Python 如何在没有dict的情况下创建类对象__

“A”

是元类的实例

“B”

和

“B”

定义了

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu？如何在没有
\uuuuu dict\uuuuuuuuu
的情况下创建类对象？
\uuuuuuuuu slots\uuuuuuuuuuu
不会阻止您为类设置属性，您需要为此重写
\uuuuuuuuuuuu setattr\uuuuuuuuuuuu
。像这样的东西应该可以做到：

class B(type):
    __slots__ = ()

class A(metaclass=B):
    pass

A.test = "test"

演示：

class B(type):
    def __new__(cls, clsname, bases, dct):
        dct['__slots__']  = ('x',)
        return type.__new__(cls, clsname, bases, dct)
    def __setattr__(cls, attr, val):
        if attr not in cls.__slots__:
            raise AttributeError('Can\'t set {!r}'.format(attr))
        else:
            type.__setattr__(cls, attr, val)

class A(metaclass=B):
    pass

>A.x=1
>>>A.y=2
回溯（最近一次呼叫最后一次）：
文件“”，第1行，在
A.y=2
文件“C:\Python27\so.py”，第7行，在\uuu setattr中__
raise AttributeError（'无法设置{！r}'。格式（attr））
AttributeError:无法设置“y”
您不能这样做；类始终具有
\uuu dict\uuu

您只能在类上使用
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
来生成没有
\uuuuuuuuuuuuuuuuuuuu。您通常只会生成几个类，因此在元类上支持
\uuuuu\uuuuu
没有多大意义

不要使用
\uuuuuuuuuuuuuuuuuuuu
来阻止设置属性。使用
\uuuuu setattr\uuuuuu
代替：

>>> A.x = 1
>>> A.y = 2
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    A.y = 2
  File "C:\Python27\so.py", line 7, in __setattr__
    raise AttributeError('Can\'t set {!r}'.format(attr))
AttributeError: Can't set 'y'

为什么您想要一个没有
\uuuuu dict\uuuu
的类？也许有不同的方法来解决这个问题。@NedBatchelder:是的，我想要一个没有dict的类。奇怪的是_slots_在classinstance中工作，而不在metaclassclass中工作。我认为内置类没有dict，但显然它没有显示在dir（）中。例如，hasattr（int，'.'u dict'==True@Damamat：您还没有说明为什么想要一个没有
\uuuu dict\uuuu
的类。口授有什么坏处？你能解释一下吗？纯粹是学术兴趣。所以没有办法定义一个实例已定义了
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
的元类（这样他们的实例就不会有
\uuuuuuuu？这就是我认为OP想要实现的目标。@martineau:我不这么认为；那么为什么要测试
A.test='test'
呢？哎呀，OP问的问题你是对的——我误解了这个问题+1.
class NoAttributesClassMeta(type):
    def __setattr__(cls, name, value):
        if name not in cls.__dict__:
            raise AttributeError("Cannot set attributes")
        type.__setattr__(cls, name, value)