如何展平NonEmptys的NonEmpty

class NonEmpty:
    def __init__(self, value):
        self.value = value

class NonEmptys:
    def __init__(self, items):
        self.items = items

def flatten(nested):
    result = []
    for item in nested.items:
        if isinstance(item, NonEmptys):
            result.extend(flatten(item))
        elif isinstance(item, NonEmpty):
            result.append(item.value)
    return result

# 示例数据
nested_data = NonEmptys([
    NonEmpty(1),
    NonEmptys([
        NonEmpty(2),
        NonEmpty(3)
    ]),
    NonEmpty(4)
])

# 展平数据
flattened_data = flatten(nested_data)
print(flattened_data)  # 输出: [1, 2, 3, 4]

def flatten(nested, seen=None):
    if seen is None:
        seen = set()
    if id(nested) in seen:
        raise ValueError("Circular reference detected")
    seen.add(id(nested))
    
    result = []
    for item in nested.items:
        if isinstance(item, NonEmptys):
            result.extend(flatten(item, seen))
        elif isinstance(item, NonEmpty):
            result.append(item.value)
    return result