Question

Hi I have a csv file with names and surnames and empty username and password columns.
How can I use python csv to write to the columns 3 and 4 in each row, just appending to it, not overwriting anything.

Answer 1

The csv module doesn’t do that, you’d have to write it out to a separate file then overwrite the old file with the new one, or read the whole file into memory and then write over it.

I’d recommend the first option:

from csv import writer as csvwriter, reader as cvsreader
from os import rename # add ', remove' on Windows

with open(infilename) as infile:
    csvr = csvreader(infile)
    with open(outfilename, 'wb') as outfile:
        csvw = csvwriter(outfile)
        for row in csvr:
            # do whatever to get the username / password
            # for this row here
            row.append(username)
            row.append(password)
            csvw.writerow(row)
            # or 'csvw.writerow(row + [username, password])' if you want one line

# only on Windows
# remove(infilename) 
rename(outfilename, infilename)