does it still correctly write out the results without extra newline? – Anand S Kumar Aug 25 '17 at 06:07
Yes, I tried it and I don't get any extra newlines. – Dewald Abrie Aug 25 '17 at 06:20
Excellent, Good answer. However, I still get the extra new line prob. – Aug 25 '17 at 06:20
To use a regular file, just replace "tempfile.NamedTemporaryFile('w', delete=False)" with "open('temp.csv', 'w')". – Dewald Abrie Aug 25 '17 at 06:20
You might not be trying in windows. or you might not be using python 3 – Anand S Kumar Aug 25 '17 at 06:21
@David Checkout the duplicate bug, for details on the new line prob – Anand S Kumar Aug 25 '17 at 06:22
To avoid the extra line breaks (probably you're using Windows?), see this post: https://stackoverflow.com/questions/3191528/csv-in-python-adding-an-extra-carriage-return – Dewald Abrie Aug 25 '17 at 06:23
Thanks a lot all. It solved. I simply used newline='' in file open as given in that question. with open('output.csv','w',newline='') as f: writer=csv.writer(f) writer.writerow(mystuff) ... – Aug 25 '17 at 06:28

Error in writing a list to a CSV column in python

1 Answers1

With Blanks

With Numbers