though, the best case is to preallocate, which I think you can use `indptr` for:

`nnz = [indptr[i+1] - indptr[i] for i in range(0, len(indptr) - 1)]`

...which should be the final length of `data` and `indices`.

@ElBrogrammer or @Jorge-C, are either of you familiar with a numpy method that would do the above list comp?