Вы получаете сообщение об ошибке из-за пустой строки
import csv
import operator
result = []
with open(filename) as infile:
reader = csv.reader(infile,delimiter=',')
for line in reader:
if line: #Check if line is empty
result.append(line)
print(sorted(result,key=operator.itemgetter(1)))
или используйте filter
with open(filename) as infile:
reader = csv.reader(infile,delimiter=',')
print( sorted(filter(None, reader),key=operator.itemgetter(1)) )