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by hermitdev 877 days ago
In practice, this would be solved with `typing.overload`[0].

Using you example:

    from typing import overload
 
    @overload
    def fooify(x: int) -> int:
      ...
 
    @overload
    def fooify(x: list[int]) -> list[int]:
      ...
 
 
    def fooify(x: list[int] | int) -> list[int] | int:
      if isinstance(x, list):
        return [fooify(_x) for _x in x]
      return x * 2
[0] https://docs.python.org/3/library/typing.html#overload
2 comments
nerdponx 877 days ago
And for an example of the practical limits of @overload, take a look at the Pandas type hints: https://github.com/pandas-dev/pandas/blob/dc5586baa9e4731805...

Meanwhile it's not even possible to express such things in other static type systems. So I'm not exactly an unhappy customer, but it does put certain things tantalizingly close, but still out of reach without a ton of clunky boilerplate and LoC explosion.

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gpderetta 876 days ago
> it's not even possible to express such things in other static type systems

what do you mean? It seems relatively straightforward.

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olejorgenb 877 days ago
Or a bound typevar:

    T = TypeVar("T", bound=int | list[int])

    def(x: T) -> T:
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