學習Python困難的方式ex43

Question

很抱歉，此問題已被詢問並多次回答。我已經檢查了他們中的大部分，確切的問題並且看到了他們的答案，但是他們要麼對我不起作用，要麼對我的簡單理解來說太沉重。這是我的代碼;

from sys import exit 
from random import randint 

class Scene(object): 

    def enter(self): 
     print("Scene not configured") 
     exit(1) 

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) 

class Death(Scene): 

    quips = [ 
    "Your dead", 
    "rekt", 
    "super rekt"] 

    def enter(self): 
     print(Death.quips[randint(0, len(self.quips)-1)]) 
     exit(1) 

class Corridor(Scene): 

    def enter(self): 
     print("\nYou've a gun and stuff, what will you do? Shoot/Leg it") 

     action = input("\n>> ") 

     if action == "Shoot": 
      print("\nYou killed someone, good stuff") 
      print("You get into the armory.") 
      return 'laser_weapon_armory' 

     elif action == "Leg it": 
      print("\nYou get shot before you get away.") 
      return 'death' 

     else: 
      print("\nThat was not an option") 
      return 'central_corridor' 

class LaserWeaponArmory(Scene): 

    def enter(Self): 
     print("\nRight, you're in the armory.") 
     print("There's a lock on the next door. \nEnter 3 digits to unlock") 
     code = "%d%d%d" % (randint(1,9), randint(1,9), randint(1,9)) 
     guess = input("\n >> ") 
     guesses = 0 

     while guess != code and guesses < 10: 
      print("\nDENIED") 
      guesses += 1 
      guess = input("\n >> ") 

     if guess == code: 
      print("\nDoor opens.") 
      print("You enter the bridge.") 
      return 'the_bridge' 

     else: 
      print("\nDoor remains locked. You get killed") 
      Death() 

class TheBridge(Scene): 

    def enter(Self): 
     print("\nYou're in the bridge.") 
     print("There's a bomb. What do you do?") 
     print("Defuse/Run away") 

     action = input("\n >> ") 

     if action == 'Defuse': 
      print("\nYou failed, bomb goes off") 
      return 'death' 

     elif action == 'Run away': 
      print("\nYou get in the escape pod bay.") 
      return 'escape_pod' 

     else: 
      print("\nThat was not an option.") 
      Death() 

class EscapePod(Scene): 

    def enter(self): 
     print("\nThere's 5 pods, which do you take?") 

     good_pod = randint(1.5) 
     pod = input("\n>>Pod #") 

     if int(pod) != good_pod: 
      print("\nThis pod is fucked.") 
      Death() 

     else: 
      print("\nYurt, the pod works. You're out of here kid.") 
      return 'finished' 

class Finished(Scene): 

    def enter(self): 
     print("\nGame over. Go away.") 
     return 'finished' 

class Map(object): 

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

    def __init__(self, start_scene): 
     self.start_scene = start_scene 
     print("start_scene in __init__", self.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() 

錯誤;

Traceback (most recent call last): 
    File "C:\Python\Shtuff\game.py", line 143, in <module> 
    a_game.play() 
    File "C:\Python\Shtuff\game.py", line 20, in play 
    next_scene_name = current_scene.enter() 
AttributeError: 'NoneType' object has no attribute 'enter' 

我對Python很新，主要是理解類和所有這些。據我所見，這與LPTHW中的代碼完全相同。我已經看到了我在代碼中遇到的確切問題的兩個答案，因此無法看到我要出錯的地方。這可能是我使用Python3和LPTHW所有關於Python 2.XX的事情嗎？

Answer 1

字典的get方法不存在的鍵返回None：

a = {'hello': 'world'} 

print(a.get('hello')) # -> world 
print(a.get('test')) # -> None 

你假設每個場景的enter方法返回下一個場景的名稱。其中一些方法返回'death'（例如，請參閱Corridor和TheBridge）。然後這個返回值被用作Map.scenes的關鍵字。但那裏沒有'death'鍵，所以它返回None。

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順便說一句，self和Self有很大的不同，但您同時使用，並期待他們做同樣的事情。