Enum

See Literal types in the docs.

Use Literal or Final for a single value.

a: Final = 19
b: Literal[19] = 19

Use the Literal type for possible values.

Colors = Literal["red", "blue", "yellow"]

Example from the docs:

PrimaryColors = Literal["red", "blue", "yellow"]
SecondaryColors = Literal["purple", "green", "orange"]
AllowedColors = Literal[PrimaryColors, SecondaryColors]

def paint(color: AllowedColors) -> None:
    pass

paint("red")        # Valid
paint("turquoise")  # Invalid