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

A four-line solution without the csv module:

with open('oneline_numbers.csv') as fobj_in, open('three_numbers.csv', 'w') as fobj_out:
    numbers = iter(entry.strip() for entry in next((fobj_in)).split(','))
    for line in zip(*[numbers] * 3):
        fobj_out.write(', '.join(line) + '\n')