IndexError：列表索引超出Python 2.7.x范围

Question

I am going through chapter 8 of Python for Informatics and have been asked for an exercise to rewrite the following function:

fhand = open('mbox-short.txt')
count = 0
for line in fhand:
    words = line.split()
    #print 'Debug:', words
    if len(words) == 0:
        continue
    if words[0] != 'From':
        continue
    print words[2]

I was asked to rewrite it using a single compound if statement, so I wrote the following:

fhand = open('mbox-short.txt')
#count = 0 <-- not even sure why this is in the orginal
for line in fhand:
    words = line.split()
    print 'Debug:', words
    if len(words) == 0 and words[0] != 'From':
        continue
    print words[2]

The first function works just fine, but the second gives me the following error:

Traceback (most recent call last):
  File "ch8.py", line 258, in <module>
    print words[2]
IndexError: list index out of range

I do not understand why what I wrote is returning the error, as far as I can tell I am doing the same exact thing, but apparently I am wrong, I just don't understand why. Maybe there is a subtle issue that I am just not picking up on.

Thank you,

UPDATE

Instructions 'use a compound logical expression using the and logical operator with a single if statement.

Answer 1

In the original code

    if len(words) == 0:
        continue
    if words[0] != 'From':
        continue

You reach continue in either case. Therefore the single line version should be

if len(words) == 0 or words[0] != 'From':
                #  ^ or, not and
    continue

If you need to use and , more refactoring is needed, switching the print and (now-implicit) continue and reversing the tests:

if len(words) > 0 and words[0] == 'From':
    print words[2]

Answer 2

fhand = open('mbox-short.txt')
for line in fhand:
    words = line.split()
    print 'Debug:', words
    if len(words) == 0 or words[0] != 'From':
        continue
    print words[2]

Change and to or .