def comma_separated(words):
    """ Takes a list of words and returns a string """
    if len(words) >= 3:
        commas = ", ".join(words[0:-1])
        return f"{commas} and {words[-1]}"
    elif len(words) == 2:
        return f"{words[0]} and {words[1]}"
    else:
        return words[0]