python note

descriptor.py

from dataclasses import Field, dataclass, field, fields

from typing_extensions import dataclass_transform


class FieldDescriptor:
    def __init__(self, field: Field):
        self.field = field

    def __get__(self, instance, owner):
        if instance is None:
            return self.field
        return instance.__dict__.get(self.field.name)

    def __set__(self, instance, value):
        instance.__dict__[self.field.name] = value


@dataclass_transform(field_specifiers=(field, Field))
class Base:
    def __init_subclass__(cls) -> None:
        super().__init_subclass__()
        dataclass(cls)
        _fields = fields(cls)  # type: ignore
        for f in _fields:
            setattr(cls, f.name, FieldDescriptor(f))


class Foo(Base):
    f1: str


if __name__ == "__main__":
    print(type(Foo.f1))  # -> <class 'dataclasses.Field'>
    print(Foo.__dict__)
    obj = Foo(f1="fff")
    print(type(obj.f1))  # -> <class 'str'>
    print(obj.f1)
    print(f"{obj.__class__.__name__}.{obj.__class__}")