import ast


def get_literal_tuple(param_type):
    """
    get literal option from annotation string and return result in tuple.
    """
    s_index: int = str(param_type).index('[')
    e_index: int = str(param_type).index(']')
    str_list = str(param_type)[s_index + 1:e_index]

    res = ast.literal_eval(str_list)
    if res:
        return tuple(res)

    return None