Set-based Literal syntax

[jorenham]

allow writing Literal[<args>] as {<args>}, i.e. a set literal, and only a set literal

the same rules apply to <args> as for typing.Literal

this example illustrates that | works in the same way for sets as it does for Literal, making this a rather intuitive syntax, that additionally highlights the unique and unordered nature of Literal types, and automatically disallows unhashable (i.e. immutable) types

type Zero = {False, 0}
type Blank = {"", b""}
type Falsy = Zero | Blank

with the default --target=3.10, this translates to

from typing import Literal, TypeAlias

Zero: TypeAlias = Literal[False, 0]
Blank: TypeAlias = Literal["", b""]
Falsy: TypeAlias = Literal[Zero, Blank]

note that the order isn't lost, as this is but a syntactical conversion

also note that Falsy is a nested Literal, which, unlike union-ed Literals, is automatically unpacked and de-duplicated at runtime, so should for the sake of consistency also be the preferred approach within stubs