类变量引用本身？

Question

我是新的编码阶段（3个星期），并一直在建设和重建一个RPG，以帮助教自己的原则，我一直在学习。然而，我似乎停留在Python类的一个特定方面。你知道吗

我为worldLocation类创建的类变量读取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'})

但我希望它改为这样读，每个实例变量引用类变量本身：

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，每次尝试将其更改为后者时，都会收到undefined name WHITEROOM错误。我做错了什么或错过了什么？你知道吗

类别代码如下：

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

您可以完成您想要完成的事情，但是在声明变量之前不能引用它。你知道吗

例如，不能说A={'key':A}，因为在创建dict之前，它不能用作'key'的值。你知道吗

试试这个：

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

为什么这样做？好的，worldLocation构造函数__init__将创建worldLocation对象并将其赋给变量WHITEROOM。然后我们可以使用点操作符访问WHITEROOM.DIRECTIONS变量，并将一个新的dict传递给它，该变量使用WHITEROOM变量作为WHITEROOM对象的引用。 它不像你想的那么优雅，但我想这样你就能做你想做的事了。你知道吗

Answer 2

您要使用的代码试图引用字典中作为参数传递给__init__()的实例，但它不存在。这是不可行的（如果你仔细想想，可以说是非常合理的）。你知道吗

但是，您可以通过创建一个特殊值来解决这个问题，类初始值设定项__init__()方法可以检查并修复正在传递的数据。你知道吗

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，使其能够运行以进行测试。你知道吗

#### 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))

样本输出：

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'}

Answer 3

变量直到函数返回后才获得值，因此不能在函数的参数中引用它。在赋值变量之后，必须添加这些引用。你知道吗

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