Stride tricks for Sudoku

The ndarray class has a strides field, which is a tuple indicating the number of bytes to step in each dimension when going through an array. Let's apply some stride tricks to the problem of splitting a Sudoku puzzle to the 3 by 3 squares of which it is composed.

Note

Explaining the Sudoku rules is outside the scope of this book. For more information see http://en.wikipedia.org/wiki/Sudoku.

How to do it...

1. Define the Sudoku puzzle array

   Let's define the Sudoku puzzle array. This one is filled with the contents of an actual, solved Sudoku puzzle:

   sudoku = numpy.array([
       [2, 8, 7, 1, 6, 5, 9, 4, 3],
       [9, 5, 4, 7, 3, 2, 1, 6, 8],
       [6, 1, 3, 8, 4, 9, 7, 5, 2],
       [8, 7, 9, 6, 5, 1, 2, 3, 4],
       [4, 2, 1, 3, 9, 8, 6, 7, 5],
       [3, 6, 5, 4, 2, 7, 8, 9, 1],
       [1, 9, 8, 5, 7, 3, 4, 2, 6],
       [5, 4, 2, 9, 1, 6, 3, 8, 7],
       [7, 3, 6, 2, 8, 4, 5, 1, 9]
       ])

2. Calculate the strides. The itemsize field of ndarray gives us the number of bytes in an array. Using the...