类型提示和@singledispatch：如何以可扩展的方式包含 `Union[...]`？

我正在重构一个转换各种日期格式的函数（即 ISO 8601 字符串，datetime.date, datetime.datetime等）转换为 Unix 时间戳。

我想要使​​用新功能@singledispatch而不是类型检查，但我不知道如何保留前一个函数的类型提示：

旧功能：使用类型检查

import datetime
from typing import Union


MyDateTimeType = Union[int, str, datetime.datetime, datetime.date, None]


# How do I retain this functionality with @singledispatch?
#                    ⬇️⬇️⬇️⬇️⬇️⬇️⬇️
def to_unix_ts(date: MyDateTimeType = None) -> Union[int, None]:
    """Convert various date formats to Unix timestamp..."""
    if type(date) is int or date is None:
        return date

    if type(date) is str:
        # Handle string argument...

    elif type(date) is datetime.datetime:
        # Handle datetime argument...

    elif type(date) is datetime.date:
        # Handle date argument...

新功能：使用@singledispatch

import datetime
from functools import singledispatch
from typing import Union


@singledispatch
def to_unix_ts(date) -> Union[int, None]:
    """Handle generic case (probably string type)..."""

@to_unix_ts.register
def _(date: int) -> int:
    return date


@to_unix_ts.register
def _(date: None) -> None:
    return date


@to_unix_ts.register
def _(date: datetime.datetime) -> int:
    return int(date.replace(microsecond=0).timestamp())


# etc...

我已经探索过构建支持的类型，如下所示：

supported_types = [type for type in to_unix_ts.registry.keys()]
MyDateTimeType = Union(supported_types)  # Example, doesn't work

...这样它就可以通过未来的 @singledispatch 注册进行扩展，但我无法让它工作。

我怎样才能添加Union[...]样式类型提示@singledispatch以可扩展的方式运行？

我想这就是你要找的。注意singledispatch需要register(type(None))代替register(None)。不支持register(Union[a, b])，但您可以应用多个register函数的装饰器...

import datetime
from functools import singledispatch
from typing import Union

MyDateTimeType = Union[
    int,
    None,
    datetime.datetime,
    datetime.date
]

@singledispatch
def to_unix_ts(date: MyDateTimeType) -> Union[int, None]:
    raise NotImplementedError

@to_unix_ts.register(int)
@to_unix_ts.register(type(None))
def _(date: Union[int, None]) -> Union[int, None]:
    return date

@to_unix_ts.register(str)
def _(date: str):
    # Handle string argument...

@to_unix_ts.register(datetime.datetime)
def _(date: datetime.datetime):
    # Handle datetime argument...

@to_unix_ts.register(datetime.date)
def _(date: datetime.date):
    # Handle date argument...