def is_magic_choice(attr_name: str) -> bool:
    """Determine iff attr_name meets magic choice formatting requirements.

    This is a helper for MagicKind metaclass that determines if an attribute
    name should be treated as a user defined magic-value choice

    Args:
        attr_name: name of an attribute
    Returns:
        True iff all the following are true about attr_name:
           * Is a valid python identifier.
           * Is upper case.
           * Does not begin with an underscore.
    """
    return (
        attr_name.isupper()
        and attr_name.isidentifier()
        and not attr_name.startswith("_")
    )