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

Here's a solution but it's a bit long. Basically I would write all the values in the csv to a list, then remove three value from the list and write to the csv until there's no values left.

import csv

# just an example csv
with open('example.csv', 'w') as csvfile:
    # create example csv with a single row of numbers 0-19
    spamwriter = csv.writer(csvfile)
    spamwriter.writerow([i for i in range(20)])

# open file for reading, append values to list
l = []
with open('example.csv') as csvfile:
    # read the example file into a list
    reader = csv.reader(csvfile)
    for row in reader:
        for val in row:
            l.append(val)


# write to the original file with 3 values per line
with open('example.csv', 'w') as csvfile:
    spamwriter = csv.writer(csvfile)
    while l:
        try:
            # write to file 3 values at a time
            spamwriter.writerow(l[:3])
            l = l[3:]
        except:
            # add last bit of file, if file doesn't devide evenly by 3
            spamwriter.writerow(l)
            break

I'd recommend checking out Pandas I find it a lot easier to manipulate csvs with it, but it's not in the standard library.