ensure literal type from a dynamic value by employing "guard" function in python

python_literal_type_checking.py

"""
seems like hard coding is the only way to make literal type to accept anything to be literal
(which makes sense if you think about it)
"""

from typing import Any, Literal


my_literal_type = Literal["a", "b", "c"]


# I used `Any` type here but you could use `str` if you want to restrict the dynamic value's type to be `str` only
def guard_mlt(value: Any) -> my_literal_type:
    """
    only allow values in my_literal_type to pass
    and otherwise raise TypeError
    this requires hard coding the return values as it's explained at the top

    >>> guard_mlt('a')
    'a'
    >>> guard_mlt('b')
    'b'
    >>> guard_mlt('c')
    'c'
    >>> guard_mlt('d')
    Traceback (most recent call last):
        ...
    TypeError: d is not in typing.Literal['a', 'b', 'c']
    """
    match value:
        case "a":
            return "a"
        case "b":
            return "b"
        case "c":
            return "c"

    raise TypeError(f"{value} is not in {my_literal_type}")


if __name__ == "__main__":
    import doctest

    doctest.testmod()

This is when you need to type check a dynamic value against a literal type similar to the case described at https://stackoverflow.com/questions/72650610/how-can-i-dynamically-test-whether-a-value-conforms-to-a-python-literal-type.