Python 2.x - 在同一類中創建類的靜態實例

Question

我想在python中編寫一個「枚舉類」。我目前遇到的一個小麻煩是無法在枚舉類中定義枚舉值。也就是說，我可以這樣做：

class Fruit: 
    def __init__(self, name): 
     self.name = name 

class Fruits(Enum): 
    Apple = Fruit("apple") 

但我想這樣做，或者類似的清晰等價的：

class Fruit(Enum): 
    def __init__(self, name): 
     self.name = name 

    Apple = Fruit("apple") 

不幸的是，我收到以下錯誤： 名「果」未定義

這種情況下的可見性規則是什麼？是否有任何鮮爲人知的Python技巧可以幫助我？我更喜歡在Enum的元類中寫入可能的東西，因爲這會使用戶使用起來不那麼麻煩。

Answer 1

你可以做一個元類是做了一些簡單的像這樣：

class MetaEnum(type): 
    def __new__(cls, class_name, parents, attrs): 
     def __init__(self, name=None): 
      if name is not None: self.name = name 
     attrs['__init__'] = __init__ 
     Klass = type.__new__(cls, class_name, parents, attrs) 
     if 'instances' in attrs: 
      for name in attrs['instances']: 
       setattr(Klass, name.capitalize(), Klass(name)) 
      del Klass.instances # clean up 
     return Klass 

class Fruit(object): 
    __metaclass__ = MetaEnum 
    instances = ('apple', 'banana', 'cranberry') 

for attr_name in dir(Fruit): 
    if not attr_name.startswith('_'): 
     attr = getattr(Fruit, attr_name) 
     if type(attr) is Fruit: 
      print('Fruit.{}, is a Fruit named {}'.format(attr_name, getattr(attr, 'name'))) 
     else: 
      print('Fruit.{}, is a {}'.format(attr, type(attr))) 

輸出：

Fruit.Apple, is a Fruit named apple 
Fruit.Banana, is a Fruit named banana 
Fruit.Cranberry, is a Fruit named cranberry