def current_red(before, after):
    """
    Checks if the red light works well.
    :param before: has to be None or "yellow"
    :param after: has to be None or "yellow"
    :return: if any constraints not met will return False else True
     """
    print(f'{before}--red--{after}')
    accepted = [None, "yellow"]
    if before not in accepted or after not in accepted:
        return False
    return True