[Tutor] Creating a two dimension set

[Cameron Simpson]

On 01Nov2021 17:18, Phil <phillor9 at gmail.com> wrote:
>Problem solved. Actually, the solution had nothing to do with my 
>question. Too much looking and not enough seeing. The following works:
>
>num_rows = 2
>num_cols = 2
>
>grid = [[str] * num_cols for _ in range(num_rows)] # I changed None to 
>str but I don't thing it matters.

Bare "str" isn't a good thing. Use None, it is the idiomatic Python 
value for "no value here" (there's a value, but it isn't in the expected 
range). Bare "str" means you've filled your lists with references to the 
str type. Kind of weird.

>for row in range(2):
>    for col in range(2):
>        grid[row][col] = set({'1', '2', '3', '4', '5', '6', '7', '8', '9'})

You don't need to say "set({....})". The "{.....}" stuff is already a 
set. Except for "{}" which is an empty dict - for an empty set you need 
to say "set()".

I wouldn't use strings. If you're doing Sudoku don't you want to do 
arithmetic to check the sum? May as well make a set of ints:

    {1, 2, 3, 4, 5, 6, 7, 8, 9}

>grid[0][0].remove('3')

Yes. Of course, using ints would be grid[0][0][.remove(3). Adjust to 
suit.

If you wanted to simplify the setup you could fill the grid with empty 
sets instead and have it represent rejected values instead of potential 
values. Of course you'd have to turn some other logic upside down.

Cheers,
Cameron Simpson <cs at cskk.id.au>