Explain: x0 = (x//3)*3

[davidm]

Hi,
I'm following this youtube code for a sudoku solver using python.
In the following piece

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def possible(y,x,n):     global grid     for i in range(0,9):         if grid[y][i] == n:             return False     for i in range(0,9):         if grid[i][x] == n:             return False  """ [b]don't understand the following 2 lines[/b] """     x0 = (x//3)*3     y0 = (y//3)*3       for i in range(0,3):         for j in range(0,3):             if grid[y0+i][x0+j] == n :                 return False     return True

Could someone explain the 2 I don't understand. I understand from the context that it's connected to checking a 3 by 3 square, but I can't find an explanation for this code.
Thanks

[deanhystad]

// integer division, so (x // 3) * 3 will round down to a multiple of 3. If x was 5, x //3 would be 1 (not 1.66), and (x // 3) * 3 is 3. It looks like this is used to force x and y to be on a 3 x 3 grid.

[davidm]

Thanks Dean,
Searched for Python symbol "//" but wasn't successful

[Yoriz]

floor division
3.1.1. Numbers>Division