Unexpected changes to data need to be guarded against, and data can be accompanied by a checksum to help detect errors. A checksum is a computation that is performed over all the data it protects, and the computed value is stored with the data. Upon reading or transmitting the data, the data checksum is recomputed and compared to the stored value; if they differ, then this tells you that the data has changed.

In this section you will be writing a program to recompute and verify a simple checksum for data files. The data files consist of lines of text followed by the sentinel END on a line by itself. The line following the END has a checksum value for the data, which is an integer value greater than or equal to zero.

The checksum is the sum of the lengths of the lines comprising the data. The END sentinel and the checksum itself are not added to the checksum. For example, here is one possible data file:

foo

garble

blarg

END

14

The checksum is 14 because the length of "foo" plus the length of "garble" plus the length of "blarg" equals 14. If the checksum were a value other than 14, then your program would indicate a checksum error.

Start with the following code:

SENTINEL = 'END'

chksum = AAA

while BBB:

line = input()

if CCC: DDD

chksum = EEE oldchksum = FFF

if GGG:

print('checksum error')

The code is run by typing

spy3 section3.py < datafile

1) What should AAA be replaced with?

0, 1 ,'14' ,14

2) What should BBB be replaced with?

input() != SENTINEL , input() != 'END' , True ,0 , False.

3) What should CCC be replaced with?

line == 'SENTINEL' , line = 'END' ,line == 'END'

, line = SENTINEL , line == SENTINEL

4) What should DDD be replaced with?

continue , Nothing , break , line = input()

5) What should EEE be replaced with?

chksum len(line)

chksum + int(line)

chksum + len(line)

chksum + line

chksum int(line)

6) What should FFF be replaced with?

int(input())

int(input)

input()

line

int(line)

7) What should GGG be replaced with?

chksum = oldchksum

chksum or oldchksum

chksum != oldchksum

chksum == oldchksum