[Tutor] Object and Attribute Error

[Alan Thwaits]

Another error message in my game script from Exercise 43 in Zeb Shaw's
"Learn Python the Hard Way."

The first block of code which the error message references is this:

class Engine(object):

    def __init__(self, scene_map):
        self.scene_map = scene_map

    def play(self):
        current_scene = self.scene_map.opening_scene()
        last_scene = self.scene_map.next_scene('finished')

        while current_scene != last_scene:
            next_scene_name = current_scene.enter()
            current_scene = self.scene_map.next_scene(next_scene_name)

        #be sure to print out the last scene
        current_scene.enter()

The second block of code referenced is this:

class Map(object):

    scenes = {
        'central_corridor': CentralCorridor(),
        'laser_weapon_armory': LaserWeaponArmory(),
        'the_bridge': TheBridge(),
        'escape_pod': EscapePod(),
        'death': Death(),
        'finished': Finished(),
    }

    def __init__(self, start_scene):
        self.start_scene = start_scene

    def next_scene(self, scene_name):
        val = Map.scenes.get(scene_name)
        return val

    def opening_scene(self):
        return self.next_scene(self.start_scene)

a_map = Map('central_corridor')
a_game = Engine(a_map)
a_game.play()

The error message is this:

Traceback (most recent call last):

  File "<ipython-input-1-ceaa7049971f>", line 1, in <module>
    runfile('C:/Users/Alan/Documents/Python/ex43.py',
wdir='C:/Users/Alan/Documents/Python')

  File
"C:\Users\Alan\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py",
line 827, in runfile
    execfile(filename, namespace)

  File
"C:\Users\Alan\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py",
line 110, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/Alan/Documents/Python/ex43.py", line 194, in <module>
    a_game.play()

  File "C:/Users/Alan/Documents/Python/ex43.py", line 29, in play
    next_scene_name = current_scene.enter()

AttributeError: 'NoneType' object has no attribute 'enter'

Obviously, I need to understand object and attribute better. Any guidance
would be appreciated.

Thanks!

Alan