mask.py

#!/usr/bin/env python
import sys
import csv

# tabbed file tabs.txt:
#one	two	three	four
# cmd:
#cat tabs.txt | ./mask.py 2 CUSTOMER_

POS = int(sys.argv[1])
LABEL = sys.argv[2]

def checksum256(start):
  """ checksum """
  return reduce(lambda x, y:x+y, map(ord, start)) % 256

CF = csv.reader(sys.stdin, delimiter='\t')
for row in CF:
  row[POS] = LABEL + str(checksum256(row[1])).zfill(3)
  print '\t'.join(row)