How can I replace first line of a csv with a header using Python?

Question

I'm trying to replace the first line of a csv input file with a header. The first line is blank, 0. See image below.

I want the blank and 0 to be "ID" and "sil_score" respectively. See below:

But I keep getting this:

import csv
r = csv.reader(open('C:/Users/Desktop/Geosill/attempt1.csv')) 
lines = list(r)

lines[1][0] = 'ID'
lines[2][0] = 'sil_score'


writer = csv.writer(open('C:/Users/Desktop/Geosill/attempt3.csv', 'w'))
writer.writerows(lines)

score 0 · Answer 1 · answered Jun 09 '20 at 21:55

If you're looking to edit the first two lines of the .csv you'll have to change how you access the lines list.

You'll need to use

lines[0][0]='ID'
lines[0][1]='sil_score'

instead.

The output seems odd though, could be something weird with the csv import. Try opening the files in a text editor, might be easier to see what's going on.

score 0 · Accepted Answer · answered Jun 09 '20 at 21:58

This will do it. newline='' should be used to fix the blank line issue you are seeing as well.

import csv

with open('input.csv',newline='') as f:
    r = csv.reader(f)
    lines = list(r)

lines[0] = ['ID','sil_score']

with open('output.csv','w',newline='') as f:
    w = csv.writer(f)
    w.writerows(lines)

Krishnan Shankar · Answer 3 · 2020-06-10T22:01:12.873

-1

You can do this without using csv.writer. Try this:

with open('C:/Users/Desktop/Geosill/attempt1.csv', "r") as infile:
    lines = infile.readlines().rstrip().split(",")
lines[0] = ["ID", "sil_score"]
with open('C:/Users/Desktop/Geosill/attempt1.csv', "w") as outfile:
    for line in lines:
        outfile.write(",".join(line))

Hope this helps!

edited Jun 10 '20 at 22:01

answered Jun 09 '20 at 21:49

Krishnan Shankar

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No, you need writer to write a lists to a csv. Check your results. `lines` is a list of lists. – Mark Tolonen Jun 09 '20 at 21:59
Yes, and I am joining the list elements with a comma. I don't believe we NEED CSV writer. I just use the regular file writer. – Krishnan Shankar Jun 12 '20 at 14:40
Until you have commas and quotes in the content and then it breaks. – Mark Tolonen Jun 12 '20 at 16:29
Yes, agreed. But since @bkGeog only wants to change the headers to text, I think it will be fine. – Krishnan Shankar Jun 12 '20 at 16:32
For this user, not the next one. – Mark Tolonen Jun 12 '20 at 16:58

How can I replace first line of a csv with a header using Python?

3 Answers3