mypy - 短路 `or` 的窄类型，当我有两种可能的情况时

Question

我正在尝试注释以下代码。

当同时定义了 zone 和 zones 时，或者当定义了 file 时(但不是同时定义了两者)，该函数将起作用:

def get_file(zone: str, zones: dict[str, str]) -> pathlib.Path:
    pass

def connect(
        zone: str | None = None,
        zones: dict[str, str] | None = None,
        file: pathlib.Path | None = None,
) -> bool:
    file = file or get_file(zone, zones)

但这让 mypy 生气了 -

1. Argument of type "str | None" cannot be assigned to parameter "zone" of type "str" in function "_get_vpn_file"
     Type "str | None" cannot be assigned to type "str"
       Type "None" cannot be assigned to type "str"
2. Argument of type "dict[str, str] | None" cannot be assigned to parameter "zones" of type "dict[str, str]" in function "_get_vpn_file"
     Type "dict[str, str] | None" cannot be assigned to type "dict[str, str]"
       Type "None" cannot be assigned to type "dict[str, str]"

然后我尝试进行一些激进的类型缩小:

def _check_params_are_ok(
    zone: str | None, zones: dict[str, str] | None, file: pathlib.Path | None,
) -> tuple[str, dict[str, str], None] | tuple[None, None, pathlib.Path]:
    if zone is not None and file is not None:
        raise ValueError("Pass `file` or `zone`, but not both.")

    if zone is not None and zones is None:
        raise ValueError("connect: Must define `zones` when `zone` is defined.")

    if zone is None and file is None:
        raise ValueError("connect: Must define `zone` or `file`.")

    assert file is not None or (zone is not None and zones is not None)

    # Type narrowing
    if zone is not None and zones is not None and file is None:
        return zone, zones, file
    if zone is None and zones is None and file is not None:
        return zone, zones, file

    raise NotImplementedError("This error from _check_params_ok shouldn't happen.")


def connect(
        zone: str | None = None,
        zones: dict[str, str] | None = None,
        file: pathlib.Path | None = None,
) -> bool:
    zone, zones, file = _check_params_are_ok(zone, zones, file)
    file = file or get_file(zone, zones)

而且 mypy 仍然显示相同的错误。

即使添加非常明确的断言，Mypy 仍然显示相同的错误:

    zone, zones, file = _check_params_are_ok(zone, zones, file)
    if file is None:
        assert zone is not None and zones is not None
    file = file or get_file(zone, zones)

目前我找到的最佳解决方案是内联转换类型，但这会影响代码的可读性并使行难以阅读:

    file = file or get_file(cast(str, zone), cast(dict[str, str], zones))

有没有什么好的方法可以缩小类型？

Answer 1

在您的代码中，当您执行 - 正如您所说的那样 - 非常清晰的断言时，您只能在 if< 的主体中分配给 file/声明:

if file is None:
    assert zone is not None and zones is not None
    file = get_file(zone, zones)

# file is now a pathlib.Path object
assert file.is_file()  # this is now valid

那么你会非常明确，mypy 不应该再对此提示了。