default value for list access?

[Bo Peng]

Dear list,
My program needs to do calculation based on a giving data structure 
(like a sparse matrix) with  lots of missing values (invalid 
indices/keys of lists/dictionaries).

The programing is difficult in that I have to use a try...except block 
for every item access. I have written a function

def getItem(item, idx, default):
  try:
    return item[idx]
  except:
    return default
Then I will have to write a[1]['a'][4] as
getItem( getItem( getItem(a,1,{}), 'a', []), 4, 0)
Is there any way to automatically return 0 when any exception is raised 
for such data acceses? (automatic wrapping a[...] as
 try:
   a[...]
 except:
   0
)

Many thanks in advance.
Bo
--
http://mail.python.org/mailman/listinfo/python-list