Type-hint instances of types passed as TypeVarTuple?

Say I have a function like this that tries to convert a given value to any of a list of given classes:

def convert(obj: Any, *to_classes):
    for class_ in to_classes:
        try:
            return class_(...)
        except:
            pass

Can TypeVarTuple be used to annotate *to_classes along with the corresponding return type? I tried the following:

Ts = TypeVarTuple('Ts')

def convert(obj: Any, *to_classes: Unpack[Ts]) -> Union[Unpack[Ts]]:
    for class_ in to_classes:
        try:
            return class_(...)
        except:
            pass

but that results in hints like Type[A] | Type[B] rather than A | B (for passed types A, B). Is there some way to resolve to instances of the passed types?

I don't think there's a way to do this with TypeVarTuple, but you can use an unpacked tuple instead.

from typing import Any, TypeVar, Unpack
T = TypeVar("T")

def convert(obj: Any, *to_classes: Unpack[tuple[type[T], ...]]) -> T | None:
    for class_ in to_classes:
        try:
            return class_(...)
        except:
            pass

x = convert(1, int, str)
reveal_type(x)  # int | str | None

(Note: This causes the latest version of mypy to crash, but it works fine in pyright.)

Brilliant, works perfectly. Thanks!

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Type-hint instances of types passed as TypeVarTuple? #1347

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Type-hint instances of types passed as TypeVarTuple? #1347

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erictraut commented on Feb 10, 2023

harenbrs commented on Feb 11, 2023

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