[Tutor] Creating a two dimension set

[Phil]

As an example, if I wanted to create a two dimension list I would write:

num_rows = 9
num_cols = 9

self.solution = [[None] * num_cols for _ in range(num_rows)]

In my current creation I need a two dimension set and so I have used, 
again for example:

result = set(self.solution[row][col]) - 3

However, my code has grown and I find that I'm making mistakes and it 
would be much simpler if I'd created a two dimension set in the first 
place rather that converting the list to a set every time I need to 
access it.

I could, I suppose, use two for loops to create and initialise the set 
but there must be a simpler and less tedious way.

I have very poor Internet access at the moment and searching for an 
answer hasn't been fruitful due to frequent disconnections. All that 
I've gained is a headache.

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Regards,
Phil