How to transform a list into a CSV file with N items per row?

Question

I want to create a new CSV file with 3 items per row. My source file looks like (there are no new lines / line breaks):

Answer 1

You mentioned:

My source file looks like (there are no new lines / line breaks):

12123, 1324, 232324, 243443, 234, 2345 2334, 2445, 22355, 222234, 2345

So this reads one long row of a CSV, then writes it as groups of three per line:

import csv

with open('test.csv',newline='') as f:
    reader = csv.reader(f)
    line = next(reader) # Read the one long line

with open('test2.csv', 'w', newline='') as csvfile:
    writer = csv.writer(csvfile)
    for i in range(0,len(line),3): # step by threes.
        writer.writerow(line[i:i+3])

Note that correct use of the csv module requires the files to be opened with newline='' in Python 3 ('rb' or 'wb' in Python 2).