Row class should support negative indexes and slice syntax

[GoogleCodeExporter]

What steps will reproduce the problem?

import arff
for row in arff.load('example.arff'):
    print row[-1]


Where this is the example file:
@relation diabetics_data
@attribute hair_color {blonde, black, blue}
@attribute age real
@attribute patno integer
@data
blonde, 17.2, 1
blue, 27.2, 2
blue, 18.2, 3







What is the expected output? What do you see instead?

Should print:

1
2
3

But this is happening:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    y = row[-1]
  File "/usr/local/lib/python2.7/dist-packages/arff/__init__.py", line 105, in __getitem__
    return self._data[key]
KeyError: -1

What version of the product are you using? On what operating system?

arff librry version 0.9
python 2.7
ubuntu 12.04

Original issue reported on code.google.com by [email protected] on 20 Sep 2012 at 5:32