python - 如何删除数据类属性

Question

我有一个这样的数据类:

@dataclass
class Bla:
    arg1: Optional[int] = None
    arg2: Optional[str] = None
    arg3: Optional[Dict[str, str]] = None

我想要这种行为:

>>> bla = Bla(arg1=None, arg2=None, arg3=None)
>>> asdict(bla)
{'arg1': None, 'arg2': None, 'arg3': None}

>>> bla = Bla()
{}

在这种特定情况下，我可以使用 dict ，但我会失去类型提示的可能性(并使用 mypy)

所以我试过这个:

class none:
    ...

@dataclass
class Bla:
    arg1: Union[none, int] = none()
    arg2: Union[none, str] = none()
    arg3: Union[none, Dict[str, str]] = none()

    def __post_init__(self) -> None:
        for k, v in self.__dict__.copy().items():
            if isinstance(v, none):
                delattr(self, k)

但结果是:

>>> asdict(Bla())
{'arg1': <__main__.none object at 0x7f71bc0159b0>, 'arg2': <__main__.none object at 0x7f71bc015a90>, 'arg3': <__main__.none object at 0x7f71bc015ac8>}

我期待一个空 dict
如果尝试:

>>> a = Bla(None, None, None)
>>> del a.__dict__["arg1"]
>>> asdict(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/(....)/venv/lib/python3.6/site-packages/dataclasses.py", line 1011, in asdict
    return _asdict_inner(obj, dict_factory)
  File "/home/(...)/venv/lib/python3.6/site-packages/dataclasses.py", line 1018, in _asdict_inner
    value = _asdict_inner(getattr(obj, f.name), dict_factory)
AttributeError: 'Bla' object has no attribute 'arg1'

如何以我可以使用的方式从数据类对象中动态删除属性 asdict在那之后？

Answer 1

这不是您关于从数据类中删除属性的问题的答案，但它提供了一种获取自定义 asdict 的机制。它以您想要的方式运行:

from dataclasses import dataclass
from typing import Optional, Dict, cast

SENTINEL = cast(None, object())  # have a sentinel that pretends to be 'None'


@dataclass
class Bla:
    arg1: Optional[int] = SENTINEL
    arg2: Optional[str] = SENTINEL
    arg3: Optional[Dict[str, str]] = SENTINEL

    def asdict(self):
        return {k: v for k, v in self.__dict__.items() if v is not SENTINEL}

一些测试:

>>> Bla().asdict()
{}
>>> Bla(None, None).asdict()
{'arg1': None, 'arg2': None}
>>> Bla(1, 'foo', None).asdict()
{'arg1': 1, 'arg2': 'foo', 'arg3': None}

但请记住，这都是谎言，当显式调用时，属性仍然存在:

>>> print(Bla().arg1)
<object object at 0x7fc89ed84250>