python - 如何在不注释类型的情况下添加数据类字段？

Question

当数据类中有一个类型可以是任何类型的字段时，如何省略注释？

@dataclass
class Favs:
    fav_number: int = 80085
    fav_duck = object()
    fav_word: str = 'potato'

似乎上面的代码实际上并没有为fav_duck. 它只是使它成为一个普通的旧类属性。

>>> Favs()
Favs(fav_number=80085, fav_word='potato')
>>> print(*Favs.__dataclass_fields__)
fav_number fav_word
>>> Favs.fav_duck
<object at 0x7fffea519850>

Answer 1

dataclass 装饰器检查类以查找字段，方法是在__annotations__. 正是注释的存在使得该字段，所以，你确实需要一个注释。

但是，您可以使用通用的：

@dataclass
class Favs:
    fav_number: int = 80085
    fav_duck: 'typing.Any' = object()
    fav_word: str = 'potato'

Answer 2

According to PEP 557 which defines the meaning of data classes,

The dataclass decorator examines the class to find fields. A field is defined as any variable identified in __annotations__. That is, a variable that has a type annotation.

Which is to say that the premise of this question (e.g. "How can I use dataclass with a field that has no type annotation) must be rejected. The term 'field' in the context of dataclass necessitates that the attribute has a type annotation by definition.

Note that using a generic type annotation like typing.Any is not the same as having an unannotated attribute, since the attribute will appear in __annotations__.

Finally, the helper function make_dataclass will automatically use typing.Any for the type annotation in cases when only an attribute name is supplied, and this is also mentioned in the PEP with an example.