docs: def handle_input(self, input_str, place=True, check=False):
          '''Transfer user input to valid chess position'''
          user = self.get_player()
          pos = self.validate_input(input_str)
          if pos[0] == 'u':
              self.undo(pos[1])
              return pos
          if place:
              result = self.set_pos(pos, check)
              return result
          else:
              return pos