outfname = 'csv_stripped.csv'
cols = ['col1', 'col2', 'col3']
with open(infname) as inf:
    with open(outfname, 'w+') as outf:
        reader = csv.DictReader(inf)
writer = csv.DictWriter(outf, cols, extrasaction='ignore')
writer.writeheader()
for line in reader:
    writer.writerow(line)
Использование Python для разбора CSV-файла размером 12 ГБ