如何更新类实例属性

Question

对于一个汽车品牌'VW'和三个模型，我想创建一个类Car的单个实例，并且仅使用新模型更新其models列表属性：

class Car(object):
    cars = {}

    def __init__(self, brand, model):
        self.brand = brand
        self.models = [model]
        self.cars[brand] = self

    def __new__(self, brand, model):
        if brand in self.cars:
            car = self.cars[brand]
            if not model in car.models:
                car.models.append(model)
                print '....appended model %r to brand %r. result: %r' % (model, brand, car.getModels())
            return car
        else:
            return super(Car, self).__new__(self, brand, model)

    def getModels(self):
        return self.models


cars = []
for i in range(3):
    car = Car(brand='vw', model='model_%s' % i)
    if not car in cars:
        cars.append(car)


for car in cars:
    print car.getModels()

所以，目标是print car.getModels()打印：

['model_0', 'model_1', 'model_2']

相反，我只获得最后一个模型：['model_2']

代码中的错误在哪里？