def sevenths(key):
    """Return all the sevenths chords in key in a list."""
    if _sevenths_cache.has_key(key):
        return _sevenths_cache[key]
    res = map(lambda x: seventh(x, key), keys.get_notes(key))
    _sevenths_cache[key] = res
    return res
Return all the sevenths chords in key in a list.