如何使数据类中的属性只读？

Question

假设我有一个这样的课程：

class C:

    def __init__(self, stuff: int):
        self._stuff = stuff

    @property
    def stuff(self) -> int:
        return self._stuff

然后stuff是只读的：

c = C(stuff=10)
print(c.stuff)  # prints 10

和

c.stuff = 2

按预期失败

属性错误：无法设置属性

如何使用数据类获得相同的行为？如果我也想拥有一个setter，我可以这样做：

@dataclass
class DC:
    stuff: int
    _stuff: int = field(init=False, repr=False)

    @property
    def stuff(self) -> int:
        return self._stuff

    @stuff.setter
    def stuff(self, stuff: int):
        self._stuff = stuff

但是没有这个@stuff.setter部分我怎么能做到呢？

Answer 1

from dataclasses import dataclass

@dataclass(frozen=True)
class YourClass:
    """class definition"""

https://docs.python.org/3/library/dataclasses.html#frozen-instances

类实例化后，当尝试更改其任何属性时，会引发异常。

Answer 2

因为在类定义中使用装饰器本质上会触发@dataclass装饰器使用属性对象作为默认字段，所以效果并不好。您可以在外部设置属性，例如：

>>> from dataclasses import dataclass, field
>>> @dataclass
... class DC:
...     _stuff: int = field(repr=False)
...     stuff: int = field(init=False)
...
>>> DC.stuff = property(lambda self: self._stuff) # dataclass decorator cant see this
>>> dc = DC(42)
>>> dc
DC(stuff=42)
>>> dc.stuff
42
>>> dc.stuff = 99
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute