Returns a list of flags corresponding to the first time an item is seen

    Args:
        list_ (list): list of items

    Returns:
        flag_iter

def iflag_unique_items(list_):
    """
    Returns a list of flags corresponding to the first time an item is seen

    Args:
        list_ (list): list of items

    Returns:
        flag_iter
    """
    seen = set()
    def unseen(item):
        if item in seen:
            return False
        seen.add(item)
        return True
    flag_iter = (unseen(item) for item in list_)
    return flag_iter