import csv
import fileinput
import sys

reader = csv.reader(fileinput.input(inplace=True))  # modify input files inplace
writer = csv.writer(sys.stdout)  # fileinput redirects stdout to input file
                                                # after input file has been copied to a temporary file
for row in reader:
     row += [row[-1]]  # duplicate last column
     writer.writerow(row)