如何从嵌套字典中提取字典？

def extract_dict(nested_dict):
    result = {}
    for key, value in nested_dict.items():
        if isinstance(value, dict):
            result[key] = extract_dict(value)
        else:
            result[key] = value
    return result

nested_dict = {
    'key1': 'value1',
    'key2': {
        'nested_key1': 'nested_value1',
        'nested_key2': {
            'nested_nested_key1': 'nested_nested_value1'
        }
    }
}

result_dict = extract_dict(nested_dict)
print(result_dict)

{
    'key1': 'value1',
    'key2.nested_key1': 'nested_value1',
    'key2.nested_key2.nested_nested_key1': 'nested_nested_value1'
}