def is_ascii(char: str) ->bool:
    """
    Returns whether or not a single character is an ASCII character.
    :param char: A single character
    :return: If that character is an ASCII character.
    """
    if len(char) == 0:
        raise ValueError('Cannot determine if an empty string is ascii or not.'
            )
    if len(char) > 1:
        raise ValueError('The value {} is not a single character!'.format(char)
            )
    return ord(char) >= 0 and ord(char) <= 127
