Recipe for a powerful combination of Literals and phantom types ...

phantom-literal.py

from phantom import Phantom
from typing import Literal, get_args, Union, Mapping

from phantom.predicates.collection import contained

LiteralCountry = Literal["SE", "DE", "DK"]


class PhantomCountry(str, Phantom, predicate=contained(get_args(LiteralCountry))):
    ...


Country = Union[LiteralCountry, PhantomCountry]


# -- Usage

# Dynamic values can be parsed, e.g. proven to be a valid value at runtime.
some_var = PhantomCountry.parse("DE")

country_populations: Mapping[Country, int] = {
    some_var: 60,
    # But known valid values don't need to be proven.
    "SE": 9,
    "DK": 4,
}