krosecsv

import csv

newskulist = []
with open('old.csv', newline='') as oldsku:
	reader = csv.reader(nusku, newline='')
	for row in reader:
		#check rownum
		newskulist.append(row[3])



with open('sku.csv', newline='') as nusku:
	writer = csv.writer(nusku, dialect='excel' newline='')

	for row in writer:
		if row[3] in newskulist:
			row[3] = ''