code: def flag_field(self, move_x, move_y):
          
          field_status = self.info_map[move_y, move_x]
  
          # a questioned or undiscovered field
          if field_status != 9 and (field_status == 10 or field_status == 11):
              self.info_map[move_y, move_x] = 9
docs: Flag a grid by given position.