Game of Life (neighbors)

[pawlo392]

I found something like this:

  for x in range(S):
    for y in range(S):
      
      total = (tablica[x, (y-1)%S] + tablica[x, (y+1)%S] + 
               tablica[(x-1)%S, y] + tablica[(x+1)%S, y] + 
               tablica[(x-1)%S, (y-1)%S] + tablica[(x-1)%S, (y+1)%S] + 
               tablica[(x+1)%S, (y-1)%S] + tablica[(x+1)%S, (y+1)%S])

Where S-size.
Could You tell my, why we "check" modulo for each coordinate?