Checking whether list element exists

[Rehceb Rotkiv]

> In general case it won't work, because lists accept negative indexes:
> http://docs.python.org/lib/typesseq.html, 3rd note.

Yes, I know! I _want_ the "3rd last list element", i.e. list[-3]. But it 
may be that the list does not have 3 elements. In this case, list[-3] 
will throw an error, cf.:

>>> arr = ['a','b','c']
>>> print arr[-3]
a
>>> print arr[-4]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
IndexError: list index out of range
>>> 

I thought maybe I could catch the error with try...except so that I do 
not need the if-test, but I don't know whether this is proper usage of 
the try...except structure.