def enum_words(words_iterable):
    """Return string:
    () -> ''
    ('a') -> 'a'
    ('a', 'b') -> 'a and b'
    ('a', 'b', 'c') -> 'a, b and c'
    """
    ws = words_iterable
    if not ws:
        return ''
    elif len(ws) == 1:
        return ws[0]
    elif len(ws) == 2:
        return f'{ws[0]} and {ws[1]}'
    elif len(ws) >= 3:
        return f"{', '.join(ws[:-1])} and {ws[-1]}"