python - Mypy 提示默认参数值与省略号不兼容

Question

我试图找到一种方法来区分参数是否已传递给方法。例如，我有以下功能:

@dataclass
class Record:
    id: int
    name: str
    completed_at: Optional[date] = None


records = [
    Record(id=1, name="Foo", completed_at=date(2021, 1, 10)),
    Record(id=2, name="Bar", completed_at=date(2021, 1, 11)),
]

def update_record(
    id: int,
    name: Optional[str] = None,
    completed_at: Optional[date] = ...,  # type: ignore
):
    record = next(record for record in records if record.id == id)

    if name is not None:
        record.name = name

    if completed_at is not ...:
        record.completed_at = completed_at

它就像一个魅力，但当我删除 # type: ignore 评论时，mypy 提示以下错误:

error: Incompatible default for argument
"completed_at" (default has type "ellipsis", argument has type
"Optional[date]")  [assignment]
    ... int, name: Optional[str] = None, completed_at: Optional[date] = ...

我已经尝试过使用虚拟“哨兵”对象的解决方案，例如:

DO_NOTHING = object()

def update_record(id, completed_at: Union[DO_NOTHING, None, date] = DO_NOTHING):
    pass

...但在我看来它有点过于冗长。

有没有办法以更简洁的方式做得更好？

Answer 1

似乎 @overload 来自 typing 模块完全符合我的要求。完整示例:

@dataclass
class Record:
    id: int
    name: str
    completed_at: Optional[date] = None


records = [
    Record(id=1, name="Foo", completed_at=date(2021, 1, 10)),
    Record(id=2, name="Bar", completed_at=date(2021, 1, 11)),
]


@overload
def update_record(id: int):
    ...


@overload
def update_record(
    id: int, name: Optional[str] = None, completed_at: Optional[date] = None
):
    ...


def update_record(id: int, *args, **kwargs):
    record = next(record for record in records if record.id == id)

    for field, value in kwargs.items():
        setattr(record, field, value)


def test_update():
    repository = Repository(records)
    repository.update(1, name="Foobar")  # Do nothing with `completed_at` field
    repository.update(2, completed_at=None)  # Set `completed_at` to None
    # repository.update(2, completed_at="2021-01-12")  # Typing error

    assert records == [
        Record(id=1, name="Foobar", completed_at=date(2021, 1, 10)),
        Record(id=2, name="Bar"),
    ]

我希望有人会觉得它有用。