new_contents: from copy import deepcopy
  import core
  
  class Session(object):
      def __init__(self, grid):
          self.game = core.Game(grid)
          self.original_game = None
  
      def start(self):
          self.original_game = deepcopy(self.game)
          return self.game.start()
  
      def reset(self):
          if self.original_game:
              self.game = self.original_game
              self.original_game = None
  
subject: Add a Game object wrapper Session