code: def possible_values(self):
      a = "123456789"
      d, val = {}, {}
      for i in range(self.row):
          for j in range(self.col):
              ele = self.board[i][j]
              if ele != ".":
                  d[("r", i)] = d.get(("r", i), []) + [ele]
                  d[("c", j)] = d.get(("c", j), []) + [ele]
                  d[(i // 3, j // 3)] = d.get((i // 3, j // 3), []) + [
                      ele
                  ]
              else:
                  val[(i, j)] = []
      for i, j in val.keys():
          inval = (
              d.get(("r", i), [])
              + d.get(("c", j), [])
              + d.get((i / 3, j / 3), [])
          )
          val[(i, j)] = [n for n in a if n not in inval]
      return val
  
label_desc: Use image node_id 2 for calling the Sudoku obj's underlying member method code with example usage: obj.possible_values() and returns: val