Python list index out of range on return value of split

Question

I'm writing a simple script that is trying to extract the first element from the second column of a .txt input file.

import sys

if (len(sys.argv) > 1):
    f = open(sys.argv[1], "r");
    print "file opened";

line = [];

for line in f:
    line = line.strip("\n ' '")
    line = line.split(",") 
    print line[1]

f.close();

My input file looks like this:

Client 192.168.1.13 said ``ACC: d0bb38f18da536aff7b455264eba2f1e35dd976f,389182.567,-0.042,-0.893,0.333''
Client 192.168.1.13 said ``ACC: d0bb38f18da536aff7b455264eba2f1e35dd976f,389182.590,-0.036,-0.905,0.273''
Client 192.168.1.13 said ``ACC: d0bb38f18da536aff7b455264eba2f1e35dd976f,389182.611,-0.046,-0.948,0.204''
Client 192.168.1.13 said ``ACC: d0bb38f18da536aff7b455264eba2f1e35dd976f,389182.631,-0.074,-0.978,0.170''
Client 192.168.1.13 said ``ACC: d0bb38f18da536aff7b455264eba2f1e35dd976f,389182.654,-0.100,-1.006,0.171''

I want my delimiter to be a comma. When I print the length of the line out, I'm getting 5 elements (as expected). However, whenever I try to index the list to extract the data (i.e., when I call print line[1]), I keep getting the following error:

file opened
Traceback (most recent call last):
  File "stats.py", line 13, in <module>
    print line[1]
IndexError: list index out of range

I don't understand why it's out of range when clearly it isn't.

Answer 1

I would guess you have a blank line somewhere in your file. If it runs through the data and then generates the exception the blank line will be at the end of your file.

Please insert

print len(line), line

before your

print line[1]

as a check to verify if this is the case.

You can always use this construct to test for blank lines and only process/print non-blank lines:

for line in f:
    line = line.strip()
    if line:
       # process/print line further

Answer 2

When you are working with list and trying to get value at particular index, it is always safe to see in index is in the range

if len(list_of_elements) > index: 
   print list_of_elements[index]

See:

>>> list_of_elements = [1, 2, 3, 4]
>>> len(list_of_elements)
4
>>> list_of_elements[1]
2
>>> list_of_elements[4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range
>>> 

Now you have to find out why your list did not contain as many elements as you expected

Solution:

import sys

if (len(sys.argv) > 1):
    f = open(sys.argv[1], "r")
    print "file opened"

for line in f:
    line = line.strip().strip('\n')
    # Ensure that you are not working on empty line
    if line:
        data = line.split(",") 
    # Ensure that index is not out of range
    if len(data) > 1: print data[1]

f.close()