Proposal: LiteralInt

[elenakrittik]

Similar to the LiteralString type, LiteralInt is an integer that is (or is composed of) constant integer literals.

The problem

Identificators (IDs) in many applications are represented as integers, and it is convenient from time to time to just hardcode an entity's ID that you know will not change when the API you use doesn't provide good means to programmatically find the necessary entity. This is the exact use case i have: i want all IDs in a library to be strongly typed and differentiated (so that you can't accidentally misuse, e.g., a user ID when a message ID was expected, as they will be different NewTypes of int), but this creates a limitation: i can no longer pass raw int literal where i used to do so, so i'll need to find all usages of that pattern and update them, which is prohibitive given the amount of code that already depends on this type-checking properly. I can't use something like UserID | int either because that will essentially eliminate the whole point and silently cast NewTypes of other ID types to int and therefore pass the type check. LiteralInt would solve this.

I'd like to hear others' opinion on this: is it worth it? Maybe some other use cases you have? Any feedback appreciated.

[Gobot1234]

I agree it seems like a good idea but I think this'd be much better generalised by Literal[int] working that way you get the other types that work with Literal for free

[elenakrittik]

I was thinking of ArbitraryLiteral, inspired by LiteralString PEP's title ("Arbitrary Literal String Type")

[TeamSpen210]

Perhaps LiteralOf[int]?

[jorenham]

Or perhaps Just[int], for the sake of brevity.

[jorenham]

@Daverball A literal slice-type sounds awesome for integers, but only for integers (and perhaps floats): Literal['spam':] or Literal[Color.RED:] (Color is an enum) don't make much sense.

[jorenham]

Alternatively, what about naming it Constant[int] or Const[int]?

[jorenham]

This would make it possible to provide correct typeshed annotations for len(), which currently upcasts any Literal[:int] returned from __len__() to an int.

[jorenham]

See python/typeshed#11830 for a related discussion

[randolf-scholz]

Another great use case would be for annotating matplotlib's subplot.

Currently, it seems one has to manually add squeeze=False to make the type-checker infer ndarray. With Literal[int] one could write overloads that automatically infer this case if ncols>1 or nrows>1.