python - 类变量引用本身？

Question

我是编码期的新手(大约 3 周)，并且一直在构建和重建 RPG，以帮助自学我一直在学习的原理。然而，我似乎陷入了 Python 类的一个特定方面。

我为 worldLocation 类创建的类变量读取为 NORTH、EAST、SOUTH >, WEST 所有引用字符串:

WHITEROOM = worldLocation('A Plain White Room',
                          '...\n\nWhere are you?\n\n'
                          'All around you is white...\n\n'
                          '...only white...',
                          [ROCK.GROUNDDESC],
                          [RAT.NAME],
                          {NORTH: 'A Plain White Room',
                           SOUTH: 'A Plain White Room',
                           EAST: 'A Plain White Room',
                           WEST: 'A Plain White Room'})

但我希望它读起来像这样，其中每个实例变量都引用类变量本身:

WHITEROOM = worldLocation('A Plain White Room',
                          '...\n\nWhere are you?\n\n'
                          'All around you is white...\n\n'
                          '...only white...',
                          [ROCK.GROUNDDESC],
                          [RAT.NAME],
                          {NORTH: WHITEROOM,
                           SOUTH: WHITEROOM,
                           EAST: WHITEROOM,
                           WEST: WHITEROOM})

但是，每次我尝试将其更改为后者时，我都会收到 undefined name WHITEROOM 错误。我做错了什么或遗漏了什么？

类代码如下:

class worldLocation(object):
    def __init__(self, NAME, DESC, GROUND, ENEMIES, DIRECTIONS):
        self.NAME = NAME
        self.DESC = DESC
        self.GROUND = GROUND
        self.ENEMIES = ENEMIES
        self.DIRECTIONS = DIRECTIONS

Answer 1

您要使用的代码正在尝试引用字典中的实例，该实例作为参数传递给 __init__() 在存在之前。这是不可行的(如果你仔细想想的话，可以说是非常合理的)。

但是，您可以通过创建一个特殊值来解决该问题，类初始化器 __init__() 方法可以检查并修复正在传递的数据。

下面的代码说明了我的意思。 注意我在开始时添加了一些脚手架，使其可以运行以进行测试。

#### Some scaffolding for testing.
NORTH, SOUTH, EAST, WEST = 'NORTH SOUTH EAST WEST'.split()

class ROCK:
    GROUNDDESC = 'ground desc'

class RAT:
    NAME = 'Ricky'
####


class WorldLocation:
    THIS = object()  # A unique value.

    def __init__(self, NAME, DESC, GROUND, ENEMIES, DIRECTIONS):
        self.NAME = NAME
        self.DESC = DESC
        self.GROUND = GROUND
        self.ENEMIES = ENEMIES

        # Replace any values in DIRECTIONS dictionary argument that refer to the
        # instance being created (as designated by them being the class
        # attribute THIS).
        self.DIRECTIONS = {direction: self if value is self.THIS else value
                               for direction, value in DIRECTIONS.items()}


WHITEROOM = WorldLocation('A Plain White Room',
                          '...\n\nWhere are you?\n\n'
                          'All around you is white...\n\n'
                          '...only white...',
                          [ROCK.GROUNDDESC],
                          [RAT.NAME],
                          {NORTH: WorldLocation.THIS,
                           SOUTH: WorldLocation.THIS,
                           EAST: WorldLocation.THIS,
                           WEST: WorldLocation.THIS})

# Show that it works.
from pprint import pprint

print(f'id(WHITEROOM): 0x{id(WHITEROOM):08x}\n')
pprint(vars(WHITEROOM))

示例输出:

id(WHITEROOM): 0x010d0390

{'DESC': '...\n'
         '\n'
         'Where are you?\n'
         '\n'
         'All around you is white...\n'
         '\n'
         '...only white...',
 'DIRECTIONS': {'EAST': <__main__.WorldLocation object at 0x010D0390>,
                'NORTH': <__main__.WorldLocation object at 0x010D0390>,
                'SOUTH': <__main__.WorldLocation object at 0x010D0390>,
                'WEST': <__main__.WorldLocation object at 0x010D0390>},
 'ENEMIES': ['Ricky'],
 'GROUND': ['ground desc'],
 'NAME': 'A Plain White Room'}