IndexError: list index out of range Python 2.7.x

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.

jonrsharpe · Accepted Answer · 2013-12-28 22:47:59Z

4

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]

edited Dec 28, 2013 at 22:47

answered Dec 28, 2013 at 22:41

jonrsharpe

123k31 gold badges278 silver badges488 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

MCP_infiltrator Over a year ago

works great but I am instructed to use a and operator unless it's a book typo

kirbyfan64sos · Accepted Answer · 2013-12-28 22:40:55Z

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.

answered Dec 28, 2013 at 22:40

kirbyfan64sos

10.8k6 gold badges58 silver badges79 bronze badges

1 Comment

MCP_infiltrator Over a year ago

works great but I am instructed to use a and operator unless it is a typo in the book

Collectives™ on Stack Overflow

IndexError: list index out of range Python 2.7.x

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related