Updating values in a dictionary

[Terry Reedy]

On 5/16/2010 1:36 PM, Thomas wrote:
> Greetings
>
> I am having a darn awful time trying to update a matrix:
>
> row = dict([(x,0) for x in range(3)])
> matrix = dict([(x,row) for x in range(-3,4,1)])
>
> matrix[2][1] += 1
> matrix[-1][2] += 1

Dicts are fine for sparse matrixes, but when filled in, a list of lists 
is perhaps easier and more efficient. And you can iterate and be 
guaranteed to get the sublists in the expected order.