If anyone's still looking for a workaround for this:

typing.Literal[tuple(VALID_ARGUMENTS)]

I'm working with lots of sets of different characters and character sequences and ended up here.

If you're using type aliases defined using the type statement, get_args doesn't work directly. And a Union of Literals is messy, so the below is what I ended up with:

from collections.abc import Sequence, Iterator
from typing import Literal, get_args, TypeAliasType, cast

def get_literal_vals(alias: TypeAliasType) -> frozenset:
    def val(alias: TypeAliasType):
        return alias.__value__
    def args(alias: TypeAliasType):
        return get_args(val(alias))
    def resolveT -> Iterator[T]:
        if isinstance(alias, TypeAliasType):
            for val in resolve(args(alias)):
                yield from resolve(val)
            return
        if isinstance(alias, tuple):
            t_seq = cast(Sequence[T], alias)
            for element in t_seq:
                yield from resolve(element)
            return
        yield alias
    return frozenset(resolve(alias))

type Doubles = Literal["ab", "de", "gh"]
type Triples = Literal["abc", "def", "ghi"]
type DT = Doubles | Triples
dt_set: frozenset[DT] = get_literal_vals(DT)

This has some type checking issues depending on how strict your type checker is but works in practice:

>>> type Triples = Literal["abc", "def", "ghi"]
>>> get_literal_vals(Triples)
frozenset({'def', 'abc', 'ghi'})
>>> type Doubles = Literal["ab", "de", "gh"]
>>> get_literal_vals(Doubles)
frozenset({'gh', 'de', 'ab'})
>>> type DT = Doubles | Triples
>>> get_literal_vals(DT)
frozenset({'ghi', 'de', 'ab', 'abc', 'gh', 'def'})

An interesting side effect of this is that dynamic user input string values can be constrained to a set of specific literal values within conditional branches.

def foo(bar: str):
    if bar in dt_set:
        # bar is considered a literal value in DT
        # by some type checkers.
        pass
    # bar is an unconstrained string value
    # outside of the conditional branch.