finding indices in a sequence of parentheses

[Steven Bethard]

I have a list of strings that looks something like:

lst = ['0', '0', '(*)', 'O', '(*', '*', '(*', '*))', '((*', '*)', '*)']

The parentheses in the labels indicate where an "annotation" starts and 
ends.  So for example, the label '(*)' at index 2 of the list means that 
I have an annotation at (2, 2), and the labels '(*', '*', '(*', '*))' at 
indices 4 through 7 mean that I have an annotation at (4, 7) and an 
annotation at (6, 7).

I'd like to determine all indices at which I have an annotation.  So for 
the data above, I want the indices:

     (2, 2), (4, 7), (6, 7), (8, 9) and (8, 10)

Here's what I'm doing now:

py> def indices(lst):
...     stack = []
...     for i, s in enumerate(lst):
...         if s == 'O':
...             continue
...         stack.extend([i]*s.count('('))
...         if '*' in s and not stack:
...             raise Exception('No start for %r at %i' % (s, i))
...         for _ in range(s.count(')')):
...             try:
...                 yield stack.pop(), i
...             except IndexError:
...                 raise Exception('No start for %r at %i' % (s, i))
...     if stack:
...         raise Exception('No ends for starts at %r' % stack)
...
py> list(indices(['0', '0', '(*)', 'O', '(*', '*', '(*', '*))', '((*', 
'*)', '*)', '0']))
[(2, 2), (6, 7), (4, 7), (8, 9), (8, 10)]

I think that works right, but I'm not certain.  So two questions:

(1) Can anyone see anything wrong with the code above? and
(2) Does anyone see an easier/clearer/simpler[1] way of doing this?

Thanks,

STeVe

[1] Yes, I know easier/clearer/simpler are subjective terms.  It's okay, 
I'm only looking for opinions here anyway. =)