finding indices in a sequence of parentheses

[Peter Otten]

tiissa wrote:

> Steven Bethard wrote:
>> (2) Does anyone see an easier/clearer/simpler[1] way of doing this?
> 
> I'd personnally extract the parenthesis then zip the lists of indices.
> In short:
> 
>   >>> def indices(mylist):
>   ...     lopen=reduce(list.__add__, [[i]*s.count('(') for i,s in
> enumerate(mylist)],[])
>   ...     lclose=reduce(list.__add__, [[i]*s.count(')') for i,s in
> enumerate(mylist)],[])
>   ...     return zip(lopen,lclose)
>   ...
>   >>> indices(lst)
>   [(2, 2), (4, 7), (6, 7), (8, 9), (8, 10)]
>   >>>
> 
> Before returning, you can check if the lists have same size and if the
> '(' has lower or equal index than ')' in each of these couples. If not
> you can raise the appropriate exception.
> 
> Disclaimer: not tested further than example above (but confident).

Not tested but confident should be an oxymoron for a programmer. Some
examples:

lst: ['(', '(', ')', ')']
hettinger [(1, 2), (0, 3)]
bethard [(1, 2), (0, 3)]
tiissa [(0, 2), (1, 3)] oops (or am I just spoilt by the XML spec?)

lst: ['(', ')(', ')']
hettinger [(0, 1), (1, 2)]
bethard [(1, 1), (0, 2)] oops
tiissa [(0, 1), (1, 2)]

So far Raymond's solution is my favourite...

Peter