title: Iterate through sudoku subgrid to check for specific value
body: <p>Im trying to create a function that given a sudoku board, row, column and value, it iterates through the subgrid to which the row and column belongs to and checks if the value is in that subgrid. I have already made the function that identifies to which subgrid the row and column belongs. Im stuck with the function that checks if the value is in that subgrid.
  Eg:</p>
  <pre><code>check_subgrid(       (3, 9, 1), (2, 3, 5, 8, 6), (6, 1, 4),
                       (8, 7, 6), (1, 2, 7, 8),    (9, 8, 2),
                       (2, 8, 5), (6, 9, 2, 3, 1), (5, 9, 3)
                       ), 0, 1, 9)
  </code></pre>
  <p>This should iterate through: (3,9,1), (8,7,6) and (2,8,5). The output should return True, since 9 in that subgrid, otherwise False.
  So far the code I have is the following:</p>
  <pre><code>def check_subgrid(sudoku, row, column, value)
      x_origin, y_origin = get_subgrid_origin(row, column)
          for x in str(x_origin):
              for y in str(y_origin):
                  for i in range(3):
                   #here I should iterate through every subgrid row looking for the value entered.
  </code></pre>
  <p>I hope I explained my self, if you have any doubt do not hesitate to ask.</p>