pandas dataframe to_csv writes blank line after each line

Question

When I write a data frame to a csv if I use the "with open", I get a blank line after each line in the csv file:

df = pd.DataFrame(data=np.random.randint(0, 100, (4, 5)), columns=list('ABCDE'))
with open('test.csv', 'a') as f:
    df.to_csv(f, header=False)

If I simply do:

df.to_csv('test.csv', header=False)

There is no blank line! What am I doing wrong?

Your second option is the correct way to use `.to_csv()` with pandas. — Sebastien D, Jul 08 '19 at 15:02
If I use with open, I can check if the file exists or not and If not write the header. If yes, I don't write it. and all this in the same line without a lot of hassle! — Laleh, Jul 08 '19 at 15:03
Refer to this post : `How to add pandas data to an existing csv file?` - https://stackoverflow.com/questions/17530542/how-to-add-pandas-data-to-an-existing-csv-file — Sebastien D, Jul 08 '19 at 15:06
I'm confused. How either of the options could produce the blank line after **each** line? — Quang Hoang, Jul 08 '19 at 15:10

rbcvl · Accepted Answer · 2019-07-08T15:15:34.093

10

By default, the newline of :

with open('test.csv', 'a') as f

is \r\n

The newline in to_csv() is \n.

You can try with :

with open('test.csv', 'a', newline = '\n') as f

edited Jul 08 '19 at 15:15

answered Jul 08 '19 at 15:11

rbcvl

If I open the file to write, It doesn't append. It just rewrites – Laleh Jul 08 '19 at 15:14
The `a` parameter for appending instead `w` for writing. Apologize. – rbcvl Jul 08 '19 at 15:17

1 Answers1