9.12: Keeping Track of the Location of Things in the Game World

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    grassObjs = []    # stores all the grass objects in the game
    squirrelObjs = [] # stores all the non-player squirrel objects
    # stores the player object:
    playerObj = {'surface': pygame.transform.scale(L_SQUIR_IMG, (STARTSIZE, STARTSIZE)),
                 'facing': LEFT,
                 'size': STARTSIZE,
                 'x': HALF_WINWIDTH,
                 'y': HALF_WINHEIGHT,
                 'bounce':0,
                 'health': MAXHEALTH}

    moveLeft  = False
    moveRight = False
    moveUp    = False
    moveDown  = False

The grassObjs variable holds a list of all the grass objects in the game. As new grass objects are created, they are added to this list. As grass objects are deleted, they are removed from this list. The same goes for the squirrelObjs variable and the enemy squirrel objects.

The playerObj variable is not a list, but just the dictionary value itself.

The move variables on lines 12 [120] to 15 [123] track which of arrow keys (or WASD keys) are being held down, just like in a few of the previous game programs.