Python:从类内部访问静态类变量

Question

因此，我尝试创建一个扩展列表的类，并具有将某些特殊属性映射为引用列表的某些部分的额外功能。使用this Py3k doc page ，我创建了以下代码。这个想法是(假设我有一个此类的 sequence 实例)sequence.seq 的行为应该与 sequence[0] 完全相同，并且 sequence.index 的行为应该与 sequence[2] 等完全相同。

它似乎工作得很好，只是我似乎无法访问将属性映射到列表的类变量。

我找到了this SO question ，但要么答案是错误的，要么方法内部有些不同。我还可以使用 self.__class__.__map__ ，但由于我需要 __getattribute__ 内的类变量，这会让我陷入无限递归循环。

>>> class Sequence(list):
...      __map__ = {'seq': 0,
...                 'size': 1,
...                 'index': 2,
...                 'fdbid': 3,
...                 'guide': 4,
...                 'factors': 5,
...                 'clas': 6,
...                 'sorttime': 7,
...                 'time': 8,
...                 'res': 9,
...                 'driver': 10 }
...      
...      def __setattr__(self, name, value): # "Black magic" meta programming to make certain attributes access the list
...           print('Setting atr', name, 'with val', value)
...           try:
...                self[__map__[name]] = value
...           except KeyError:
...                object.__setattr__(self, name, value)
...      
...      def __getattribute__(self, name):
...           print('Getting atr', name)
...           try:
...                return self[__map__[name]]
...           except KeyError:
...                return object.__getattribute__(self, name)
...      
...      def __init__(self, seq=0, size=0, index=0, fdbid=0, guide=None, factors=None, 
...           sorttime=None, time=None):
...                super().__init__([None for i in range(11)]) # Be sure the list has the necessary length
...                self.seq = seq
...                self.index = index
...                self.size = size
...                self.fdbid = fdbid
...                self.guide = ''
...                self.time = time
...                self.sorttime = sorttime
...                self.factors = factors
...                self.res = ''
...                self.driver = ''
... 
>>> a = Sequence()
Setting atr seq with val 0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 31, in __init__
  File "<stdin>", line 17, in __setattr__
NameError: global name '__map__' is not defined

Answer 1

由于在完全定义 Sequence 之前不会调用任何方法，因此您可以毫无问题地引用 Sequence.__map__。例如:

def __setattr(self, name, value):
    print('Setting atr', name, 'with val', value)
    try:
        self[Sequence.__map__[name]] = value
    except KeyError:
        object.__setattr__(self, name, value)

<小时/>

顺便说一句，这里演示了只要同名的实例属性不存在，就可以通过对象访问类属性:

class Foo:
    i = 3
    def __init__(self, overwrite):
        if overwrite:
            self.i = 4

f = Foo(False)
id(f.i) == id(Foo.i)     # Should be True
f = Foo(True)
id(f.i) == id(Foo.i)     # Should be False