🔒 typing: enforce homogeneous list in function parameter

[pale quarry]

let's say i have a function that takes a homogeneous list and returns one of the items:

def fn[T](xs: list[T]) -> T:
  return xs[0] # just as an example, actual fn is more involved

fn(['a','b','c']) # fine
fn([1,2,3])       # fine
fn([1,2,'c'])     # this should error but doesn't in my editor

1. is it a problem with my pyright setup?
2. is there a different way i should be typing this?

python 3.12.2, pyright

[formal spindle]

@pale quarry

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[jade loom]

in the last case, T just resolves to int | str or object, so there's no problem

[iron bluff]

you cannot force a non-union

[pale quarry]

i don’t want it to resolve to object or a union though, i want it to be a single type across the list or be an error

[iron bluff]

it's simply not possible with passing a literal like this

[pale quarry]

:/

[deep lake]

You can check if T is an Union (I think?) by using typing.get_origin @pale quarry

[iron bluff]

(although that is runtime, right?)

[last basalt]

🤔 Wouldn't that be a runtime check rather than with pyright?

[deep lake]

Oh yeah, I was just thinking in case they didn't find a better solution and wanted to enforce the sameness of T

[pale quarry]

yeah prefer a type check here, thx for the info and suggestions everyone!

disappointing outcome but it is what it is 🙃

[formal spindle]

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